Imported Upstream version 60upstream/60

80 files changed, 23610 insertions, 0 deletions

diff --git a/src/pkg/go/ast/Makefile b/src/pkg/go/ast/Makefile
new file mode 100644
index 000000000..40be10208
--- /dev/null
+++ b/src/pkg/go/ast/Makefile
@@ -0,0 +1,16 @@
+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../Make.inc
+
+TARG=go/ast
+GOFILES=\
+	ast.go\
+	filter.go\
+	print.go\
+	resolve.go\
+	scope.go\
+	walk.go\
+
+include ../../../Make.pkg
diff --git a/src/pkg/go/ast/ast.go b/src/pkg/go/ast/ast.go
new file mode 100644
index 000000000..22bd5ee22
--- /dev/null
+++ b/src/pkg/go/ast/ast.go
@@ -0,0 +1,914 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package ast declares the types used to represent syntax trees for Go
+// packages.
+//
+package ast
+
+import (
+	"go/token"
+	"unicode"
+	"utf8"
+)
+
+// ----------------------------------------------------------------------------
+// Interfaces
+//
+// There are 3 main classes of nodes: Expressions and type nodes,
+// statement nodes, and declaration nodes. The node names usually
+// match the corresponding Go spec production names to which they
+// correspond. The node fields correspond to the individual parts
+// of the respective productions.
+//
+// All nodes contain position information marking the beginning of
+// the corresponding source text segment; it is accessible via the
+// Pos accessor method. Nodes may contain additional position info
+// for language constructs where comments may be found between parts
+// of the construct (typically any larger, parenthesized subpart).
+// That position information is needed to properly position comments
+// when printing the construct.
+
+// All node types implement the Node interface.
+type Node interface {
+	Pos() token.Pos // position of first character belonging to the node
+	End() token.Pos // position of first character immediately after the node
+}
+
+// All expression nodes implement the Expr interface.
+type Expr interface {
+	Node
+	exprNode()
+}
+
+// All statement nodes implement the Stmt interface.
+type Stmt interface {
+	Node
+	stmtNode()
+}
+
+// All declaration nodes implement the Decl interface.
+type Decl interface {
+	Node
+	declNode()
+}
+
+// ----------------------------------------------------------------------------
+// Comments
+
+// A Comment node represents a single //-style or /*-style comment.
+type Comment struct {
+	Slash token.Pos // position of "/" starting the comment
+	Text  string    // comment text (excluding '\n' for //-style comments)
+}
+
+func (c *Comment) Pos() token.Pos { return c.Slash }
+func (c *Comment) End() token.Pos { return token.Pos(int(c.Slash) + len(c.Text)) }
+
+// A CommentGroup represents a sequence of comments
+// with no other tokens and no empty lines between.
+//
+type CommentGroup struct {
+	List []*Comment // len(List) > 0
+}
+
+func (g *CommentGroup) Pos() token.Pos { return g.List[0].Pos() }
+func (g *CommentGroup) End() token.Pos { return g.List[len(g.List)-1].End() }
+
+// ----------------------------------------------------------------------------
+// Expressions and types
+
+// A Field represents a Field declaration list in a struct type,
+// a method list in an interface type, or a parameter/result declaration
+// in a signature.
+//
+type Field struct {
+	Doc     *CommentGroup // associated documentation; or nil
+	Names   []*Ident      // field/method/parameter names; or nil if anonymous field
+	Type    Expr          // field/method/parameter type
+	Tag     *BasicLit     // field tag; or nil
+	Comment *CommentGroup // line comments; or nil
+}
+
+func (f *Field) Pos() token.Pos {
+	if len(f.Names) > 0 {
+		return f.Names[0].Pos()
+	}
+	return f.Type.Pos()
+}
+
+func (f *Field) End() token.Pos {
+	if f.Tag != nil {
+		return f.Tag.End()
+	}
+	return f.Type.End()
+}
+
+// A FieldList represents a list of Fields, enclosed by parentheses or braces.
+type FieldList struct {
+	Opening token.Pos // position of opening parenthesis/brace, if any
+	List    []*Field  // field list; or nil
+	Closing token.Pos // position of closing parenthesis/brace, if any
+}
+
+func (f *FieldList) Pos() token.Pos {
+	if f.Opening.IsValid() {
+		return f.Opening
+	}
+	// the list should not be empty in this case;
+	// be conservative and guard against bad ASTs
+	if len(f.List) > 0 {
+		return f.List[0].Pos()
+	}
+	return token.NoPos
+}
+
+func (f *FieldList) End() token.Pos {
+	if f.Closing.IsValid() {
+		return f.Closing + 1
+	}
+	// the list should not be empty in this case;
+	// be conservative and guard against bad ASTs
+	if n := len(f.List); n > 0 {
+		return f.List[n-1].End()
+	}
+	return token.NoPos
+}
+
+// NumFields returns the number of (named and anonymous fields) in a FieldList.
+func (f *FieldList) NumFields() int {
+	n := 0
+	if f != nil {
+		for _, g := range f.List {
+			m := len(g.Names)
+			if m == 0 {
+				m = 1 // anonymous field
+			}
+			n += m
+		}
+	}
+	return n
+}
+
+// An expression is represented by a tree consisting of one
+// or more of the following concrete expression nodes.
+//
+type (
+	// A BadExpr node is a placeholder for expressions containing
+	// syntax errors for which no correct expression nodes can be
+	// created.
+	//
+	BadExpr struct {
+		From, To token.Pos // position range of bad expression
+	}
+
+	// An Ident node represents an identifier.
+	Ident struct {
+		NamePos token.Pos // identifier position
+		Name    string    // identifier name
+		Obj     *Object   // denoted object; or nil
+	}
+
+	// An Ellipsis node stands for the "..." type in a
+	// parameter list or the "..." length in an array type.
+	//
+	Ellipsis struct {
+		Ellipsis token.Pos // position of "..."
+		Elt      Expr      // ellipsis element type (parameter lists only); or nil
+	}
+
+	// A BasicLit node represents a literal of basic type.
+	BasicLit struct {
+		ValuePos token.Pos   // literal position
+		Kind     token.Token // token.INT, token.FLOAT, token.IMAG, token.CHAR, or token.STRING
+		Value    string      // literal string; e.g. 42, 0x7f, 3.14, 1e-9, 2.4i, 'a', '\x7f', "foo" or `\m\n\o`
+	}
+
+	// A FuncLit node represents a function literal.
+	FuncLit struct {
+		Type *FuncType  // function type
+		Body *BlockStmt // function body
+	}
+
+	// A CompositeLit node represents a composite literal.
+	CompositeLit struct {
+		Type   Expr      // literal type; or nil
+		Lbrace token.Pos // position of "{"
+		Elts   []Expr    // list of composite elements; or nil
+		Rbrace token.Pos // position of "}"
+	}
+
+	// A ParenExpr node represents a parenthesized expression.
+	ParenExpr struct {
+		Lparen token.Pos // position of "("
+		X      Expr      // parenthesized expression
+		Rparen token.Pos // position of ")"
+	}
+
+	// A SelectorExpr node represents an expression followed by a selector.
+	SelectorExpr struct {
+		X   Expr   // expression
+		Sel *Ident // field selector
+	}
+
+	// An IndexExpr node represents an expression followed by an index.
+	IndexExpr struct {
+		X      Expr      // expression
+		Lbrack token.Pos // position of "["
+		Index  Expr      // index expression
+		Rbrack token.Pos // position of "]"
+	}
+
+	// An SliceExpr node represents an expression followed by slice indices.
+	SliceExpr struct {
+		X      Expr      // expression
+		Lbrack token.Pos // position of "["
+		Low    Expr      // begin of slice range; or nil
+		High   Expr      // end of slice range; or nil
+		Rbrack token.Pos // position of "]"
+	}
+
+	// A TypeAssertExpr node represents an expression followed by a
+	// type assertion.
+	//
+	TypeAssertExpr struct {
+		X    Expr // expression
+		Type Expr // asserted type; nil means type switch X.(type)
+	}
+
+	// A CallExpr node represents an expression followed by an argument list.
+	CallExpr struct {
+		Fun      Expr      // function expression
+		Lparen   token.Pos // position of "("
+		Args     []Expr    // function arguments; or nil
+		Ellipsis token.Pos // position of "...", if any
+		Rparen   token.Pos // position of ")"
+	}
+
+	// A StarExpr node represents an expression of the form "*" Expression.
+	// Semantically it could be a unary "*" expression, or a pointer type.
+	//
+	StarExpr struct {
+		Star token.Pos // position of "*"
+		X    Expr      // operand
+	}
+
+	// A UnaryExpr node represents a unary expression.
+	// Unary "*" expressions are represented via StarExpr nodes.
+	//
+	UnaryExpr struct {
+		OpPos token.Pos   // position of Op
+		Op    token.Token // operator
+		X     Expr        // operand
+	}
+
+	// A BinaryExpr node represents a binary expression.
+	BinaryExpr struct {
+		X     Expr        // left operand
+		OpPos token.Pos   // position of Op
+		Op    token.Token // operator
+		Y     Expr        // right operand
+	}
+
+	// A KeyValueExpr node represents (key : value) pairs
+	// in composite literals.
+	//
+	KeyValueExpr struct {
+		Key   Expr
+		Colon token.Pos // position of ":"
+		Value Expr
+	}
+)
+
+// The direction of a channel type is indicated by one
+// of the following constants.
+//
+type ChanDir int
+
+const (
+	SEND ChanDir = 1 << iota
+	RECV
+)
+
+// A type is represented by a tree consisting of one
+// or more of the following type-specific expression
+// nodes.
+//
+type (
+	// An ArrayType node represents an array or slice type.
+	ArrayType struct {
+		Lbrack token.Pos // position of "["
+		Len    Expr      // Ellipsis node for [...]T array types, nil for slice types
+		Elt    Expr      // element type
+	}
+
+	// A StructType node represents a struct type.
+	StructType struct {
+		Struct     token.Pos  // position of "struct" keyword
+		Fields     *FieldList // list of field declarations
+		Incomplete bool       // true if (source) fields are missing in the Fields list
+	}
+
+	// Pointer types are represented via StarExpr nodes.
+
+	// A FuncType node represents a function type.
+	FuncType struct {
+		Func    token.Pos  // position of "func" keyword
+		Params  *FieldList // (incoming) parameters; or nil
+		Results *FieldList // (outgoing) results; or nil
+	}
+
+	// An InterfaceType node represents an interface type.
+	InterfaceType struct {
+		Interface  token.Pos  // position of "interface" keyword
+		Methods    *FieldList // list of methods
+		Incomplete bool       // true if (source) methods are missing in the Methods list
+	}
+
+	// A MapType node represents a map type.
+	MapType struct {
+		Map   token.Pos // position of "map" keyword
+		Key   Expr
+		Value Expr
+	}
+
+	// A ChanType node represents a channel type.
+	ChanType struct {
+		Begin token.Pos // position of "chan" keyword or "<-" (whichever comes first)
+		Dir   ChanDir   // channel direction
+		Value Expr      // value type
+	}
+)
+
+// Pos and End implementations for expression/type nodes.
+//
+func (x *BadExpr) Pos() token.Pos  { return x.From }
+func (x *Ident) Pos() token.Pos    { return x.NamePos }
+func (x *Ellipsis) Pos() token.Pos { return x.Ellipsis }
+func (x *BasicLit) Pos() token.Pos { return x.ValuePos }
+func (x *FuncLit) Pos() token.Pos  { return x.Type.Pos() }
+func (x *CompositeLit) Pos() token.Pos {
+	if x.Type != nil {
+		return x.Type.Pos()
+	}
+	return x.Lbrace
+}
+func (x *ParenExpr) Pos() token.Pos      { return x.Lparen }
+func (x *SelectorExpr) Pos() token.Pos   { return x.X.Pos() }
+func (x *IndexExpr) Pos() token.Pos      { return x.X.Pos() }
+func (x *SliceExpr) Pos() token.Pos      { return x.X.Pos() }
+func (x *TypeAssertExpr) Pos() token.Pos { return x.X.Pos() }
+func (x *CallExpr) Pos() token.Pos       { return x.Fun.Pos() }
+func (x *StarExpr) Pos() token.Pos       { return x.Star }
+func (x *UnaryExpr) Pos() token.Pos      { return x.OpPos }
+func (x *BinaryExpr) Pos() token.Pos     { return x.X.Pos() }
+func (x *KeyValueExpr) Pos() token.Pos   { return x.Key.Pos() }
+func (x *ArrayType) Pos() token.Pos      { return x.Lbrack }
+func (x *StructType) Pos() token.Pos     { return x.Struct }
+func (x *FuncType) Pos() token.Pos       { return x.Func }
+func (x *InterfaceType) Pos() token.Pos  { return x.Interface }
+func (x *MapType) Pos() token.Pos        { return x.Map }
+func (x *ChanType) Pos() token.Pos       { return x.Begin }
+
+func (x *BadExpr) End() token.Pos { return x.To }
+func (x *Ident) End() token.Pos   { return token.Pos(int(x.NamePos) + len(x.Name)) }
+func (x *Ellipsis) End() token.Pos {
+	if x.Elt != nil {
+		return x.Elt.End()
+	}
+	return x.Ellipsis + 3 // len("...")
+}
+func (x *BasicLit) End() token.Pos     { return token.Pos(int(x.ValuePos) + len(x.Value)) }
+func (x *FuncLit) End() token.Pos      { return x.Body.End() }
+func (x *CompositeLit) End() token.Pos { return x.Rbrace + 1 }
+func (x *ParenExpr) End() token.Pos    { return x.Rparen + 1 }
+func (x *SelectorExpr) End() token.Pos { return x.Sel.End() }
+func (x *IndexExpr) End() token.Pos    { return x.Rbrack + 1 }
+func (x *SliceExpr) End() token.Pos    { return x.Rbrack + 1 }
+func (x *TypeAssertExpr) End() token.Pos {
+	if x.Type != nil {
+		return x.Type.End()
+	}
+	return x.X.End()
+}
+func (x *CallExpr) End() token.Pos     { return x.Rparen + 1 }
+func (x *StarExpr) End() token.Pos     { return x.X.End() }
+func (x *UnaryExpr) End() token.Pos    { return x.X.End() }
+func (x *BinaryExpr) End() token.Pos   { return x.Y.End() }
+func (x *KeyValueExpr) End() token.Pos { return x.Value.End() }
+func (x *ArrayType) End() token.Pos    { return x.Elt.End() }
+func (x *StructType) End() token.Pos   { return x.Fields.End() }
+func (x *FuncType) End() token.Pos {
+	if x.Results != nil {
+		return x.Results.End()
+	}
+	return x.Params.End()
+}
+func (x *InterfaceType) End() token.Pos { return x.Methods.End() }
+func (x *MapType) End() token.Pos       { return x.Value.End() }
+func (x *ChanType) End() token.Pos      { return x.Value.End() }
+
+// exprNode() ensures that only expression/type nodes can be
+// assigned to an ExprNode.
+//
+func (x *BadExpr) exprNode()        {}
+func (x *Ident) exprNode()          {}
+func (x *Ellipsis) exprNode()       {}
+func (x *BasicLit) exprNode()       {}
+func (x *FuncLit) exprNode()        {}
+func (x *CompositeLit) exprNode()   {}
+func (x *ParenExpr) exprNode()      {}
+func (x *SelectorExpr) exprNode()   {}
+func (x *IndexExpr) exprNode()      {}
+func (x *SliceExpr) exprNode()      {}
+func (x *TypeAssertExpr) exprNode() {}
+func (x *CallExpr) exprNode()       {}
+func (x *StarExpr) exprNode()       {}
+func (x *UnaryExpr) exprNode()      {}
+func (x *BinaryExpr) exprNode()     {}
+func (x *KeyValueExpr) exprNode()   {}
+
+func (x *ArrayType) exprNode()     {}
+func (x *StructType) exprNode()    {}
+func (x *FuncType) exprNode()      {}
+func (x *InterfaceType) exprNode() {}
+func (x *MapType) exprNode()       {}
+func (x *ChanType) exprNode()      {}
+
+// ----------------------------------------------------------------------------
+// Convenience functions for Idents
+
+var noPos token.Pos
+
+// NewIdent creates a new Ident without position.
+// Useful for ASTs generated by code other than the Go parser.
+//
+func NewIdent(name string) *Ident { return &Ident{noPos, name, nil} }
+
+// IsExported returns whether name is an exported Go symbol
+// (i.e., whether it begins with an uppercase letter).
+//
+func IsExported(name string) bool {
+	ch, _ := utf8.DecodeRuneInString(name)
+	return unicode.IsUpper(ch)
+}
+
+// IsExported returns whether id is an exported Go symbol
+// (i.e., whether it begins with an uppercase letter).
+//
+func (id *Ident) IsExported() bool { return IsExported(id.Name) }
+
+func (id *Ident) String() string {
+	if id != nil {
+		return id.Name
+	}
+	return "<nil>"
+}
+
+// ----------------------------------------------------------------------------
+// Statements
+
+// A statement is represented by a tree consisting of one
+// or more of the following concrete statement nodes.
+//
+type (
+	// A BadStmt node is a placeholder for statements containing
+	// syntax errors for which no correct statement nodes can be
+	// created.
+	//
+	BadStmt struct {
+		From, To token.Pos // position range of bad statement
+	}
+
+	// A DeclStmt node represents a declaration in a statement list.
+	DeclStmt struct {
+		Decl Decl
+	}
+
+	// An EmptyStmt node represents an empty statement.
+	// The "position" of the empty statement is the position
+	// of the immediately preceding semicolon.
+	//
+	EmptyStmt struct {
+		Semicolon token.Pos // position of preceding ";"
+	}
+
+	// A LabeledStmt node represents a labeled statement.
+	LabeledStmt struct {
+		Label *Ident
+		Colon token.Pos // position of ":"
+		Stmt  Stmt
+	}
+
+	// An ExprStmt node represents a (stand-alone) expression
+	// in a statement list.
+	//
+	ExprStmt struct {
+		X Expr // expression
+	}
+
+	// A SendStmt node represents a send statement.
+	SendStmt struct {
+		Chan  Expr
+		Arrow token.Pos // position of "<-"
+		Value Expr
+	}
+
+	// An IncDecStmt node represents an increment or decrement statement.
+	IncDecStmt struct {
+		X      Expr
+		TokPos token.Pos   // position of Tok
+		Tok    token.Token // INC or DEC
+	}
+
+	// An AssignStmt node represents an assignment or
+	// a short variable declaration.
+	//
+	AssignStmt struct {
+		Lhs    []Expr
+		TokPos token.Pos   // position of Tok
+		Tok    token.Token // assignment token, DEFINE
+		Rhs    []Expr
+	}
+
+	// A GoStmt node represents a go statement.
+	GoStmt struct {
+		Go   token.Pos // position of "go" keyword
+		Call *CallExpr
+	}
+
+	// A DeferStmt node represents a defer statement.
+	DeferStmt struct {
+		Defer token.Pos // position of "defer" keyword
+		Call  *CallExpr
+	}
+
+	// A ReturnStmt node represents a return statement.
+	ReturnStmt struct {
+		Return  token.Pos // position of "return" keyword
+		Results []Expr    // result expressions; or nil
+	}
+
+	// A BranchStmt node represents a break, continue, goto,
+	// or fallthrough statement.
+	//
+	BranchStmt struct {
+		TokPos token.Pos   // position of Tok
+		Tok    token.Token // keyword token (BREAK, CONTINUE, GOTO, FALLTHROUGH)
+		Label  *Ident      // label name; or nil
+	}
+
+	// A BlockStmt node represents a braced statement list.
+	BlockStmt struct {
+		Lbrace token.Pos // position of "{"
+		List   []Stmt
+		Rbrace token.Pos // position of "}"
+	}
+
+	// An IfStmt node represents an if statement.
+	IfStmt struct {
+		If   token.Pos // position of "if" keyword
+		Init Stmt      // initialization statement; or nil
+		Cond Expr      // condition
+		Body *BlockStmt
+		Else Stmt // else branch; or nil
+	}
+
+	// A CaseClause represents a case of an expression or type switch statement.
+	CaseClause struct {
+		Case  token.Pos // position of "case" or "default" keyword
+		List  []Expr    // list of expressions or types; nil means default case
+		Colon token.Pos // position of ":"
+		Body  []Stmt    // statement list; or nil
+	}
+
+	// A SwitchStmt node represents an expression switch statement.
+	SwitchStmt struct {
+		Switch token.Pos  // position of "switch" keyword
+		Init   Stmt       // initialization statement; or nil
+		Tag    Expr       // tag expression; or nil
+		Body   *BlockStmt // CaseClauses only
+	}
+
+	// An TypeSwitchStmt node represents a type switch statement.
+	TypeSwitchStmt struct {
+		Switch token.Pos  // position of "switch" keyword
+		Init   Stmt       // initialization statement; or nil
+		Assign Stmt       // x := y.(type) or y.(type)
+		Body   *BlockStmt // CaseClauses only
+	}
+
+	// A CommClause node represents a case of a select statement.
+	CommClause struct {
+		Case  token.Pos // position of "case" or "default" keyword
+		Comm  Stmt      // send or receive statement; nil means default case
+		Colon token.Pos // position of ":"
+		Body  []Stmt    // statement list; or nil
+	}
+
+	// An SelectStmt node represents a select statement.
+	SelectStmt struct {
+		Select token.Pos  // position of "select" keyword
+		Body   *BlockStmt // CommClauses only
+	}
+
+	// A ForStmt represents a for statement.
+	ForStmt struct {
+		For  token.Pos // position of "for" keyword
+		Init Stmt      // initialization statement; or nil
+		Cond Expr      // condition; or nil
+		Post Stmt      // post iteration statement; or nil
+		Body *BlockStmt
+	}
+
+	// A RangeStmt represents a for statement with a range clause.
+	RangeStmt struct {
+		For        token.Pos   // position of "for" keyword
+		Key, Value Expr        // Value may be nil
+		TokPos     token.Pos   // position of Tok
+		Tok        token.Token // ASSIGN, DEFINE
+		X          Expr        // value to range over
+		Body       *BlockStmt
+	}
+)
+
+// Pos and End implementations for statement nodes.
+//
+func (s *BadStmt) Pos() token.Pos        { return s.From }
+func (s *DeclStmt) Pos() token.Pos       { return s.Decl.Pos() }
+func (s *EmptyStmt) Pos() token.Pos      { return s.Semicolon }
+func (s *LabeledStmt) Pos() token.Pos    { return s.Label.Pos() }
+func (s *ExprStmt) Pos() token.Pos       { return s.X.Pos() }
+func (s *SendStmt) Pos() token.Pos       { return s.Chan.Pos() }
+func (s *IncDecStmt) Pos() token.Pos     { return s.X.Pos() }
+func (s *AssignStmt) Pos() token.Pos     { return s.Lhs[0].Pos() }
+func (s *GoStmt) Pos() token.Pos         { return s.Go }
+func (s *DeferStmt) Pos() token.Pos      { return s.Defer }
+func (s *ReturnStmt) Pos() token.Pos     { return s.Return }
+func (s *BranchStmt) Pos() token.Pos     { return s.TokPos }
+func (s *BlockStmt) Pos() token.Pos      { return s.Lbrace }
+func (s *IfStmt) Pos() token.Pos         { return s.If }
+func (s *CaseClause) Pos() token.Pos     { return s.Case }
+func (s *SwitchStmt) Pos() token.Pos     { return s.Switch }
+func (s *TypeSwitchStmt) Pos() token.Pos { return s.Switch }
+func (s *CommClause) Pos() token.Pos     { return s.Case }
+func (s *SelectStmt) Pos() token.Pos     { return s.Select }
+func (s *ForStmt) Pos() token.Pos        { return s.For }
+func (s *RangeStmt) Pos() token.Pos      { return s.For }
+
+func (s *BadStmt) End() token.Pos  { return s.To }
+func (s *DeclStmt) End() token.Pos { return s.Decl.End() }
+func (s *EmptyStmt) End() token.Pos {
+	return s.Semicolon + 1 /* len(";") */
+}
+func (s *LabeledStmt) End() token.Pos { return s.Stmt.End() }
+func (s *ExprStmt) End() token.Pos    { return s.X.End() }
+func (s *SendStmt) End() token.Pos    { return s.Value.End() }
+func (s *IncDecStmt) End() token.Pos {
+	return s.TokPos + 2 /* len("++") */
+}
+func (s *AssignStmt) End() token.Pos { return s.Rhs[len(s.Rhs)-1].End() }
+func (s *GoStmt) End() token.Pos     { return s.Call.End() }
+func (s *DeferStmt) End() token.Pos  { return s.Call.End() }
+func (s *ReturnStmt) End() token.Pos {
+	if n := len(s.Results); n > 0 {
+		return s.Results[n-1].End()
+	}
+	return s.Return + 6 // len("return")
+}
+func (s *BranchStmt) End() token.Pos {
+	if s.Label != nil {
+		return s.Label.End()
+	}
+	return token.Pos(int(s.TokPos) + len(s.Tok.String()))
+}
+func (s *BlockStmt) End() token.Pos { return s.Rbrace + 1 }
+func (s *IfStmt) End() token.Pos {
+	if s.Else != nil {
+		return s.Else.End()
+	}
+	return s.Body.End()
+}
+func (s *CaseClause) End() token.Pos {
+	if n := len(s.Body); n > 0 {
+		return s.Body[n-1].End()
+	}
+	return s.Colon + 1
+}
+func (s *SwitchStmt) End() token.Pos     { return s.Body.End() }
+func (s *TypeSwitchStmt) End() token.Pos { return s.Body.End() }
+func (s *CommClause) End() token.Pos {
+	if n := len(s.Body); n > 0 {
+		return s.Body[n-1].End()
+	}
+	return s.Colon + 1
+}
+func (s *SelectStmt) End() token.Pos { return s.Body.End() }
+func (s *ForStmt) End() token.Pos    { return s.Body.End() }
+func (s *RangeStmt) End() token.Pos  { return s.Body.End() }
+
+// stmtNode() ensures that only statement nodes can be
+// assigned to a StmtNode.
+//
+func (s *BadStmt) stmtNode()        {}
+func (s *DeclStmt) stmtNode()       {}
+func (s *EmptyStmt) stmtNode()      {}
+func (s *LabeledStmt) stmtNode()    {}
+func (s *ExprStmt) stmtNode()       {}
+func (s *SendStmt) stmtNode()       {}
+func (s *IncDecStmt) stmtNode()     {}
+func (s *AssignStmt) stmtNode()     {}
+func (s *GoStmt) stmtNode()         {}
+func (s *DeferStmt) stmtNode()      {}
+func (s *ReturnStmt) stmtNode()     {}
+func (s *BranchStmt) stmtNode()     {}
+func (s *BlockStmt) stmtNode()      {}
+func (s *IfStmt) stmtNode()         {}
+func (s *CaseClause) stmtNode()     {}
+func (s *SwitchStmt) stmtNode()     {}
+func (s *TypeSwitchStmt) stmtNode() {}
+func (s *CommClause) stmtNode()     {}
+func (s *SelectStmt) stmtNode()     {}
+func (s *ForStmt) stmtNode()        {}
+func (s *RangeStmt) stmtNode()      {}
+
+// ----------------------------------------------------------------------------
+// Declarations
+
+// A Spec node represents a single (non-parenthesized) import,
+// constant, type, or variable declaration.
+//
+type (
+	// The Spec type stands for any of *ImportSpec, *ValueSpec, and *TypeSpec.
+	Spec interface {
+		Node
+		specNode()
+	}
+
+	// An ImportSpec node represents a single package import.
+	ImportSpec struct {
+		Doc     *CommentGroup // associated documentation; or nil
+		Name    *Ident        // local package name (including "."); or nil
+		Path    *BasicLit     // import path
+		Comment *CommentGroup // line comments; or nil
+	}
+
+	// A ValueSpec node represents a constant or variable declaration
+	// (ConstSpec or VarSpec production).
+	//
+	ValueSpec struct {
+		Doc     *CommentGroup // associated documentation; or nil
+		Names   []*Ident      // value names (len(Names) > 0)
+		Type    Expr          // value type; or nil
+		Values  []Expr        // initial values; or nil
+		Comment *CommentGroup // line comments; or nil
+	}
+
+	// A TypeSpec node represents a type declaration (TypeSpec production).
+	TypeSpec struct {
+		Doc     *CommentGroup // associated documentation; or nil
+		Name    *Ident        // type name
+		Type    Expr          // *Ident, *ParenExpr, *SelectorExpr, *StarExpr, or any of the *XxxTypes
+		Comment *CommentGroup // line comments; or nil
+	}
+)
+
+// Pos and End implementations for spec nodes.
+//
+func (s *ImportSpec) Pos() token.Pos {
+	if s.Name != nil {
+		return s.Name.Pos()
+	}
+	return s.Path.Pos()
+}
+func (s *ValueSpec) Pos() token.Pos { return s.Names[0].Pos() }
+func (s *TypeSpec) Pos() token.Pos  { return s.Name.Pos() }
+
+func (s *ImportSpec) End() token.Pos { return s.Path.End() }
+func (s *ValueSpec) End() token.Pos {
+	if n := len(s.Values); n > 0 {
+		return s.Values[n-1].End()
+	}
+	if s.Type != nil {
+		return s.Type.End()
+	}
+	return s.Names[len(s.Names)-1].End()
+}
+func (s *TypeSpec) End() token.Pos { return s.Type.End() }
+
+// specNode() ensures that only spec nodes can be
+// assigned to a Spec.
+//
+func (s *ImportSpec) specNode() {}
+func (s *ValueSpec) specNode()  {}
+func (s *TypeSpec) specNode()   {}
+
+// A declaration is represented by one of the following declaration nodes.
+//
+type (
+	// A BadDecl node is a placeholder for declarations containing
+	// syntax errors for which no correct declaration nodes can be
+	// created.
+	//
+	BadDecl struct {
+		From, To token.Pos // position range of bad declaration
+	}
+
+	// A GenDecl node (generic declaration node) represents an import,
+	// constant, type or variable declaration. A valid Lparen position
+	// (Lparen.Line > 0) indicates a parenthesized declaration.
+	//
+	// Relationship between Tok value and Specs element type:
+	//
+	//	token.IMPORT  *ImportSpec
+	//	token.CONST   *ValueSpec
+	//	token.TYPE    *TypeSpec
+	//	token.VAR     *ValueSpec
+	//
+	GenDecl struct {
+		Doc    *CommentGroup // associated documentation; or nil
+		TokPos token.Pos     // position of Tok
+		Tok    token.Token   // IMPORT, CONST, TYPE, VAR
+		Lparen token.Pos     // position of '(', if any
+		Specs  []Spec
+		Rparen token.Pos // position of ')', if any
+	}
+
+	// A FuncDecl node represents a function declaration.
+	FuncDecl struct {
+		Doc  *CommentGroup // associated documentation; or nil
+		Recv *FieldList    // receiver (methods); or nil (functions)
+		Name *Ident        // function/method name
+		Type *FuncType     // position of Func keyword, parameters and results
+		Body *BlockStmt    // function body; or nil (forward declaration)
+	}
+)
+
+// Pos and End implementations for declaration nodes.
+//
+func (d *BadDecl) Pos() token.Pos  { return d.From }
+func (d *GenDecl) Pos() token.Pos  { return d.TokPos }
+func (d *FuncDecl) Pos() token.Pos { return d.Type.Pos() }
+
+func (d *BadDecl) End() token.Pos { return d.To }
+func (d *GenDecl) End() token.Pos {
+	if d.Rparen.IsValid() {
+		return d.Rparen + 1
+	}
+	return d.Specs[0].End()
+}
+func (d *FuncDecl) End() token.Pos {
+	if d.Body != nil {
+		return d.Body.End()
+	}
+	return d.Type.End()
+}
+
+// declNode() ensures that only declaration nodes can be
+// assigned to a DeclNode.
+//
+func (d *BadDecl) declNode()  {}
+func (d *GenDecl) declNode()  {}
+func (d *FuncDecl) declNode() {}
+
+// ----------------------------------------------------------------------------
+// Files and packages
+
+// A File node represents a Go source file.
+//
+// The Comments list contains all comments in the source file in order of
+// appearance, including the comments that are pointed to from other nodes
+// via Doc and Comment fields.
+//
+type File struct {
+	Doc        *CommentGroup   // associated documentation; or nil
+	Package    token.Pos       // position of "package" keyword
+	Name       *Ident          // package name
+	Decls      []Decl          // top-level declarations; or nil
+	Scope      *Scope          // package scope (this file only)
+	Imports    []*ImportSpec   // imports in this file
+	Unresolved []*Ident        // unresolved identifiers in this file
+	Comments   []*CommentGroup // list of all comments in the source file
+}
+
+func (f *File) Pos() token.Pos { return f.Package }
+func (f *File) End() token.Pos {
+	if n := len(f.Decls); n > 0 {
+		return f.Decls[n-1].End()
+	}
+	return f.Name.End()
+}
+
+// A Package node represents a set of source files
+// collectively building a Go package.
+//
+type Package struct {
+	Name    string             // package name
+	Scope   *Scope             // package scope across all files
+	Imports map[string]*Object // map of package id -> package object
+	Files   map[string]*File   // Go source files by filename
+}
+
+func (p *Package) Pos() token.Pos { return token.NoPos }
+func (p *Package) End() token.Pos { return token.NoPos }
diff --git a/src/pkg/go/ast/filter.go b/src/pkg/go/ast/filter.go
new file mode 100644
index 000000000..26733430d
--- /dev/null
+++ b/src/pkg/go/ast/filter.go
@@ -0,0 +1,475 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ast
+
+import "go/token"
+
+// ----------------------------------------------------------------------------
+// Export filtering
+
+func identListExports(list []*Ident) []*Ident {
+	j := 0
+	for _, x := range list {
+		if x.IsExported() {
+			list[j] = x
+			j++
+		}
+	}
+	return list[0:j]
+}
+
+// fieldName assumes that x is the type of an anonymous field and
+// returns the corresponding field name. If x is not an acceptable
+// anonymous field, the result is nil.
+//
+func fieldName(x Expr) *Ident {
+	switch t := x.(type) {
+	case *Ident:
+		return t
+	case *SelectorExpr:
+		if _, ok := t.X.(*Ident); ok {
+			return t.Sel
+		}
+	case *StarExpr:
+		return fieldName(t.X)
+	}
+	return nil
+}
+
+func fieldListExports(fields *FieldList) (removedFields bool) {
+	if fields == nil {
+		return
+	}
+	list := fields.List
+	j := 0
+	for _, f := range list {
+		exported := false
+		if len(f.Names) == 0 {
+			// anonymous field
+			// (Note that a non-exported anonymous field
+			// may still refer to a type with exported
+			// fields, so this is not absolutely correct.
+			// However, this cannot be done w/o complete
+			// type information.)
+			name := fieldName(f.Type)
+			exported = name != nil && name.IsExported()
+		} else {
+			n := len(f.Names)
+			f.Names = identListExports(f.Names)
+			if len(f.Names) < n {
+				removedFields = true
+			}
+			exported = len(f.Names) > 0
+		}
+		if exported {
+			typeExports(f.Type)
+			list[j] = f
+			j++
+		}
+	}
+	if j < len(list) {
+		removedFields = true
+	}
+	fields.List = list[0:j]
+	return
+}
+
+func paramListExports(fields *FieldList) {
+	if fields == nil {
+		return
+	}
+	for _, f := range fields.List {
+		typeExports(f.Type)
+	}
+}
+
+func typeExports(typ Expr) {
+	switch t := typ.(type) {
+	case *ArrayType:
+		typeExports(t.Elt)
+	case *StructType:
+		if fieldListExports(t.Fields) {
+			t.Incomplete = true
+		}
+	case *FuncType:
+		paramListExports(t.Params)
+		paramListExports(t.Results)
+	case *InterfaceType:
+		if fieldListExports(t.Methods) {
+			t.Incomplete = true
+		}
+	case *MapType:
+		typeExports(t.Key)
+		typeExports(t.Value)
+	case *ChanType:
+		typeExports(t.Value)
+	}
+}
+
+func specExports(spec Spec) bool {
+	switch s := spec.(type) {
+	case *ValueSpec:
+		s.Names = identListExports(s.Names)
+		if len(s.Names) > 0 {
+			typeExports(s.Type)
+			return true
+		}
+	case *TypeSpec:
+		if s.Name.IsExported() {
+			typeExports(s.Type)
+			return true
+		}
+	}
+	return false
+}
+
+func specListExports(list []Spec) []Spec {
+	j := 0
+	for _, s := range list {
+		if specExports(s) {
+			list[j] = s
+			j++
+		}
+	}
+	return list[0:j]
+}
+
+func declExports(decl Decl) bool {
+	switch d := decl.(type) {
+	case *GenDecl:
+		d.Specs = specListExports(d.Specs)
+		return len(d.Specs) > 0
+	case *FuncDecl:
+		d.Body = nil // strip body
+		return d.Name.IsExported()
+	}
+	return false
+}
+
+// FileExports trims the AST for a Go source file in place such that only
+// exported nodes remain: all top-level identifiers which are not exported
+// and their associated information (such as type, initial value, or function
+// body) are removed. Non-exported fields and methods of exported types are
+// stripped, and the function bodies of exported functions are set to nil.
+// The File.comments list is not changed.
+//
+// FileExports returns true if there is an exported declaration; it returns
+// false otherwise.
+//
+func FileExports(src *File) bool {
+	j := 0
+	for _, d := range src.Decls {
+		if declExports(d) {
+			src.Decls[j] = d
+			j++
+		}
+	}
+	src.Decls = src.Decls[0:j]
+	return j > 0
+}
+
+// PackageExports trims the AST for a Go package in place such that only
+// exported nodes remain. The pkg.Files list is not changed, so that file
+// names and top-level package comments don't get lost.
+//
+// PackageExports returns true if there is an exported declaration; it
+// returns false otherwise.
+//
+func PackageExports(pkg *Package) bool {
+	hasExports := false
+	for _, f := range pkg.Files {
+		if FileExports(f) {
+			hasExports = true
+		}
+	}
+	return hasExports
+}
+
+// ----------------------------------------------------------------------------
+// General filtering
+
+type Filter func(string) bool
+
+func filterIdentList(list []*Ident, f Filter) []*Ident {
+	j := 0
+	for _, x := range list {
+		if f(x.Name) {
+			list[j] = x
+			j++
+		}
+	}
+	return list[0:j]
+}
+
+func filterFieldList(fields *FieldList, filter Filter) (removedFields bool) {
+	if fields == nil {
+		return false
+	}
+	list := fields.List
+	j := 0
+	for _, f := range list {
+		keepField := false
+		if len(f.Names) == 0 {
+			// anonymous field
+			name := fieldName(f.Type)
+			keepField = name != nil && filter(name.Name)
+		} else {
+			n := len(f.Names)
+			f.Names = filterIdentList(f.Names, filter)
+			if len(f.Names) < n {
+				removedFields = true
+			}
+			keepField = len(f.Names) > 0
+		}
+		if keepField {
+			list[j] = f
+			j++
+		}
+	}
+	if j < len(list) {
+		removedFields = true
+	}
+	fields.List = list[0:j]
+	return
+}
+
+func filterSpec(spec Spec, f Filter) bool {
+	switch s := spec.(type) {
+	case *ValueSpec:
+		s.Names = filterIdentList(s.Names, f)
+		return len(s.Names) > 0
+	case *TypeSpec:
+		if f(s.Name.Name) {
+			return true
+		}
+		switch t := s.Type.(type) {
+		case *StructType:
+			if filterFieldList(t.Fields, f) {
+				t.Incomplete = true
+			}
+			return len(t.Fields.List) > 0
+		case *InterfaceType:
+			if filterFieldList(t.Methods, f) {
+				t.Incomplete = true
+			}
+			return len(t.Methods.List) > 0
+		}
+	}
+	return false
+}
+
+func filterSpecList(list []Spec, f Filter) []Spec {
+	j := 0
+	for _, s := range list {
+		if filterSpec(s, f) {
+			list[j] = s
+			j++
+		}
+	}
+	return list[0:j]
+}
+
+// FilterDecl trims the AST for a Go declaration in place by removing
+// all names (including struct field and interface method names, but
+// not from parameter lists) that don't pass through the filter f.
+//
+// FilterDecl returns true if there are any declared names left after
+// filtering; it returns false otherwise.
+//
+func FilterDecl(decl Decl, f Filter) bool {
+	switch d := decl.(type) {
+	case *GenDecl:
+		d.Specs = filterSpecList(d.Specs, f)
+		return len(d.Specs) > 0
+	case *FuncDecl:
+		return f(d.Name.Name)
+	}
+	return false
+}
+
+// FilterFile trims the AST for a Go file in place by removing all
+// names from top-level declarations (including struct field and
+// interface method names, but not from parameter lists) that don't
+// pass through the filter f. If the declaration is empty afterwards,
+// the declaration is removed from the AST.
+// The File.comments list is not changed.
+//
+// FilterFile returns true if there are any top-level declarations
+// left after filtering; it returns false otherwise.
+//
+func FilterFile(src *File, f Filter) bool {
+	j := 0
+	for _, d := range src.Decls {
+		if FilterDecl(d, f) {
+			src.Decls[j] = d
+			j++
+		}
+	}
+	src.Decls = src.Decls[0:j]
+	return j > 0
+}
+
+// FilterPackage trims the AST for a Go package in place by removing all
+// names from top-level declarations (including struct field and
+// interface method names, but not from parameter lists) that don't
+// pass through the filter f. If the declaration is empty afterwards,
+// the declaration is removed from the AST.
+// The pkg.Files list is not changed, so that file names and top-level
+// package comments don't get lost.
+//
+// FilterPackage returns true if there are any top-level declarations
+// left after filtering; it returns false otherwise.
+//
+func FilterPackage(pkg *Package, f Filter) bool {
+	hasDecls := false
+	for _, src := range pkg.Files {
+		if FilterFile(src, f) {
+			hasDecls = true
+		}
+	}
+	return hasDecls
+}
+
+// ----------------------------------------------------------------------------
+// Merging of package files
+
+// The MergeMode flags control the behavior of MergePackageFiles.
+type MergeMode uint
+
+const (
+	// If set, duplicate function declarations are excluded.
+	FilterFuncDuplicates MergeMode = 1 << iota
+	// If set, comments that are not associated with a specific
+	// AST node (as Doc or Comment) are excluded.
+	FilterUnassociatedComments
+)
+
+// separator is an empty //-style comment that is interspersed between
+// different comment groups when they are concatenated into a single group
+//
+var separator = &Comment{noPos, "//"}
+
+// MergePackageFiles creates a file AST by merging the ASTs of the
+// files belonging to a package. The mode flags control merging behavior.
+//
+func MergePackageFiles(pkg *Package, mode MergeMode) *File {
+	// Count the number of package docs, comments and declarations across
+	// all package files.
+	ndocs := 0
+	ncomments := 0
+	ndecls := 0
+	for _, f := range pkg.Files {
+		if f.Doc != nil {
+			ndocs += len(f.Doc.List) + 1 // +1 for separator
+		}
+		ncomments += len(f.Comments)
+		ndecls += len(f.Decls)
+	}
+
+	// Collect package comments from all package files into a single
+	// CommentGroup - the collected package documentation. The order
+	// is unspecified. In general there should be only one file with
+	// a package comment; but it's better to collect extra comments
+	// than drop them on the floor.
+	var doc *CommentGroup
+	var pos token.Pos
+	if ndocs > 0 {
+		list := make([]*Comment, ndocs-1) // -1: no separator before first group
+		i := 0
+		for _, f := range pkg.Files {
+			if f.Doc != nil {
+				if i > 0 {
+					// not the first group - add separator
+					list[i] = separator
+					i++
+				}
+				for _, c := range f.Doc.List {
+					list[i] = c
+					i++
+				}
+				if f.Package > pos {
+					// Keep the maximum package clause position as
+					// position for the package clause of the merged
+					// files.
+					pos = f.Package
+				}
+			}
+		}
+		doc = &CommentGroup{list}
+	}
+
+	// Collect declarations from all package files.
+	var decls []Decl
+	if ndecls > 0 {
+		decls = make([]Decl, ndecls)
+		funcs := make(map[string]int) // map of global function name -> decls index
+		i := 0                        // current index
+		n := 0                        // number of filtered entries
+		for _, f := range pkg.Files {
+			for _, d := range f.Decls {
+				if mode&FilterFuncDuplicates != 0 {
+					// A language entity may be declared multiple
+					// times in different package files; only at
+					// build time declarations must be unique.
+					// For now, exclude multiple declarations of
+					// functions - keep the one with documentation.
+					//
+					// TODO(gri): Expand this filtering to other
+					//            entities (const, type, vars) if
+					//            multiple declarations are common.
+					if f, isFun := d.(*FuncDecl); isFun {
+						name := f.Name.Name
+						if j, exists := funcs[name]; exists {
+							// function declared already
+							if decls[j] != nil && decls[j].(*FuncDecl).Doc == nil {
+								// existing declaration has no documentation;
+								// ignore the existing declaration
+								decls[j] = nil
+							} else {
+								// ignore the new declaration
+								d = nil
+							}
+							n++ // filtered an entry
+						} else {
+							funcs[name] = i
+						}
+					}
+				}
+				decls[i] = d
+				i++
+			}
+		}
+
+		// Eliminate nil entries from the decls list if entries were
+		// filtered. We do this using a 2nd pass in order to not disturb
+		// the original declaration order in the source (otherwise, this
+		// would also invalidate the monotonically increasing position
+		// info within a single file).
+		if n > 0 {
+			i = 0
+			for _, d := range decls {
+				if d != nil {
+					decls[i] = d
+					i++
+				}
+			}
+			decls = decls[0:i]
+		}
+	}
+
+	// Collect comments from all package files.
+	var comments []*CommentGroup
+	if mode&FilterUnassociatedComments == 0 {
+		comments = make([]*CommentGroup, ncomments)
+		i := 0
+		for _, f := range pkg.Files {
+			i += copy(comments[i:], f.Comments)
+		}
+	}
+
+	// TODO(gri) need to compute pkgScope and unresolved identifiers!
+	// TODO(gri) need to compute imports!
+	return &File{doc, pos, NewIdent(pkg.Name), decls, nil, nil, nil, comments}
+}
diff --git a/src/pkg/go/ast/print.go b/src/pkg/go/ast/print.go
new file mode 100644
index 000000000..62a30481d
--- /dev/null
+++ b/src/pkg/go/ast/print.go
@@ -0,0 +1,224 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file contains printing suppport for ASTs.
+
+package ast
+
+import (
+	"fmt"
+	"go/token"
+	"io"
+	"os"
+	"reflect"
+)
+
+// A FieldFilter may be provided to Fprint to control the output.
+type FieldFilter func(name string, value reflect.Value) bool
+
+// NotNilFilter returns true for field values that are not nil;
+// it returns false otherwise.
+func NotNilFilter(_ string, v reflect.Value) bool {
+	switch v.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Ptr, reflect.Slice:
+		return !v.IsNil()
+	}
+	return true
+}
+
+// Fprint prints the (sub-)tree starting at AST node x to w.
+// If fset != nil, position information is interpreted relative
+// to that file set. Otherwise positions are printed as integer
+// values (file set specific offsets).
+//
+// A non-nil FieldFilter f may be provided to control the output:
+// struct fields for which f(fieldname, fieldvalue) is true are
+// are printed; all others are filtered from the output.
+//
+func Fprint(w io.Writer, fset *token.FileSet, x interface{}, f FieldFilter) (n int, err os.Error) {
+	// setup printer
+	p := printer{
+		output: w,
+		fset:   fset,
+		filter: f,
+		ptrmap: make(map[interface{}]int),
+		last:   '\n', // force printing of line number on first line
+	}
+
+	// install error handler
+	defer func() {
+		n = p.written
+		if e := recover(); e != nil {
+			err = e.(localError).err // re-panics if it's not a localError
+		}
+	}()
+
+	// print x
+	if x == nil {
+		p.printf("nil\n")
+		return
+	}
+	p.print(reflect.ValueOf(x))
+	p.printf("\n")
+
+	return
+}
+
+// Print prints x to standard output, skipping nil fields.
+// Print(fset, x) is the same as Fprint(os.Stdout, fset, x, NotNilFilter).
+func Print(fset *token.FileSet, x interface{}) (int, os.Error) {
+	return Fprint(os.Stdout, fset, x, NotNilFilter)
+}
+
+type printer struct {
+	output  io.Writer
+	fset    *token.FileSet
+	filter  FieldFilter
+	ptrmap  map[interface{}]int // *T -> line number
+	written int                 // number of bytes written to output
+	indent  int                 // current indentation level
+	last    byte                // the last byte processed by Write
+	line    int                 // current line number
+}
+
+var indent = []byte(".  ")
+
+func (p *printer) Write(data []byte) (n int, err os.Error) {
+	var m int
+	for i, b := range data {
+		// invariant: data[0:n] has been written
+		if b == '\n' {
+			m, err = p.output.Write(data[n : i+1])
+			n += m
+			if err != nil {
+				return
+			}
+			p.line++
+		} else if p.last == '\n' {
+			_, err = fmt.Fprintf(p.output, "%6d  ", p.line)
+			if err != nil {
+				return
+			}
+			for j := p.indent; j > 0; j-- {
+				_, err = p.output.Write(indent)
+				if err != nil {
+					return
+				}
+			}
+		}
+		p.last = b
+	}
+	m, err = p.output.Write(data[n:])
+	n += m
+	return
+}
+
+// localError wraps locally caught os.Errors so we can distinguish
+// them from genuine panics which we don't want to return as errors.
+type localError struct {
+	err os.Error
+}
+
+// printf is a convenience wrapper that takes care of print errors.
+func (p *printer) printf(format string, args ...interface{}) {
+	n, err := fmt.Fprintf(p, format, args...)
+	p.written += n
+	if err != nil {
+		panic(localError{err})
+	}
+}
+
+// Implementation note: Print is written for AST nodes but could be
+// used to print arbitrary data structures; such a version should
+// probably be in a different package.
+//
+// Note: This code detects (some) cycles created via pointers but
+// not cycles that are created via slices or maps containing the
+// same slice or map. Code for general data structures probably
+// should catch those as well.
+
+func (p *printer) print(x reflect.Value) {
+	if !NotNilFilter("", x) {
+		p.printf("nil")
+		return
+	}
+
+	switch x.Kind() {
+	case reflect.Interface:
+		p.print(x.Elem())
+
+	case reflect.Map:
+		p.printf("%s (len = %d) {\n", x.Type().String(), x.Len())
+		p.indent++
+		for _, key := range x.MapKeys() {
+			p.print(key)
+			p.printf(": ")
+			p.print(x.MapIndex(key))
+			p.printf("\n")
+		}
+		p.indent--
+		p.printf("}")
+
+	case reflect.Ptr:
+		p.printf("*")
+		// type-checked ASTs may contain cycles - use ptrmap
+		// to keep track of objects that have been printed
+		// already and print the respective line number instead
+		ptr := x.Interface()
+		if line, exists := p.ptrmap[ptr]; exists {
+			p.printf("(obj @ %d)", line)
+		} else {
+			p.ptrmap[ptr] = p.line
+			p.print(x.Elem())
+		}
+
+	case reflect.Slice:
+		if s, ok := x.Interface().([]byte); ok {
+			p.printf("%#q", s)
+			return
+		}
+		p.printf("%s (len = %d) {\n", x.Type().String(), x.Len())
+		p.indent++
+		for i, n := 0, x.Len(); i < n; i++ {
+			p.printf("%d: ", i)
+			p.print(x.Index(i))
+			p.printf("\n")
+		}
+		p.indent--
+		p.printf("}")
+
+	case reflect.Struct:
+		p.printf("%s {\n", x.Type().String())
+		p.indent++
+		t := x.Type()
+		for i, n := 0, t.NumField(); i < n; i++ {
+			name := t.Field(i).Name
+			value := x.Field(i)
+			if p.filter == nil || p.filter(name, value) {
+				p.printf("%s: ", name)
+				p.print(value)
+				p.printf("\n")
+			}
+		}
+		p.indent--
+		p.printf("}")
+
+	default:
+		v := x.Interface()
+		switch v := v.(type) {
+		case string:
+			// print strings in quotes
+			p.printf("%q", v)
+			return
+		case token.Pos:
+			// position values can be printed nicely if we have a file set
+			if p.fset != nil {
+				p.printf("%s", p.fset.Position(v))
+				return
+			}
+		}
+		// default
+		p.printf("%v", v)
+	}
+}
diff --git a/src/pkg/go/ast/print_test.go b/src/pkg/go/ast/print_test.go
new file mode 100644
index 000000000..f4e8f7a78
--- /dev/null
+++ b/src/pkg/go/ast/print_test.go
@@ -0,0 +1,77 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ast
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+var tests = []struct {
+	x interface{} // x is printed as s
+	s string
+}{
+	// basic types
+	{nil, "0  nil"},
+	{true, "0  true"},
+	{42, "0  42"},
+	{3.14, "0  3.14"},
+	{1 + 2.718i, "0  (1+2.718i)"},
+	{"foobar", "0  \"foobar\""},
+
+	// maps
+	{map[string]int{"a": 1, "b": 2},
+		`0  map[string] int (len = 2) {
+		1  .  "a": 1
+		2  .  "b": 2
+		3  }`},
+
+	// pointers
+	{new(int), "0  *0"},
+
+	// slices
+	{[]int{1, 2, 3},
+		`0  []int (len = 3) {
+		1  .  0: 1
+		2  .  1: 2
+		3  .  2: 3
+		4  }`},
+
+	// structs
+	{struct{ x, y int }{42, 991},
+		`0  struct { x int; y int } {
+		1  .  x: 42
+		2  .  y: 991
+		3  }`},
+}
+
+// Split s into lines, trim whitespace from all lines, and return
+// the concatenated non-empty lines.
+func trim(s string) string {
+	lines := strings.Split(s, "\n")
+	i := 0
+	for _, line := range lines {
+		line = strings.TrimSpace(line)
+		if line != "" {
+			lines[i] = line
+			i++
+		}
+	}
+	return strings.Join(lines[0:i], "\n")
+}
+
+func TestPrint(t *testing.T) {
+	var buf bytes.Buffer
+	for _, test := range tests {
+		buf.Reset()
+		if _, err := Fprint(&buf, nil, test.x, nil); err != nil {
+			t.Errorf("Fprint failed: %s", err)
+		}
+		if s, ts := trim(buf.String()), trim(test.s); s != ts {
+			t.Errorf("got:\n%s\nexpected:\n%s\n", s, ts)
+		}
+	}
+}
diff --git a/src/pkg/go/ast/resolve.go b/src/pkg/go/ast/resolve.go
new file mode 100644
index 000000000..3927a799e
--- /dev/null
+++ b/src/pkg/go/ast/resolve.go
@@ -0,0 +1,174 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements NewPackage.
+
+package ast
+
+import (
+	"fmt"
+	"go/scanner"
+	"go/token"
+	"os"
+	"strconv"
+)
+
+type pkgBuilder struct {
+	scanner.ErrorVector
+	fset *token.FileSet
+}
+
+func (p *pkgBuilder) error(pos token.Pos, msg string) {
+	p.Error(p.fset.Position(pos), msg)
+}
+
+func (p *pkgBuilder) errorf(pos token.Pos, format string, args ...interface{}) {
+	p.error(pos, fmt.Sprintf(format, args...))
+}
+
+func (p *pkgBuilder) declare(scope, altScope *Scope, obj *Object) {
+	alt := scope.Insert(obj)
+	if alt == nil && altScope != nil {
+		// see if there is a conflicting declaration in altScope
+		alt = altScope.Lookup(obj.Name)
+	}
+	if alt != nil {
+		prevDecl := ""
+		if pos := alt.Pos(); pos.IsValid() {
+			prevDecl = fmt.Sprintf("\n\tprevious declaration at %s", p.fset.Position(pos))
+		}
+		p.error(obj.Pos(), fmt.Sprintf("%s redeclared in this block%s", obj.Name, prevDecl))
+	}
+}
+
+func resolve(scope *Scope, ident *Ident) bool {
+	for ; scope != nil; scope = scope.Outer {
+		if obj := scope.Lookup(ident.Name); obj != nil {
+			ident.Obj = obj
+			return true
+		}
+	}
+	return false
+}
+
+// An Importer resolves import paths to package Objects.
+// The imports map records the packages already imported,
+// indexed by package id (canonical import path).
+// An Importer must determine the canonical import path and
+// check the map to see if it is already present in the imports map.
+// If so, the Importer can return the map entry.  Otherwise, the
+// Importer should load the package data for the given path into 
+// a new *Object (pkg), record pkg in the imports map, and then
+// return pkg.
+type Importer func(imports map[string]*Object, path string) (pkg *Object, err os.Error)
+
+// NewPackage creates a new Package node from a set of File nodes. It resolves
+// unresolved identifiers across files and updates each file's Unresolved list
+// accordingly. If a non-nil importer and universe scope are provided, they are
+// used to resolve identifiers not declared in any of the package files. Any
+// remaining unresolved identifiers are reported as undeclared. If the files
+// belong to different packages, one package name is selected and files with
+// different package names are reported and then ignored.
+// The result is a package node and a scanner.ErrorList if there were errors.
+//
+func NewPackage(fset *token.FileSet, files map[string]*File, importer Importer, universe *Scope) (*Package, os.Error) {
+	var p pkgBuilder
+	p.fset = fset
+
+	// complete package scope
+	pkgName := ""
+	pkgScope := NewScope(universe)
+	for _, file := range files {
+		// package names must match
+		switch name := file.Name.Name; {
+		case pkgName == "":
+			pkgName = name
+		case name != pkgName:
+			p.errorf(file.Package, "package %s; expected %s", name, pkgName)
+			continue // ignore this file
+		}
+
+		// collect top-level file objects in package scope
+		for _, obj := range file.Scope.Objects {
+			p.declare(pkgScope, nil, obj)
+		}
+	}
+
+	// package global mapping of imported package ids to package objects
+	imports := make(map[string]*Object)
+
+	// complete file scopes with imports and resolve identifiers
+	for _, file := range files {
+		// ignore file if it belongs to a different package
+		// (error has already been reported)
+		if file.Name.Name != pkgName {
+			continue
+		}
+
+		// build file scope by processing all imports
+		importErrors := false
+		fileScope := NewScope(pkgScope)
+		for _, spec := range file.Imports {
+			if importer == nil {
+				importErrors = true
+				continue
+			}
+			path, _ := strconv.Unquote(string(spec.Path.Value))
+			pkg, err := importer(imports, path)
+			if err != nil {
+				p.errorf(spec.Path.Pos(), "could not import %s (%s)", path, err)
+				importErrors = true
+				continue
+			}
+			// TODO(gri) If a local package name != "." is provided,
+			// global identifier resolution could proceed even if the
+			// import failed. Consider adjusting the logic here a bit.
+
+			// local name overrides imported package name
+			name := pkg.Name
+			if spec.Name != nil {
+				name = spec.Name.Name
+			}
+
+			// add import to file scope
+			if name == "." {
+				// merge imported scope with file scope
+				for _, obj := range pkg.Data.(*Scope).Objects {
+					p.declare(fileScope, pkgScope, obj)
+				}
+			} else {
+				// declare imported package object in file scope
+				// (do not re-use pkg in the file scope but create
+				// a new object instead; the Decl field is different
+				// for different files)
+				obj := NewObj(Pkg, name)
+				obj.Decl = spec
+				obj.Data = pkg.Data
+				p.declare(fileScope, pkgScope, obj)
+			}
+		}
+
+		// resolve identifiers
+		if importErrors {
+			// don't use the universe scope without correct imports
+			// (objects in the universe may be shadowed by imports;
+			// with missing imports, identifiers might get resolved
+			// incorrectly to universe objects)
+			pkgScope.Outer = nil
+		}
+		i := 0
+		for _, ident := range file.Unresolved {
+			if !resolve(fileScope, ident) {
+				p.errorf(ident.Pos(), "undeclared name: %s", ident.Name)
+				file.Unresolved[i] = ident
+				i++
+			}
+
+		}
+		file.Unresolved = file.Unresolved[0:i]
+		pkgScope.Outer = universe // reset universe scope
+	}
+
+	return &Package{pkgName, pkgScope, imports, files}, p.GetError(scanner.Sorted)
+}
diff --git a/src/pkg/go/ast/scope.go b/src/pkg/go/ast/scope.go
new file mode 100644
index 000000000..92e366980
--- /dev/null
+++ b/src/pkg/go/ast/scope.go
@@ -0,0 +1,156 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements scopes and the objects they contain.
+
+package ast
+
+import (
+	"bytes"
+	"fmt"
+	"go/token"
+)
+
+// A Scope maintains the set of named language entities declared
+// in the scope and a link to the immediately surrounding (outer)
+// scope.
+//
+type Scope struct {
+	Outer   *Scope
+	Objects map[string]*Object
+}
+
+// NewScope creates a new scope nested in the outer scope.
+func NewScope(outer *Scope) *Scope {
+	const n = 4 // initial scope capacity
+	return &Scope{outer, make(map[string]*Object, n)}
+}
+
+// Lookup returns the object with the given name if it is
+// found in scope s, otherwise it returns nil. Outer scopes
+// are ignored.
+//
+func (s *Scope) Lookup(name string) *Object {
+	return s.Objects[name]
+}
+
+// Insert attempts to insert a named object obj into the scope s.
+// If the scope already contains an object alt with the same name,
+// Insert leaves the scope unchanged and returns alt. Otherwise
+// it inserts obj and returns nil."
+//
+func (s *Scope) Insert(obj *Object) (alt *Object) {
+	if alt = s.Objects[obj.Name]; alt == nil {
+		s.Objects[obj.Name] = obj
+	}
+	return
+}
+
+// Debugging support
+func (s *Scope) String() string {
+	var buf bytes.Buffer
+	fmt.Fprintf(&buf, "scope %p {", s)
+	if s != nil && len(s.Objects) > 0 {
+		fmt.Fprintln(&buf)
+		for _, obj := range s.Objects {
+			fmt.Fprintf(&buf, "\t%s %s\n", obj.Kind, obj.Name)
+		}
+	}
+	fmt.Fprintf(&buf, "}\n")
+	return buf.String()
+}
+
+// ----------------------------------------------------------------------------
+// Objects
+
+// TODO(gri) Consider replacing the Object struct with an interface
+//           and a corresponding set of object implementations.
+
+// An Object describes a named language entity such as a package,
+// constant, type, variable, function (incl. methods), or label.
+//
+// The Data fields contains object-specific data:
+//
+//	Kind    Data type    Data value
+//	Pkg	*Scope       package scope
+//	Con     int          iota for the respective declaration
+//	Con     != nil       constant value
+//
+type Object struct {
+	Kind ObjKind
+	Name string      // declared name
+	Decl interface{} // corresponding Field, XxxSpec, FuncDecl, or LabeledStmt; or nil
+	Data interface{} // object-specific data; or nil
+	Type interface{} // place holder for type information; may be nil
+}
+
+// NewObj creates a new object of a given kind and name.
+func NewObj(kind ObjKind, name string) *Object {
+	return &Object{Kind: kind, Name: name}
+}
+
+// Pos computes the source position of the declaration of an object name.
+// The result may be an invalid position if it cannot be computed
+// (obj.Decl may be nil or not correct).
+func (obj *Object) Pos() token.Pos {
+	name := obj.Name
+	switch d := obj.Decl.(type) {
+	case *Field:
+		for _, n := range d.Names {
+			if n.Name == name {
+				return n.Pos()
+			}
+		}
+	case *ImportSpec:
+		if d.Name != nil && d.Name.Name == name {
+			return d.Name.Pos()
+		}
+		return d.Path.Pos()
+	case *ValueSpec:
+		for _, n := range d.Names {
+			if n.Name == name {
+				return n.Pos()
+			}
+		}
+	case *TypeSpec:
+		if d.Name.Name == name {
+			return d.Name.Pos()
+		}
+	case *FuncDecl:
+		if d.Name.Name == name {
+			return d.Name.Pos()
+		}
+	case *LabeledStmt:
+		if d.Label.Name == name {
+			return d.Label.Pos()
+		}
+	}
+	return token.NoPos
+}
+
+// ObKind describes what an object represents.
+type ObjKind int
+
+// The list of possible Object kinds.
+const (
+	Bad ObjKind = iota // for error handling
+	Pkg                // package
+	Con                // constant
+	Typ                // type
+	Var                // variable
+	Fun                // function or method
+	Lbl                // label
+)
+
+var objKindStrings = [...]string{
+	Bad: "bad",
+	Pkg: "package",
+	Con: "const",
+	Typ: "type",
+	Var: "var",
+	Fun: "func",
+	Lbl: "label",
+}
+
+func (kind ObjKind) String() string { return objKindStrings[kind] }
diff --git a/src/pkg/go/ast/walk.go b/src/pkg/go/ast/walk.go
new file mode 100644
index 000000000..181cfd149
--- /dev/null
+++ b/src/pkg/go/ast/walk.go
@@ -0,0 +1,382 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package ast
+
+import "fmt"
+
+// A Visitor's Visit method is invoked for each node encountered by Walk.
+// If the result visitor w is not nil, Walk visits each of the children
+// of node with the visitor w, followed by a call of w.Visit(nil).
+type Visitor interface {
+	Visit(node Node) (w Visitor)
+}
+
+// Helper functions for common node lists. They may be empty.
+
+func walkIdentList(v Visitor, list []*Ident) {
+	for _, x := range list {
+		Walk(v, x)
+	}
+}
+
+func walkExprList(v Visitor, list []Expr) {
+	for _, x := range list {
+		Walk(v, x)
+	}
+}
+
+func walkStmtList(v Visitor, list []Stmt) {
+	for _, x := range list {
+		Walk(v, x)
+	}
+}
+
+func walkDeclList(v Visitor, list []Decl) {
+	for _, x := range list {
+		Walk(v, x)
+	}
+}
+
+// TODO(gri): Investigate if providing a closure to Walk leads to
+//            simpler use (and may help eliminate Inspect in turn).
+
+// Walk traverses an AST in depth-first order: It starts by calling
+// v.Visit(node); node must not be nil. If the visitor w returned by
+// v.Visit(node) is not nil, Walk is invoked recursively with visitor
+// w for each of the non-nil children of node, followed by a call of
+// w.Visit(nil).
+//
+func Walk(v Visitor, node Node) {
+	if v = v.Visit(node); v == nil {
+		return
+	}
+
+	// walk children
+	// (the order of the cases matches the order
+	// of the corresponding node types in ast.go)
+	switch n := node.(type) {
+	// Comments and fields
+	case *Comment:
+		// nothing to do
+
+	case *CommentGroup:
+		for _, c := range n.List {
+			Walk(v, c)
+		}
+
+	case *Field:
+		if n.Doc != nil {
+			Walk(v, n.Doc)
+		}
+		walkIdentList(v, n.Names)
+		Walk(v, n.Type)
+		if n.Tag != nil {
+			Walk(v, n.Tag)
+		}
+		if n.Comment != nil {
+			Walk(v, n.Comment)
+		}
+
+	case *FieldList:
+		for _, f := range n.List {
+			Walk(v, f)
+		}
+
+	// Expressions
+	case *BadExpr, *Ident, *BasicLit:
+		// nothing to do
+
+	case *Ellipsis:
+		if n.Elt != nil {
+			Walk(v, n.Elt)
+		}
+
+	case *FuncLit:
+		Walk(v, n.Type)
+		Walk(v, n.Body)
+
+	case *CompositeLit:
+		if n.Type != nil {
+			Walk(v, n.Type)
+		}
+		walkExprList(v, n.Elts)
+
+	case *ParenExpr:
+		Walk(v, n.X)
+
+	case *SelectorExpr:
+		Walk(v, n.X)
+		Walk(v, n.Sel)
+
+	case *IndexExpr:
+		Walk(v, n.X)
+		Walk(v, n.Index)
+
+	case *SliceExpr:
+		Walk(v, n.X)
+		if n.Low != nil {
+			Walk(v, n.Low)
+		}
+		if n.High != nil {
+			Walk(v, n.High)
+		}
+
+	case *TypeAssertExpr:
+		Walk(v, n.X)
+		if n.Type != nil {
+			Walk(v, n.Type)
+		}
+
+	case *CallExpr:
+		Walk(v, n.Fun)
+		walkExprList(v, n.Args)
+
+	case *StarExpr:
+		Walk(v, n.X)
+
+	case *UnaryExpr:
+		Walk(v, n.X)
+
+	case *BinaryExpr:
+		Walk(v, n.X)
+		Walk(v, n.Y)
+
+	case *KeyValueExpr:
+		Walk(v, n.Key)
+		Walk(v, n.Value)
+
+	// Types
+	case *ArrayType:
+		if n.Len != nil {
+			Walk(v, n.Len)
+		}
+		Walk(v, n.Elt)
+
+	case *StructType:
+		Walk(v, n.Fields)
+
+	case *FuncType:
+		Walk(v, n.Params)
+		if n.Results != nil {
+			Walk(v, n.Results)
+		}
+
+	case *InterfaceType:
+		Walk(v, n.Methods)
+
+	case *MapType:
+		Walk(v, n.Key)
+		Walk(v, n.Value)
+
+	case *ChanType:
+		Walk(v, n.Value)
+
+	// Statements
+	case *BadStmt:
+		// nothing to do
+
+	case *DeclStmt:
+		Walk(v, n.Decl)
+
+	case *EmptyStmt:
+		// nothing to do
+
+	case *LabeledStmt:
+		Walk(v, n.Label)
+		Walk(v, n.Stmt)
+
+	case *ExprStmt:
+		Walk(v, n.X)
+
+	case *SendStmt:
+		Walk(v, n.Chan)
+		Walk(v, n.Value)
+
+	case *IncDecStmt:
+		Walk(v, n.X)
+
+	case *AssignStmt:
+		walkExprList(v, n.Lhs)
+		walkExprList(v, n.Rhs)
+
+	case *GoStmt:
+		Walk(v, n.Call)
+
+	case *DeferStmt:
+		Walk(v, n.Call)
+
+	case *ReturnStmt:
+		walkExprList(v, n.Results)
+
+	case *BranchStmt:
+		if n.Label != nil {
+			Walk(v, n.Label)
+		}
+
+	case *BlockStmt:
+		walkStmtList(v, n.List)
+
+	case *IfStmt:
+		if n.Init != nil {
+			Walk(v, n.Init)
+		}
+		Walk(v, n.Cond)
+		Walk(v, n.Body)
+		if n.Else != nil {
+			Walk(v, n.Else)
+		}
+
+	case *CaseClause:
+		walkExprList(v, n.List)
+		walkStmtList(v, n.Body)
+
+	case *SwitchStmt:
+		if n.Init != nil {
+			Walk(v, n.Init)
+		}
+		if n.Tag != nil {
+			Walk(v, n.Tag)
+		}
+		Walk(v, n.Body)
+
+	case *TypeSwitchStmt:
+		if n.Init != nil {
+			Walk(v, n.Init)
+		}
+		Walk(v, n.Assign)
+		Walk(v, n.Body)
+
+	case *CommClause:
+		if n.Comm != nil {
+			Walk(v, n.Comm)
+		}
+		walkStmtList(v, n.Body)
+
+	case *SelectStmt:
+		Walk(v, n.Body)
+
+	case *ForStmt:
+		if n.Init != nil {
+			Walk(v, n.Init)
+		}
+		if n.Cond != nil {
+			Walk(v, n.Cond)
+		}
+		if n.Post != nil {
+			Walk(v, n.Post)
+		}
+		Walk(v, n.Body)
+
+	case *RangeStmt:
+		Walk(v, n.Key)
+		if n.Value != nil {
+			Walk(v, n.Value)
+		}
+		Walk(v, n.X)
+		Walk(v, n.Body)
+
+	// Declarations
+	case *ImportSpec:
+		if n.Doc != nil {
+			Walk(v, n.Doc)
+		}
+		if n.Name != nil {
+			Walk(v, n.Name)
+		}
+		Walk(v, n.Path)
+		if n.Comment != nil {
+			Walk(v, n.Comment)
+		}
+
+	case *ValueSpec:
+		if n.Doc != nil {
+			Walk(v, n.Doc)
+		}
+		walkIdentList(v, n.Names)
+		if n.Type != nil {
+			Walk(v, n.Type)
+		}
+		walkExprList(v, n.Values)
+		if n.Comment != nil {
+			Walk(v, n.Comment)
+		}
+
+	case *TypeSpec:
+		if n.Doc != nil {
+			Walk(v, n.Doc)
+		}
+		Walk(v, n.Name)
+		Walk(v, n.Type)
+		if n.Comment != nil {
+			Walk(v, n.Comment)
+		}
+
+	case *BadDecl:
+		// nothing to do
+
+	case *GenDecl:
+		if n.Doc != nil {
+			Walk(v, n.Doc)
+		}
+		for _, s := range n.Specs {
+			Walk(v, s)
+		}
+
+	case *FuncDecl:
+		if n.Doc != nil {
+			Walk(v, n.Doc)
+		}
+		if n.Recv != nil {
+			Walk(v, n.Recv)
+		}
+		Walk(v, n.Name)
+		Walk(v, n.Type)
+		if n.Body != nil {
+			Walk(v, n.Body)
+		}
+
+	// Files and packages
+	case *File:
+		if n.Doc != nil {
+			Walk(v, n.Doc)
+		}
+		Walk(v, n.Name)
+		walkDeclList(v, n.Decls)
+		for _, g := range n.Comments {
+			Walk(v, g)
+		}
+		// don't walk n.Comments - they have been
+		// visited already through the individual
+		// nodes
+
+	case *Package:
+		for _, f := range n.Files {
+			Walk(v, f)
+		}
+
+	default:
+		fmt.Printf("ast.Walk: unexpected node type %T", n)
+		panic("ast.Walk")
+	}
+
+	v.Visit(nil)
+}
+
+type inspector func(Node) bool
+
+func (f inspector) Visit(node Node) Visitor {
+	if f(node) {
+		return f
+	}
+	return nil
+}
+
+// Inspect traverses an AST in depth-first order: It starts by calling
+// f(node); node must not be nil. If f returns true, Inspect invokes f
+// for all the non-nil children of node, recursively.
+//
+func Inspect(node Node, f func(Node) bool) {
+	Walk(inspector(f), node)
+}
diff --git a/src/pkg/go/build/Makefile b/src/pkg/go/build/Makefile
new file mode 100644
index 000000000..349e00e80
--- /dev/null
+++ b/src/pkg/go/build/Makefile
@@ -0,0 +1,22 @@
+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../Make.inc
+
+TARG=go/build
+GOFILES=\
+	build.go\
+	dir.go\
+	path.go\
+	syslist.go\
+
+CLEANFILES+=syslist.go pkgtest/_obj cmdtest/_obj cgotest/_obj
+
+include ../../../Make.pkg
+
+syslist.go: ../../../Make.inc Makefile
+	echo '// Generated automatically by make.' >$@
+	echo 'package build' >>$@
+	echo 'const goosList = "$(GOOS_LIST)"' >>$@
+	echo 'const goarchList = "$(GOARCH_LIST)"' >>$@
diff --git a/src/pkg/go/build/build.go b/src/pkg/go/build/build.go
new file mode 100644
index 000000000..97f92bfb6
--- /dev/null
+++ b/src/pkg/go/build/build.go
@@ -0,0 +1,444 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package build provides tools for building Go packages.
+package build
+
+import (
+	"bytes"
+	"exec"
+	"fmt"
+	"os"
+	"path/filepath"
+	"regexp"
+	"runtime"
+	"strings"
+)
+
+// Build produces a build Script for the given package.
+func Build(tree *Tree, pkg string, info *DirInfo) (*Script, os.Error) {
+	s := &Script{}
+	b := &build{
+		script: s,
+		path:   filepath.Join(tree.SrcDir(), pkg),
+	}
+	b.obj = b.abs("_obj") + string(filepath.Separator)
+
+	b.goarch = runtime.GOARCH
+	if g := os.Getenv("GOARCH"); g != "" {
+		b.goarch = g
+	}
+	var err os.Error
+	b.arch, err = ArchChar(b.goarch)
+	if err != nil {
+		return nil, err
+	}
+
+	// add import object files to list of Inputs
+	for _, pkg := range info.Imports {
+		t, p, err := FindTree(pkg)
+		if err != nil && err != ErrNotFound {
+			// FindTree should always be able to suggest an import
+			// path and tree. The path must be malformed
+			// (for example, an absolute or relative path).
+			return nil, os.NewError("build: invalid import: " + pkg)
+		}
+		s.addInput(filepath.Join(t.PkgDir(), p+".a"))
+	}
+
+	// .go files to be built with gc
+	gofiles := b.abss(info.GoFiles...)
+	s.addInput(gofiles...)
+
+	var ofiles []string // object files to be linked or packed
+
+	// make build directory
+	b.mkdir(b.obj)
+	s.addIntermediate(b.obj)
+
+	// cgo
+	if len(info.CgoFiles) > 0 {
+		cgoFiles := b.abss(info.CgoFiles...)
+		s.addInput(cgoFiles...)
+		cgoCFiles := b.abss(info.CFiles...)
+		s.addInput(cgoCFiles...)
+		outGo, outObj := b.cgo(cgoFiles, cgoCFiles)
+		gofiles = append(gofiles, outGo...)
+		ofiles = append(ofiles, outObj...)
+		s.addIntermediate(outGo...)
+		s.addIntermediate(outObj...)
+	}
+
+	// compile
+	if len(gofiles) > 0 {
+		ofile := b.obj + "_go_." + b.arch
+		b.gc(ofile, gofiles...)
+		ofiles = append(ofiles, ofile)
+		s.addIntermediate(ofile)
+	}
+
+	// assemble
+	for _, sfile := range info.SFiles {
+		ofile := b.obj + sfile[:len(sfile)-1] + b.arch
+		sfile = b.abs(sfile)
+		s.addInput(sfile)
+		b.asm(ofile, sfile)
+		ofiles = append(ofiles, ofile)
+		s.addIntermediate(ofile)
+	}
+
+	if len(ofiles) == 0 {
+		return nil, os.NewError("make: no object files to build")
+	}
+
+	// choose target file
+	var targ string
+	if info.IsCommand() {
+		// use the last part of the import path as binary name
+		_, bin := filepath.Split(pkg)
+		if runtime.GOOS == "windows" {
+			bin += ".exe"
+		}
+		targ = filepath.Join(tree.BinDir(), bin)
+	} else {
+		targ = filepath.Join(tree.PkgDir(), pkg+".a")
+	}
+
+	// make target directory
+	targDir, _ := filepath.Split(targ)
+	b.mkdir(targDir)
+
+	// link binary or pack object
+	if info.IsCommand() {
+		b.ld(targ, ofiles...)
+	} else {
+		b.gopack(targ, ofiles...)
+	}
+	s.Output = append(s.Output, targ)
+
+	return b.script, nil
+}
+
+// A Script describes the build process for a Go package.
+// The Input, Intermediate, and Output fields are lists of absolute paths.
+type Script struct {
+	Cmd          []*Cmd
+	Input        []string
+	Intermediate []string
+	Output       []string
+}
+
+func (s *Script) addInput(file ...string) {
+	s.Input = append(s.Input, file...)
+}
+
+func (s *Script) addIntermediate(file ...string) {
+	s.Intermediate = append(s.Intermediate, file...)
+}
+
+// Run runs the Script's Cmds in order.
+func (s *Script) Run() os.Error {
+	for _, c := range s.Cmd {
+		if err := c.Run(); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
+// Stale returns true if the build's inputs are newer than its outputs.
+func (s *Script) Stale() bool {
+	var latest int64
+	// get latest mtime of outputs
+	for _, file := range s.Output {
+		fi, err := os.Stat(file)
+		if err != nil {
+			// any error reading output files means stale
+			return true
+		}
+		if m := fi.Mtime_ns; m > latest {
+			latest = m
+		}
+	}
+	for _, file := range s.Input {
+		fi, err := os.Stat(file)
+		if err != nil || fi.Mtime_ns > latest {
+			// any error reading input files means stale
+			// (attempt to rebuild to figure out why)
+			return true
+		}
+	}
+	return false
+}
+
+// Clean removes the Script's Intermediate files.
+// It tries to remove every file and returns the first error it encounters.
+func (s *Script) Clean() (err os.Error) {
+	// Reverse order so that directories get removed after the files they contain.
+	for i := len(s.Intermediate) - 1; i >= 0; i-- {
+		if e := os.Remove(s.Intermediate[i]); err == nil {
+			err = e
+		}
+	}
+	return
+}
+
+// Nuke removes the Script's Intermediate and Output files.
+// It tries to remove every file and returns the first error it encounters.
+func (s *Script) Nuke() (err os.Error) {
+	// Reverse order so that directories get removed after the files they contain.
+	for i := len(s.Output) - 1; i >= 0; i-- {
+		if e := os.Remove(s.Output[i]); err == nil {
+			err = e
+		}
+	}
+	if e := s.Clean(); err == nil {
+		err = e
+	}
+	return
+}
+
+// A Cmd describes an individual build command.
+type Cmd struct {
+	Args   []string // command-line
+	Stdout string   // write standard output to this file, "" is passthrough
+	Dir    string   // working directory
+	Env    []string // environment
+	Input  []string // file paths (dependencies)
+	Output []string // file paths
+}
+
+func (c *Cmd) String() string {
+	return strings.Join(c.Args, " ")
+}
+
+// Run executes the Cmd.
+func (c *Cmd) Run() os.Error {
+	if c.Args[0] == "mkdir" {
+		for _, p := range c.Output {
+			if err := os.MkdirAll(p, 0777); err != nil {
+				return fmt.Errorf("command %q: %v", c, err)
+			}
+		}
+		return nil
+	}
+	out := new(bytes.Buffer)
+	cmd := exec.Command(c.Args[0], c.Args[1:]...)
+	cmd.Dir = c.Dir
+	cmd.Env = c.Env
+	cmd.Stdout = out
+	cmd.Stderr = out
+	if c.Stdout != "" {
+		f, err := os.Create(c.Stdout)
+		if err != nil {
+			return err
+		}
+		defer f.Close()
+		cmd.Stdout = f
+	}
+	if err := cmd.Run(); err != nil {
+		return fmt.Errorf("command %q: %v\n%v", c, err, out)
+	}
+	return nil
+}
+
+// ArchChar returns the architecture character for the given goarch.
+// For example, ArchChar("amd64") returns "6".
+func ArchChar(goarch string) (string, os.Error) {
+	switch goarch {
+	case "386":
+		return "8", nil
+	case "amd64":
+		return "6", nil
+	case "arm":
+		return "5", nil
+	}
+	return "", os.NewError("unsupported GOARCH " + goarch)
+}
+
+type build struct {
+	script *Script
+	path   string
+	obj    string
+	goarch string
+	arch   string
+}
+
+func (b *build) abs(file string) string {
+	if filepath.IsAbs(file) {
+		return file
+	}
+	return filepath.Join(b.path, file)
+}
+
+func (b *build) abss(file ...string) []string {
+	s := make([]string, len(file))
+	for i, f := range file {
+		s[i] = b.abs(f)
+	}
+	return s
+}
+
+func (b *build) add(c Cmd) {
+	b.script.Cmd = append(b.script.Cmd, &c)
+}
+
+func (b *build) mkdir(name string) {
+	b.add(Cmd{
+		Args:   []string{"mkdir", "-p", name},
+		Output: []string{name},
+	})
+}
+
+func (b *build) gc(ofile string, gofiles ...string) {
+	gc := b.arch + "g"
+	args := append([]string{gc, "-o", ofile}, gcImportArgs...)
+	args = append(args, gofiles...)
+	b.add(Cmd{
+		Args:   args,
+		Input:  gofiles,
+		Output: []string{ofile},
+	})
+}
+
+func (b *build) asm(ofile string, sfile string) {
+	asm := b.arch + "a"
+	b.add(Cmd{
+		Args:   []string{asm, "-o", ofile, sfile},
+		Input:  []string{sfile},
+		Output: []string{ofile},
+	})
+}
+
+func (b *build) ld(targ string, ofiles ...string) {
+	ld := b.arch + "l"
+	args := append([]string{ld, "-o", targ}, ldImportArgs...)
+	args = append(args, ofiles...)
+	b.add(Cmd{
+		Args:   args,
+		Input:  ofiles,
+		Output: []string{targ},
+	})
+}
+
+func (b *build) gopack(targ string, ofiles ...string) {
+	b.add(Cmd{
+		Args:   append([]string{"gopack", "grc", targ}, ofiles...),
+		Input:  ofiles,
+		Output: []string{targ},
+	})
+}
+
+func (b *build) cc(ofile string, cfiles ...string) {
+	cc := b.arch + "c"
+	dir := fmt.Sprintf("%s_%s", runtime.GOOS, runtime.GOARCH)
+	inc := filepath.Join(runtime.GOROOT(), "pkg", dir)
+	args := []string{cc, "-FVw", "-I", inc, "-o", ofile}
+	b.add(Cmd{
+		Args:   append(args, cfiles...),
+		Input:  cfiles,
+		Output: []string{ofile},
+	})
+}
+
+func (b *build) gccCompile(ofile, cfile string) {
+	b.add(Cmd{
+		Args:   b.gccArgs("-o", ofile, "-c", cfile),
+		Input:  []string{cfile},
+		Output: []string{ofile},
+	})
+}
+
+func (b *build) gccLink(ofile string, ofiles ...string) {
+	b.add(Cmd{
+		Args:   append(b.gccArgs("-o", ofile), ofiles...),
+		Input:  ofiles,
+		Output: []string{ofile},
+	})
+}
+
+func (b *build) gccArgs(args ...string) []string {
+	// TODO(adg): HOST_CC
+	a := []string{"gcc", "-I", b.path, "-g", "-fPIC", "-O2"}
+	switch b.arch {
+	case "8":
+		a = append(a, "-m32")
+	case "6":
+		a = append(a, "-m64")
+	}
+	return append(a, args...)
+}
+
+var cgoRe = regexp.MustCompile(`[/\\:]`)
+
+func (b *build) cgo(cgofiles, cgocfiles []string) (outGo, outObj []string) {
+	// cgo
+	// TODO(adg): CGOPKGPATH
+	// TODO(adg): CGO_FLAGS
+	gofiles := []string{b.obj + "_cgo_gotypes.go"}
+	cfiles := []string{b.obj + "_cgo_main.c", b.obj + "_cgo_export.c"}
+	for _, fn := range cgofiles {
+		f := b.obj + cgoRe.ReplaceAllString(fn[:len(fn)-2], "_")
+		gofiles = append(gofiles, f+"cgo1.go")
+		cfiles = append(cfiles, f+"cgo2.c")
+	}
+	defunC := b.obj + "_cgo_defun.c"
+	output := append([]string{defunC}, cfiles...)
+	output = append(output, gofiles...)
+	b.add(Cmd{
+		Args:   append([]string{"cgo", "--"}, cgofiles...),
+		Dir:    b.path,
+		Env:    append(os.Environ(), "GOARCH="+b.goarch),
+		Input:  cgofiles,
+		Output: output,
+	})
+	outGo = append(outGo, gofiles...)
+	exportH := filepath.Join(b.path, "_cgo_export.h")
+	b.script.addIntermediate(defunC, exportH, b.obj+"_cgo_flags")
+	b.script.addIntermediate(cfiles...)
+
+	// cc _cgo_defun.c
+	defunObj := b.obj + "_cgo_defun." + b.arch
+	b.cc(defunObj, defunC)
+	outObj = append(outObj, defunObj)
+
+	// gcc
+	linkobj := make([]string, 0, len(cfiles))
+	for _, cfile := range cfiles {
+		ofile := cfile[:len(cfile)-1] + "o"
+		b.gccCompile(ofile, cfile)
+		linkobj = append(linkobj, ofile)
+		if !strings.HasSuffix(ofile, "_cgo_main.o") {
+			outObj = append(outObj, ofile)
+		} else {
+			b.script.addIntermediate(ofile)
+		}
+	}
+	for _, cfile := range cgocfiles {
+		ofile := b.obj + cgoRe.ReplaceAllString(cfile[:len(cfile)-1], "_") + "o"
+		b.gccCompile(ofile, cfile)
+		linkobj = append(linkobj, ofile)
+		outObj = append(outObj, ofile)
+	}
+	dynObj := b.obj + "_cgo_.o"
+	b.gccLink(dynObj, linkobj...)
+	b.script.addIntermediate(dynObj)
+
+	// cgo -dynimport
+	importC := b.obj + "_cgo_import.c"
+	b.add(Cmd{
+		Args:   []string{"cgo", "-dynimport", dynObj},
+		Stdout: importC,
+		Input:  []string{dynObj},
+		Output: []string{importC},
+	})
+	b.script.addIntermediate(importC)
+
+	// cc _cgo_import.ARCH
+	importObj := b.obj + "_cgo_import." + b.arch
+	b.cc(importObj, importC)
+	outObj = append(outObj, importObj)
+
+	return
+}
diff --git a/src/pkg/go/build/build_test.go b/src/pkg/go/build/build_test.go
new file mode 100644
index 000000000..e59d87672
--- /dev/null
+++ b/src/pkg/go/build/build_test.go
@@ -0,0 +1,61 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package build
+
+import (
+	"exec"
+	"path/filepath"
+	"testing"
+)
+
+var buildPkgs = []string{
+	"go/build/pkgtest",
+	"go/build/cmdtest",
+	"go/build/cgotest",
+}
+
+const cmdtestOutput = "3"
+
+func TestBuild(t *testing.T) {
+	for _, pkg := range buildPkgs {
+		tree := Path[0] // Goroot
+		dir := filepath.Join(tree.SrcDir(), pkg)
+
+		info, err := ScanDir(dir, true)
+		if err != nil {
+			t.Error("ScanDir:", err)
+			continue
+		}
+
+		s, err := Build(tree, pkg, info)
+		if err != nil {
+			t.Error("Build:", err)
+			continue
+		}
+
+		if err := s.Run(); err != nil {
+			t.Error("Run:", err)
+			continue
+		}
+
+		if pkg == "go/build/cmdtest" {
+			bin := s.Output[0]
+			b, err := exec.Command(bin).CombinedOutput()
+			if err != nil {
+				t.Errorf("exec: %s: %v", bin, err)
+				continue
+			}
+			if string(b) != cmdtestOutput {
+				t.Errorf("cmdtest output: %s want: %s", b, cmdtestOutput)
+			}
+		}
+
+		defer func(s *Script) {
+			if err := s.Nuke(); err != nil {
+				t.Errorf("nuking: %v", err)
+			}
+		}(s)
+	}
+}
diff --git a/src/pkg/go/build/cgotest/cgotest.c b/src/pkg/go/build/cgotest/cgotest.c
new file mode 100644
index 000000000..b13acb227
--- /dev/null
+++ b/src/pkg/go/build/cgotest/cgotest.c
@@ -0,0 +1,9 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+int
+Add(int x, int y, int *sum)
+{
+	sum = x+y;
+}
diff --git a/src/pkg/go/build/cgotest/cgotest.go b/src/pkg/go/build/cgotest/cgotest.go
new file mode 100644
index 000000000..93bbf0688
--- /dev/null
+++ b/src/pkg/go/build/cgotest/cgotest.go
@@ -0,0 +1,19 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package cgotest
+
+/*
+char* greeting = "hello, world";
+*/
+// #include "cgotest.h"
+import "C"
+import "unsafe"
+
+var Greeting = C.GoString(C.greeting)
+
+func DoAdd(x, y int) (sum int) {
+	C.Add(C.int(x), C.int(y), (*C.int)(unsafe.Pointer(&sum)))
+	return
+}
diff --git a/src/pkg/go/build/cgotest/cgotest.h b/src/pkg/go/build/cgotest/cgotest.h
new file mode 100644
index 000000000..9c73643b6
--- /dev/null
+++ b/src/pkg/go/build/cgotest/cgotest.h
@@ -0,0 +1,5 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+extern int Add(int, int, int *);
diff --git a/src/pkg/go/build/cmdtest/main.go b/src/pkg/go/build/cmdtest/main.go
new file mode 100644
index 000000000..bed4f485a
--- /dev/null
+++ b/src/pkg/go/build/cmdtest/main.go
@@ -0,0 +1,12 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package main
+
+import "go/build/pkgtest"
+
+func main() {
+	pkgtest.Foo()
+	print(int(pkgtest.Sqrt(9)))
+}
diff --git a/src/pkg/go/build/dir.go b/src/pkg/go/build/dir.go
new file mode 100644
index 000000000..e0000b534
--- /dev/null
+++ b/src/pkg/go/build/dir.go
@@ -0,0 +1,172 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package build
+
+import (
+	"go/parser"
+	"go/token"
+	"log"
+	"os"
+	"path/filepath"
+	"strconv"
+	"strings"
+	"runtime"
+)
+
+type DirInfo struct {
+	GoFiles  []string // .go files in dir (excluding CgoFiles)
+	CgoFiles []string // .go files that import "C"
+	CFiles   []string // .c files in dir
+	SFiles   []string // .s files in dir
+	Imports  []string // All packages imported by goFiles
+	PkgName  string   // Name of package in dir
+}
+
+func (d *DirInfo) IsCommand() bool {
+	return d.PkgName == "main"
+}
+
+// ScanDir returns a structure with details about the Go content found
+// in the given directory. The file lists exclude:
+//
+//	- files in package main (unless allowMain is true)
+//	- files in package documentation
+//	- files ending in _test.go
+// 	- files starting with _ or .
+//
+// Only files that satisfy the goodOSArch function are included.
+func ScanDir(dir string, allowMain bool) (info *DirInfo, err os.Error) {
+	f, err := os.Open(dir)
+	if err != nil {
+		return nil, err
+	}
+	dirs, err := f.Readdir(-1)
+	f.Close()
+	if err != nil {
+		return nil, err
+	}
+
+	var di DirInfo
+	imported := make(map[string]bool)
+	fset := token.NewFileSet()
+	for i := range dirs {
+		d := &dirs[i]
+		if strings.HasPrefix(d.Name, "_") ||
+			strings.HasPrefix(d.Name, ".") {
+			continue
+		}
+		if !goodOSArch(d.Name) {
+			continue
+		}
+
+		switch filepath.Ext(d.Name) {
+		case ".go":
+			if strings.HasSuffix(d.Name, "_test.go") {
+				continue
+			}
+		case ".c":
+			di.CFiles = append(di.CFiles, d.Name)
+			continue
+		case ".s":
+			di.SFiles = append(di.SFiles, d.Name)
+			continue
+		default:
+			continue
+		}
+
+		filename := filepath.Join(dir, d.Name)
+		pf, err := parser.ParseFile(fset, filename, nil, parser.ImportsOnly)
+		if err != nil {
+			return nil, err
+		}
+		s := string(pf.Name.Name)
+		if s == "main" && !allowMain {
+			continue
+		}
+		if s == "documentation" {
+			continue
+		}
+		if di.PkgName == "" {
+			di.PkgName = s
+		} else if di.PkgName != s {
+			// Only if all files in the directory are in package main
+			// do we return PkgName=="main".
+			// A mix of main and another package reverts
+			// to the original (allowMain=false) behaviour.
+			if s == "main" || di.PkgName == "main" {
+				return ScanDir(dir, false)
+			}
+			return nil, os.NewError("multiple package names in " + dir)
+		}
+		isCgo := false
+		for _, spec := range pf.Imports {
+			quoted := string(spec.Path.Value)
+			path, err := strconv.Unquote(quoted)
+			if err != nil {
+				log.Panicf("%s: parser returned invalid quoted string: <%s>", filename, quoted)
+			}
+			imported[path] = true
+			if path == "C" {
+				isCgo = true
+			}
+		}
+		if isCgo {
+			di.CgoFiles = append(di.CgoFiles, d.Name)
+		} else {
+			di.GoFiles = append(di.GoFiles, d.Name)
+		}
+	}
+	di.Imports = make([]string, len(imported))
+	i := 0
+	for p := range imported {
+		di.Imports[i] = p
+		i++
+	}
+	return &di, nil
+}
+
+// goodOSArch returns false if the filename contains a $GOOS or $GOARCH
+// suffix which does not match the current system.
+// The recognized filename formats are:
+//
+//     name_$(GOOS).*
+//     name_$(GOARCH).*
+//     name_$(GOOS)_$(GOARCH).*
+//
+func goodOSArch(filename string) bool {
+	if dot := strings.Index(filename, "."); dot != -1 {
+		filename = filename[:dot]
+	}
+	l := strings.Split(filename, "_")
+	n := len(l)
+	if n == 0 {
+		return true
+	}
+	if good, known := goodOS[l[n-1]]; known {
+		return good
+	}
+	if good, known := goodArch[l[n-1]]; known {
+		if !good || n < 2 {
+			return false
+		}
+		good, known = goodOS[l[n-2]]
+		return good || !known
+	}
+	return true
+}
+
+var goodOS = make(map[string]bool)
+var goodArch = make(map[string]bool)
+
+func init() {
+	goodOS = make(map[string]bool)
+	goodArch = make(map[string]bool)
+	for _, v := range strings.Fields(goosList) {
+		goodOS[v] = v == runtime.GOOS
+	}
+	for _, v := range strings.Fields(goarchList) {
+		goodArch[v] = v == runtime.GOARCH
+	}
+}
diff --git a/src/pkg/go/build/path.go b/src/pkg/go/build/path.go
new file mode 100644
index 000000000..e39b5f8fa
--- /dev/null
+++ b/src/pkg/go/build/path.go
@@ -0,0 +1,182 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package build
+
+import (
+	"fmt"
+	"log"
+	"os"
+	"path/filepath"
+	"runtime"
+)
+
+// Path is a validated list of Trees derived from $GOROOT and $GOPATH at init.
+var Path []*Tree
+
+// Tree describes a Go source tree, either $GOROOT or one from $GOPATH.
+type Tree struct {
+	Path   string
+	Goroot bool
+}
+
+func newTree(p string) (*Tree, os.Error) {
+	if !filepath.IsAbs(p) {
+		return nil, os.NewError("must be absolute")
+	}
+	ep, err := filepath.EvalSymlinks(p)
+	if err != nil {
+		return nil, err
+	}
+	return &Tree{Path: ep}, nil
+}
+
+// SrcDir returns the tree's package source directory.
+func (t *Tree) SrcDir() string {
+	if t.Goroot {
+		return filepath.Join(t.Path, "src", "pkg")
+	}
+	return filepath.Join(t.Path, "src")
+}
+
+// PkgDir returns the tree's package object directory.
+func (t *Tree) PkgDir() string {
+	goos, goarch := runtime.GOOS, runtime.GOARCH
+	if e := os.Getenv("GOOS"); e != "" {
+		goos = e
+	}
+	if e := os.Getenv("GOARCH"); e != "" {
+		goarch = e
+	}
+	return filepath.Join(t.Path, "pkg", goos+"_"+goarch)
+}
+
+// BinDir returns the tree's binary executable directory.
+func (t *Tree) BinDir() string {
+	if t.Goroot {
+		if gobin := os.Getenv("GOBIN"); gobin != "" {
+			return gobin
+		}
+	}
+	return filepath.Join(t.Path, "bin")
+}
+
+// HasSrc returns whether the given package's
+// source can be found inside this Tree.
+func (t *Tree) HasSrc(pkg string) bool {
+	fi, err := os.Stat(filepath.Join(t.SrcDir(), pkg))
+	if err != nil {
+		return false
+	}
+	return fi.IsDirectory()
+}
+
+// HasPkg returns whether the given package's
+// object file can be found inside this Tree.
+func (t *Tree) HasPkg(pkg string) bool {
+	fi, err := os.Stat(filepath.Join(t.PkgDir(), pkg+".a"))
+	if err != nil {
+		return false
+	}
+	return fi.IsRegular()
+	// TODO(adg): check object version is consistent
+}
+
+var (
+	ErrNotFound     = os.NewError("go/build: package could not be found locally")
+	ErrTreeNotFound = os.NewError("go/build: no valid GOROOT or GOPATH could be found")
+)
+
+// FindTree takes an import or filesystem path and returns the
+// tree where the package source should be and the package import path.
+func FindTree(path string) (tree *Tree, pkg string, err os.Error) {
+	if isLocalPath(path) {
+		if path, err = filepath.Abs(path); err != nil {
+			return
+		}
+		if path, err = filepath.EvalSymlinks(path); err != nil {
+			return
+		}
+		for _, t := range Path {
+			tpath := t.SrcDir() + string(filepath.Separator)
+			if !filepath.HasPrefix(path, tpath) {
+				continue
+			}
+			tree = t
+			pkg = path[len(tpath):]
+			return
+		}
+		err = fmt.Errorf("path %q not inside a GOPATH", path)
+		return
+	}
+	tree = defaultTree
+	pkg = path
+	for _, t := range Path {
+		if t.HasSrc(pkg) {
+			tree = t
+			return
+		}
+	}
+	if tree == nil {
+		err = ErrTreeNotFound
+	} else {
+		err = ErrNotFound
+	}
+	return
+}
+
+// isLocalPath returns whether the given path is local (/foo ./foo ../foo . ..)
+// Windows paths that starts with drive letter (c:\foo c:foo) are considered local.
+func isLocalPath(s string) bool {
+	const sep = string(filepath.Separator)
+	return s == "." || s == ".." ||
+		filepath.HasPrefix(s, sep) ||
+		filepath.HasPrefix(s, "."+sep) || filepath.HasPrefix(s, ".."+sep) ||
+		filepath.VolumeName(s) != ""
+}
+
+var (
+	// argument lists used by the build's gc and ld methods
+	gcImportArgs []string
+	ldImportArgs []string
+
+	// default tree for remote packages
+	defaultTree *Tree
+)
+
+// set up Path: parse and validate GOROOT and GOPATH variables
+func init() {
+	root := runtime.GOROOT()
+	t, err := newTree(root)
+	if err != nil {
+		log.Printf("go/build: invalid GOROOT %q: %v", root, err)
+	} else {
+		t.Goroot = true
+		Path = []*Tree{t}
+	}
+
+	for _, p := range filepath.SplitList(os.Getenv("GOPATH")) {
+		if p == "" {
+			continue
+		}
+		t, err := newTree(p)
+		if err != nil {
+			log.Printf("go/build: invalid GOPATH %q: %v", p, err)
+			continue
+		}
+		Path = append(Path, t)
+		gcImportArgs = append(gcImportArgs, "-I", t.PkgDir())
+		ldImportArgs = append(ldImportArgs, "-L", t.PkgDir())
+
+		// select first GOPATH entry as default
+		if defaultTree == nil {
+			defaultTree = t
+		}
+	}
+
+	// use GOROOT if no valid GOPATH specified
+	if defaultTree == nil && len(Path) > 0 {
+		defaultTree = Path[0]
+	}
+}
diff --git a/src/pkg/go/build/pkgtest/pkgtest.go b/src/pkg/go/build/pkgtest/pkgtest.go
new file mode 100644
index 000000000..9322f5ebd
--- /dev/null
+++ b/src/pkg/go/build/pkgtest/pkgtest.go
@@ -0,0 +1,9 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package pkgtest
+
+func Foo() {}
+
+func Sqrt(x float64) float64
diff --git a/src/pkg/go/build/pkgtest/sqrt_386.s b/src/pkg/go/build/pkgtest/sqrt_386.s
new file mode 100644
index 000000000..d0a428d52
--- /dev/null
+++ b/src/pkg/go/build/pkgtest/sqrt_386.s
@@ -0,0 +1,10 @@
+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// func Sqrt(x float64) float64	
+TEXT ·Sqrt(SB),7,$0
+	FMOVD   x+0(FP),F0
+	FSQRT
+	FMOVDP  F0,r+8(FP)
+	RET
diff --git a/src/pkg/go/build/pkgtest/sqrt_amd64.s b/src/pkg/go/build/pkgtest/sqrt_amd64.s
new file mode 100644
index 000000000..f5b329e70
--- /dev/null
+++ b/src/pkg/go/build/pkgtest/sqrt_amd64.s
@@ -0,0 +1,9 @@
+// Copyright 2009 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// func Sqrt(x float64) float64
+TEXT ·Sqrt(SB),7,$0
+	SQRTSD x+0(FP), X0
+	MOVSD X0, r+8(FP)
+	RET
diff --git a/src/pkg/go/build/pkgtest/sqrt_arm.s b/src/pkg/go/build/pkgtest/sqrt_arm.s
new file mode 100644
index 000000000..befbb8a89
--- /dev/null
+++ b/src/pkg/go/build/pkgtest/sqrt_arm.s
@@ -0,0 +1,10 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// func Sqrt(x float64) float64	
+TEXT ·Sqrt(SB),7,$0
+	MOVD   x+0(FP),F0
+	SQRTD  F0,F0
+	MOVD  F0,r+8(FP)
+	RET
diff --git a/src/pkg/go/build/syslist_test.go b/src/pkg/go/build/syslist_test.go
new file mode 100644
index 000000000..eb0e5dcb6
--- /dev/null
+++ b/src/pkg/go/build/syslist_test.go
@@ -0,0 +1,62 @@
+// Copyright 2011 The Go Authors.  All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package build
+
+import (
+	"runtime"
+	"testing"
+)
+
+var (
+	thisOS    = runtime.GOOS
+	thisArch  = runtime.GOARCH
+	otherOS   = anotherOS()
+	otherArch = anotherArch()
+)
+
+func anotherOS() string {
+	if thisOS != "darwin" {
+		return "darwin"
+	}
+	return "linux"
+}
+
+func anotherArch() string {
+	if thisArch != "amd64" {
+		return "amd64"
+	}
+	return "386"
+}
+
+type GoodFileTest struct {
+	name   string
+	result bool
+}
+
+var tests = []GoodFileTest{
+	{"file.go", true},
+	{"file.c", true},
+	{"file_foo.go", true},
+	{"file_" + thisArch + ".go", true},
+	{"file_" + otherArch + ".go", false},
+	{"file_" + thisOS + ".go", true},
+	{"file_" + otherOS + ".go", false},
+	{"file_" + thisOS + "_" + thisArch + ".go", true},
+	{"file_" + otherOS + "_" + thisArch + ".go", false},
+	{"file_" + thisOS + "_" + otherArch + ".go", false},
+	{"file_" + otherOS + "_" + otherArch + ".go", false},
+	{"file_foo_" + thisArch + ".go", true},
+	{"file_foo_" + otherArch + ".go", false},
+	{"file_" + thisOS + ".c", true},
+	{"file_" + otherOS + ".c", false},
+}
+
+func TestGoodOSArch(t *testing.T) {
+	for _, test := range tests {
+		if goodOSArch(test.name) != test.result {
+			t.Fatalf("goodOSArch(%q) != %v", test.name, test.result)
+		}
+	}
+}
diff --git a/src/pkg/go/doc/Makefile b/src/pkg/go/doc/Makefile
new file mode 100644
index 000000000..a5152c793
--- /dev/null
+++ b/src/pkg/go/doc/Makefile
@@ -0,0 +1,12 @@
+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../Make.inc
+
+TARG=go/doc
+GOFILES=\
+	comment.go\
+	doc.go\
+
+include ../../../Make.pkg
diff --git a/src/pkg/go/doc/comment.go b/src/pkg/go/doc/comment.go
new file mode 100644
index 000000000..e1989226b
--- /dev/null
+++ b/src/pkg/go/doc/comment.go
@@ -0,0 +1,345 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Godoc comment extraction and comment -> HTML formatting.
+
+package doc
+
+import (
+	"go/ast"
+	"io"
+	"regexp"
+	"strings"
+	"template" // for HTMLEscape
+)
+
+func isWhitespace(ch byte) bool { return ch == ' ' || ch == '\t' || ch == '\n' || ch == '\r' }
+
+func stripTrailingWhitespace(s string) string {
+	i := len(s)
+	for i > 0 && isWhitespace(s[i-1]) {
+		i--
+	}
+	return s[0:i]
+}
+
+// CommentText returns the text of comment,
+// with the comment markers - //, /*, and */ - removed.
+func CommentText(comment *ast.CommentGroup) string {
+	if comment == nil {
+		return ""
+	}
+	comments := make([]string, len(comment.List))
+	for i, c := range comment.List {
+		comments[i] = string(c.Text)
+	}
+
+	lines := make([]string, 0, 10) // most comments are less than 10 lines
+	for _, c := range comments {
+		// Remove comment markers.
+		// The parser has given us exactly the comment text.
+		switch c[1] {
+		case '/':
+			//-style comment
+			c = c[2:]
+			// Remove leading space after //, if there is one.
+			// TODO(gri) This appears to be necessary in isolated
+			//           cases (bignum.RatFromString) - why?
+			if len(c) > 0 && c[0] == ' ' {
+				c = c[1:]
+			}
+		case '*':
+			/*-style comment */
+			c = c[2 : len(c)-2]
+		}
+
+		// Split on newlines.
+		cl := strings.Split(c, "\n")
+
+		// Walk lines, stripping trailing white space and adding to list.
+		for _, l := range cl {
+			lines = append(lines, stripTrailingWhitespace(l))
+		}
+	}
+
+	// Remove leading blank lines; convert runs of
+	// interior blank lines to a single blank line.
+	n := 0
+	for _, line := range lines {
+		if line != "" || n > 0 && lines[n-1] != "" {
+			lines[n] = line
+			n++
+		}
+	}
+	lines = lines[0:n]
+
+	// Add final "" entry to get trailing newline from Join.
+	if n > 0 && lines[n-1] != "" {
+		lines = append(lines, "")
+	}
+
+	return strings.Join(lines, "\n")
+}
+
+// Split bytes into lines.
+func split(text []byte) [][]byte {
+	// count lines
+	n := 0
+	last := 0
+	for i, c := range text {
+		if c == '\n' {
+			last = i + 1
+			n++
+		}
+	}
+	if last < len(text) {
+		n++
+	}
+
+	// split
+	out := make([][]byte, n)
+	last = 0
+	n = 0
+	for i, c := range text {
+		if c == '\n' {
+			out[n] = text[last : i+1]
+			last = i + 1
+			n++
+		}
+	}
+	if last < len(text) {
+		out[n] = text[last:]
+	}
+
+	return out
+}
+
+var (
+	ldquo = []byte("&ldquo;")
+	rdquo = []byte("&rdquo;")
+)
+
+// Escape comment text for HTML. If nice is set,
+// also turn `` into &ldquo; and '' into &rdquo;.
+func commentEscape(w io.Writer, s []byte, nice bool) {
+	last := 0
+	if nice {
+		for i := 0; i < len(s)-1; i++ {
+			ch := s[i]
+			if ch == s[i+1] && (ch == '`' || ch == '\'') {
+				template.HTMLEscape(w, s[last:i])
+				last = i + 2
+				switch ch {
+				case '`':
+					w.Write(ldquo)
+				case '\'':
+					w.Write(rdquo)
+				}
+				i++ // loop will add one more
+			}
+		}
+	}
+	template.HTMLEscape(w, s[last:])
+}
+
+const (
+	// Regexp for Go identifiers
+	identRx = `[a-zA-Z_][a-zA-Z_0-9]*` // TODO(gri) ASCII only for now - fix this
+
+	// Regexp for URLs
+	protocol = `(https?|ftp|file|gopher|mailto|news|nntp|telnet|wais|prospero):`
+	hostPart = `[a-zA-Z0-9_@\-]+`
+	filePart = `[a-zA-Z0-9_?%#~&/\-+=]+`
+	urlRx    = protocol + `//` + // http://
+		hostPart + `([.:]` + hostPart + `)*/?` + // //www.google.com:8080/
+		filePart + `([:.,]` + filePart + `)*`
+)
+
+var matchRx = regexp.MustCompile(`(` + identRx + `)|(` + urlRx + `)`)
+
+var (
+	html_a      = []byte(`<a href="`)
+	html_aq     = []byte(`">`)
+	html_enda   = []byte("</a>")
+	html_i      = []byte("<i>")
+	html_endi   = []byte("</i>")
+	html_p      = []byte("<p>\n")
+	html_endp   = []byte("</p>\n")
+	html_pre    = []byte("<pre>")
+	html_endpre = []byte("</pre>\n")
+)
+
+// Emphasize and escape a line of text for HTML. URLs are converted into links;
+// if the URL also appears in the words map, the link is taken from the map (if
+// the corresponding map value is the empty string, the URL is not converted
+// into a link). Go identifiers that appear in the words map are italicized; if
+// the corresponding map value is not the empty string, it is considered a URL
+// and the word is converted into a link. If nice is set, the remaining text's
+// appearance is improved where it makes sense (e.g., `` is turned into &ldquo;
+// and '' into &rdquo;).
+func emphasize(w io.Writer, line []byte, words map[string]string, nice bool) {
+	for {
+		m := matchRx.FindSubmatchIndex(line)
+		if m == nil {
+			break
+		}
+		// m >= 6 (two parenthesized sub-regexps in matchRx, 1st one is identRx)
+
+		// write text before match
+		commentEscape(w, line[0:m[0]], nice)
+
+		// analyze match
+		match := line[m[0]:m[1]]
+		url := ""
+		italics := false
+		if words != nil {
+			url, italics = words[string(match)]
+		}
+		if m[2] < 0 {
+			// didn't match against first parenthesized sub-regexp; must be match against urlRx
+			if !italics {
+				// no alternative URL in words list, use match instead
+				url = string(match)
+			}
+			italics = false // don't italicize URLs
+		}
+
+		// write match
+		if len(url) > 0 {
+			w.Write(html_a)
+			template.HTMLEscape(w, []byte(url))
+			w.Write(html_aq)
+		}
+		if italics {
+			w.Write(html_i)
+		}
+		commentEscape(w, match, nice)
+		if italics {
+			w.Write(html_endi)
+		}
+		if len(url) > 0 {
+			w.Write(html_enda)
+		}
+
+		// advance
+		line = line[m[1]:]
+	}
+	commentEscape(w, line, nice)
+}
+
+func indentLen(s []byte) int {
+	i := 0
+	for i < len(s) && (s[i] == ' ' || s[i] == '\t') {
+		i++
+	}
+	return i
+}
+
+func isBlank(s []byte) bool { return len(s) == 0 || (len(s) == 1 && s[0] == '\n') }
+
+func commonPrefix(a, b []byte) []byte {
+	i := 0
+	for i < len(a) && i < len(b) && a[i] == b[i] {
+		i++
+	}
+	return a[0:i]
+}
+
+func unindent(block [][]byte) {
+	if len(block) == 0 {
+		return
+	}
+
+	// compute maximum common white prefix
+	prefix := block[0][0:indentLen(block[0])]
+	for _, line := range block {
+		if !isBlank(line) {
+			prefix = commonPrefix(prefix, line[0:indentLen(line)])
+		}
+	}
+	n := len(prefix)
+
+	// remove
+	for i, line := range block {
+		if !isBlank(line) {
+			block[i] = line[n:]
+		}
+	}
+}
+
+// Convert comment text to formatted HTML.
+// The comment was prepared by DocReader,
+// so it is known not to have leading, trailing blank lines
+// nor to have trailing spaces at the end of lines.
+// The comment markers have already been removed.
+//
+// Turn each run of multiple \n into </p><p>.
+// Turn each run of indented lines into a <pre> block without indent.
+//
+// URLs in the comment text are converted into links; if the URL also appears
+// in the words map, the link is taken from the map (if the corresponding map
+// value is the empty string, the URL is not converted into a link).
+//
+// Go identifiers that appear in the words map are italicized; if the corresponding
+// map value is not the empty string, it is considered a URL and the word is converted
+// into a link.
+func ToHTML(w io.Writer, s []byte, words map[string]string) {
+	inpara := false
+
+	close := func() {
+		if inpara {
+			w.Write(html_endp)
+			inpara = false
+		}
+	}
+	open := func() {
+		if !inpara {
+			w.Write(html_p)
+			inpara = true
+		}
+	}
+
+	lines := split(s)
+	unindent(lines)
+	for i := 0; i < len(lines); {
+		line := lines[i]
+		if isBlank(line) {
+			// close paragraph
+			close()
+			i++
+			continue
+		}
+		if indentLen(line) > 0 {
+			// close paragraph
+			close()
+
+			// count indented or blank lines
+			j := i + 1
+			for j < len(lines) && (isBlank(lines[j]) || indentLen(lines[j]) > 0) {
+				j++
+			}
+			// but not trailing blank lines
+			for j > i && isBlank(lines[j-1]) {
+				j--
+			}
+			block := lines[i:j]
+			i = j
+
+			unindent(block)
+
+			// put those lines in a pre block
+			w.Write(html_pre)
+			for _, line := range block {
+				emphasize(w, line, nil, false) // no nice text formatting
+			}
+			w.Write(html_endpre)
+			continue
+		}
+		// open paragraph
+		open()
+		emphasize(w, lines[i], words, true) // nice text formatting
+		i++
+	}
+	close()
+}
diff --git a/src/pkg/go/doc/doc.go b/src/pkg/go/doc/doc.go
new file mode 100644
index 000000000..c7fed9784
--- /dev/null
+++ b/src/pkg/go/doc/doc.go
@@ -0,0 +1,641 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package doc extracts source code documentation from a Go AST.
+package doc
+
+import (
+	"go/ast"
+	"go/token"
+	"regexp"
+	"sort"
+)
+
+// ----------------------------------------------------------------------------
+
+type typeDoc struct {
+	// len(decl.Specs) == 1, and the element type is *ast.TypeSpec
+	// if the type declaration hasn't been seen yet, decl is nil
+	decl *ast.GenDecl
+	// values, factory functions, and methods associated with the type
+	values    []*ast.GenDecl // consts and vars
+	factories map[string]*ast.FuncDecl
+	methods   map[string]*ast.FuncDecl
+}
+
+// docReader accumulates documentation for a single package.
+// It modifies the AST: Comments (declaration documentation)
+// that have been collected by the DocReader are set to nil
+// in the respective AST nodes so that they are not printed
+// twice (once when printing the documentation and once when
+// printing the corresponding AST node).
+//
+type docReader struct {
+	doc     *ast.CommentGroup // package documentation, if any
+	pkgName string
+	values  []*ast.GenDecl // consts and vars
+	types   map[string]*typeDoc
+	funcs   map[string]*ast.FuncDecl
+	bugs    []*ast.CommentGroup
+}
+
+func (doc *docReader) init(pkgName string) {
+	doc.pkgName = pkgName
+	doc.types = make(map[string]*typeDoc)
+	doc.funcs = make(map[string]*ast.FuncDecl)
+}
+
+func (doc *docReader) addDoc(comments *ast.CommentGroup) {
+	if doc.doc == nil {
+		// common case: just one package comment
+		doc.doc = comments
+		return
+	}
+
+	// More than one package comment: Usually there will be only
+	// one file with a package comment, but it's better to collect
+	// all comments than drop them on the floor.
+	// (This code isn't particularly clever - no amortized doubling is
+	// used - but this situation occurs rarely and is not time-critical.)
+	n1 := len(doc.doc.List)
+	n2 := len(comments.List)
+	list := make([]*ast.Comment, n1+1+n2) // + 1 for separator line
+	copy(list, doc.doc.List)
+	list[n1] = &ast.Comment{token.NoPos, "//"} // separator line
+	copy(list[n1+1:], comments.List)
+	doc.doc = &ast.CommentGroup{list}
+}
+
+func (doc *docReader) addType(decl *ast.GenDecl) {
+	spec := decl.Specs[0].(*ast.TypeSpec)
+	typ := doc.lookupTypeDoc(spec.Name.Name)
+	// typ should always be != nil since declared types
+	// are always named - be conservative and check
+	if typ != nil {
+		// a type should be added at most once, so typ.decl
+		// should be nil - if it isn't, simply overwrite it
+		typ.decl = decl
+	}
+}
+
+func (doc *docReader) lookupTypeDoc(name string) *typeDoc {
+	if name == "" {
+		return nil // no type docs for anonymous types
+	}
+	if tdoc, found := doc.types[name]; found {
+		return tdoc
+	}
+	// type wasn't found - add one without declaration
+	tdoc := &typeDoc{nil, nil, make(map[string]*ast.FuncDecl), make(map[string]*ast.FuncDecl)}
+	doc.types[name] = tdoc
+	return tdoc
+}
+
+func baseTypeName(typ ast.Expr) string {
+	switch t := typ.(type) {
+	case *ast.Ident:
+		// if the type is not exported, the effect to
+		// a client is as if there were no type name
+		if t.IsExported() {
+			return t.Name
+		}
+	case *ast.StarExpr:
+		return baseTypeName(t.X)
+	}
+	return ""
+}
+
+func (doc *docReader) addValue(decl *ast.GenDecl) {
+	// determine if decl should be associated with a type
+	// Heuristic: For each typed entry, determine the type name, if any.
+	//            If there is exactly one type name that is sufficiently
+	//            frequent, associate the decl with the respective type.
+	domName := ""
+	domFreq := 0
+	prev := ""
+	for _, s := range decl.Specs {
+		if v, ok := s.(*ast.ValueSpec); ok {
+			name := ""
+			switch {
+			case v.Type != nil:
+				// a type is present; determine its name
+				name = baseTypeName(v.Type)
+			case decl.Tok == token.CONST:
+				// no type is present but we have a constant declaration;
+				// use the previous type name (w/o more type information
+				// we cannot handle the case of unnamed variables with
+				// initializer expressions except for some trivial cases)
+				name = prev
+			}
+			if name != "" {
+				// entry has a named type
+				if domName != "" && domName != name {
+					// more than one type name - do not associate
+					// with any type
+					domName = ""
+					break
+				}
+				domName = name
+				domFreq++
+			}
+			prev = name
+		}
+	}
+
+	// determine values list
+	const threshold = 0.75
+	values := &doc.values
+	if domName != "" && domFreq >= int(float64(len(decl.Specs))*threshold) {
+		// typed entries are sufficiently frequent
+		typ := doc.lookupTypeDoc(domName)
+		if typ != nil {
+			values = &typ.values // associate with that type
+		}
+	}
+
+	*values = append(*values, decl)
+}
+
+// Helper function to set the table entry for function f. Makes sure that
+// at least one f with associated documentation is stored in table, if there
+// are multiple f's with the same name.
+func setFunc(table map[string]*ast.FuncDecl, f *ast.FuncDecl) {
+	name := f.Name.Name
+	if g, exists := table[name]; exists && g.Doc != nil {
+		// a function with the same name has already been registered;
+		// since it has documentation, assume f is simply another
+		// implementation and ignore it
+		// TODO(gri) consider collecting all functions, or at least
+		//           all comments
+		return
+	}
+	// function doesn't exist or has no documentation; use f
+	table[name] = f
+}
+
+func (doc *docReader) addFunc(fun *ast.FuncDecl) {
+	name := fun.Name.Name
+
+	// determine if it should be associated with a type
+	if fun.Recv != nil {
+		// method
+		typ := doc.lookupTypeDoc(baseTypeName(fun.Recv.List[0].Type))
+		if typ != nil {
+			// exported receiver type
+			setFunc(typ.methods, fun)
+		}
+		// otherwise don't show the method
+		// TODO(gri): There may be exported methods of non-exported types
+		// that can be called because of exported values (consts, vars, or
+		// function results) of that type. Could determine if that is the
+		// case and then show those methods in an appropriate section.
+		return
+	}
+
+	// perhaps a factory function
+	// determine result type, if any
+	if fun.Type.Results.NumFields() >= 1 {
+		res := fun.Type.Results.List[0]
+		if len(res.Names) <= 1 {
+			// exactly one (named or anonymous) result associated
+			// with the first type in result signature (there may
+			// be more than one result)
+			tname := baseTypeName(res.Type)
+			typ := doc.lookupTypeDoc(tname)
+			if typ != nil {
+				// named and exported result type
+
+				// Work-around for failure of heuristic: In package os
+				// too many functions are considered factory functions
+				// for the Error type. Eliminate manually for now as
+				// this appears to be the only important case in the
+				// current library where the heuristic fails.
+				if doc.pkgName == "os" && tname == "Error" &&
+					name != "NewError" && name != "NewSyscallError" {
+					// not a factory function for os.Error
+					setFunc(doc.funcs, fun) // treat as ordinary function
+					return
+				}
+
+				setFunc(typ.factories, fun)
+				return
+			}
+		}
+	}
+
+	// ordinary function
+	setFunc(doc.funcs, fun)
+}
+
+func (doc *docReader) addDecl(decl ast.Decl) {
+	switch d := decl.(type) {
+	case *ast.GenDecl:
+		if len(d.Specs) > 0 {
+			switch d.Tok {
+			case token.CONST, token.VAR:
+				// constants and variables are always handled as a group
+				doc.addValue(d)
+			case token.TYPE:
+				// types are handled individually
+				for _, spec := range d.Specs {
+					// make a (fake) GenDecl node for this TypeSpec
+					// (we need to do this here - as opposed to just
+					// for printing - so we don't lose the GenDecl
+					// documentation)
+					//
+					// TODO(gri): Consider just collecting the TypeSpec
+					// node (and copy in the GenDecl.doc if there is no
+					// doc in the TypeSpec - this is currently done in
+					// makeTypeDocs below). Simpler data structures, but
+					// would lose GenDecl documentation if the TypeSpec
+					// has documentation as well.
+					doc.addType(&ast.GenDecl{d.Doc, d.Pos(), token.TYPE, token.NoPos, []ast.Spec{spec}, token.NoPos})
+					// A new GenDecl node is created, no need to nil out d.Doc.
+				}
+			}
+		}
+	case *ast.FuncDecl:
+		doc.addFunc(d)
+	}
+}
+
+func copyCommentList(list []*ast.Comment) []*ast.Comment {
+	return append([]*ast.Comment(nil), list...)
+}
+
+var (
+	bug_markers = regexp.MustCompile("^/[/*][ \t]*BUG\\(.*\\):[ \t]*") // BUG(uid):
+	bug_content = regexp.MustCompile("[^ \n\r\t]+")                    // at least one non-whitespace char
+)
+
+// addFile adds the AST for a source file to the docReader.
+// Adding the same AST multiple times is a no-op.
+//
+func (doc *docReader) addFile(src *ast.File) {
+	// add package documentation
+	if src.Doc != nil {
+		doc.addDoc(src.Doc)
+		src.Doc = nil // doc consumed - remove from ast.File node
+	}
+
+	// add all declarations
+	for _, decl := range src.Decls {
+		doc.addDecl(decl)
+	}
+
+	// collect BUG(...) comments
+	for _, c := range src.Comments {
+		text := c.List[0].Text
+		if m := bug_markers.FindStringIndex(text); m != nil {
+			// found a BUG comment; maybe empty
+			if btxt := text[m[1]:]; bug_content.MatchString(btxt) {
+				// non-empty BUG comment; collect comment without BUG prefix
+				list := copyCommentList(c.List)
+				list[0].Text = text[m[1]:]
+				doc.bugs = append(doc.bugs, &ast.CommentGroup{list})
+			}
+		}
+	}
+	src.Comments = nil // consumed unassociated comments - remove from ast.File node
+}
+
+func NewFileDoc(file *ast.File) *PackageDoc {
+	var r docReader
+	r.init(file.Name.Name)
+	r.addFile(file)
+	return r.newDoc("", nil)
+}
+
+func NewPackageDoc(pkg *ast.Package, importpath string) *PackageDoc {
+	var r docReader
+	r.init(pkg.Name)
+	filenames := make([]string, len(pkg.Files))
+	i := 0
+	for filename, f := range pkg.Files {
+		r.addFile(f)
+		filenames[i] = filename
+		i++
+	}
+	return r.newDoc(importpath, filenames)
+}
+
+// ----------------------------------------------------------------------------
+// Conversion to external representation
+
+// ValueDoc is the documentation for a group of declared
+// values, either vars or consts.
+//
+type ValueDoc struct {
+	Doc   string
+	Decl  *ast.GenDecl
+	order int
+}
+
+type sortValueDoc []*ValueDoc
+
+func (p sortValueDoc) Len() int      { return len(p) }
+func (p sortValueDoc) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
+
+func declName(d *ast.GenDecl) string {
+	if len(d.Specs) != 1 {
+		return ""
+	}
+
+	switch v := d.Specs[0].(type) {
+	case *ast.ValueSpec:
+		return v.Names[0].Name
+	case *ast.TypeSpec:
+		return v.Name.Name
+	}
+
+	return ""
+}
+
+func (p sortValueDoc) Less(i, j int) bool {
+	// sort by name
+	// pull blocks (name = "") up to top
+	// in original order
+	if ni, nj := declName(p[i].Decl), declName(p[j].Decl); ni != nj {
+		return ni < nj
+	}
+	return p[i].order < p[j].order
+}
+
+func makeValueDocs(list []*ast.GenDecl, tok token.Token) []*ValueDoc {
+	d := make([]*ValueDoc, len(list)) // big enough in any case
+	n := 0
+	for i, decl := range list {
+		if decl.Tok == tok {
+			d[n] = &ValueDoc{CommentText(decl.Doc), decl, i}
+			n++
+			decl.Doc = nil // doc consumed - removed from AST
+		}
+	}
+	d = d[0:n]
+	sort.Sort(sortValueDoc(d))
+	return d
+}
+
+// FuncDoc is the documentation for a func declaration,
+// either a top-level function or a method function.
+//
+type FuncDoc struct {
+	Doc  string
+	Recv ast.Expr // TODO(rsc): Would like string here
+	Name string
+	Decl *ast.FuncDecl
+}
+
+type sortFuncDoc []*FuncDoc
+
+func (p sortFuncDoc) Len() int           { return len(p) }
+func (p sortFuncDoc) Swap(i, j int)      { p[i], p[j] = p[j], p[i] }
+func (p sortFuncDoc) Less(i, j int) bool { return p[i].Name < p[j].Name }
+
+func makeFuncDocs(m map[string]*ast.FuncDecl) []*FuncDoc {
+	d := make([]*FuncDoc, len(m))
+	i := 0
+	for _, f := range m {
+		doc := new(FuncDoc)
+		doc.Doc = CommentText(f.Doc)
+		f.Doc = nil // doc consumed - remove from ast.FuncDecl node
+		if f.Recv != nil {
+			doc.Recv = f.Recv.List[0].Type
+		}
+		doc.Name = f.Name.Name
+		doc.Decl = f
+		d[i] = doc
+		i++
+	}
+	sort.Sort(sortFuncDoc(d))
+	return d
+}
+
+// TypeDoc is the documentation for a declared type.
+// Consts and Vars are sorted lists of constants and variables of (mostly) that type.
+// Factories is a sorted list of factory functions that return that type.
+// Methods is a sorted list of method functions on that type.
+type TypeDoc struct {
+	Doc       string
+	Type      *ast.TypeSpec
+	Consts    []*ValueDoc
+	Vars      []*ValueDoc
+	Factories []*FuncDoc
+	Methods   []*FuncDoc
+	Decl      *ast.GenDecl
+	order     int
+}
+
+type sortTypeDoc []*TypeDoc
+
+func (p sortTypeDoc) Len() int      { return len(p) }
+func (p sortTypeDoc) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
+func (p sortTypeDoc) Less(i, j int) bool {
+	// sort by name
+	// pull blocks (name = "") up to top
+	// in original order
+	if ni, nj := p[i].Type.Name.Name, p[j].Type.Name.Name; ni != nj {
+		return ni < nj
+	}
+	return p[i].order < p[j].order
+}
+
+// NOTE(rsc): This would appear not to be correct for type ( )
+// blocks, but the doc extractor above has split them into
+// individual declarations.
+func (doc *docReader) makeTypeDocs(m map[string]*typeDoc) []*TypeDoc {
+	d := make([]*TypeDoc, len(m))
+	i := 0
+	for _, old := range m {
+		// all typeDocs should have a declaration associated with
+		// them after processing an entire package - be conservative
+		// and check
+		if decl := old.decl; decl != nil {
+			typespec := decl.Specs[0].(*ast.TypeSpec)
+			t := new(TypeDoc)
+			doc := typespec.Doc
+			typespec.Doc = nil // doc consumed - remove from ast.TypeSpec node
+			if doc == nil {
+				// no doc associated with the spec, use the declaration doc, if any
+				doc = decl.Doc
+			}
+			decl.Doc = nil // doc consumed - remove from ast.Decl node
+			t.Doc = CommentText(doc)
+			t.Type = typespec
+			t.Consts = makeValueDocs(old.values, token.CONST)
+			t.Vars = makeValueDocs(old.values, token.VAR)
+			t.Factories = makeFuncDocs(old.factories)
+			t.Methods = makeFuncDocs(old.methods)
+			t.Decl = old.decl
+			t.order = i
+			d[i] = t
+			i++
+		} else {
+			// no corresponding type declaration found - move any associated
+			// values, factory functions, and methods back to the top-level
+			// so that they are not lost (this should only happen if a package
+			// file containing the explicit type declaration is missing or if
+			// an unqualified type name was used after a "." import)
+			// 1) move values
+			doc.values = append(doc.values, old.values...)
+			// 2) move factory functions
+			for name, f := range old.factories {
+				doc.funcs[name] = f
+			}
+			// 3) move methods
+			for name, f := range old.methods {
+				// don't overwrite functions with the same name
+				if _, found := doc.funcs[name]; !found {
+					doc.funcs[name] = f
+				}
+			}
+		}
+	}
+	d = d[0:i] // some types may have been ignored
+	sort.Sort(sortTypeDoc(d))
+	return d
+}
+
+func makeBugDocs(list []*ast.CommentGroup) []string {
+	d := make([]string, len(list))
+	for i, g := range list {
+		d[i] = CommentText(g)
+	}
+	return d
+}
+
+// PackageDoc is the documentation for an entire package.
+//
+type PackageDoc struct {
+	PackageName string
+	ImportPath  string
+	Filenames   []string
+	Doc         string
+	Consts      []*ValueDoc
+	Types       []*TypeDoc
+	Vars        []*ValueDoc
+	Funcs       []*FuncDoc
+	Bugs        []string
+}
+
+// newDoc returns the accumulated documentation for the package.
+//
+func (doc *docReader) newDoc(importpath string, filenames []string) *PackageDoc {
+	p := new(PackageDoc)
+	p.PackageName = doc.pkgName
+	p.ImportPath = importpath
+	sort.Strings(filenames)
+	p.Filenames = filenames
+	p.Doc = CommentText(doc.doc)
+	// makeTypeDocs may extend the list of doc.values and
+	// doc.funcs and thus must be called before any other
+	// function consuming those lists
+	p.Types = doc.makeTypeDocs(doc.types)
+	p.Consts = makeValueDocs(doc.values, token.CONST)
+	p.Vars = makeValueDocs(doc.values, token.VAR)
+	p.Funcs = makeFuncDocs(doc.funcs)
+	p.Bugs = makeBugDocs(doc.bugs)
+	return p
+}
+
+// ----------------------------------------------------------------------------
+// Filtering by name
+
+type Filter func(string) bool
+
+func matchFields(fields *ast.FieldList, f Filter) bool {
+	if fields != nil {
+		for _, field := range fields.List {
+			for _, name := range field.Names {
+				if f(name.Name) {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+func matchDecl(d *ast.GenDecl, f Filter) bool {
+	for _, d := range d.Specs {
+		switch v := d.(type) {
+		case *ast.ValueSpec:
+			for _, name := range v.Names {
+				if f(name.Name) {
+					return true
+				}
+			}
+		case *ast.TypeSpec:
+			if f(v.Name.Name) {
+				return true
+			}
+			switch t := v.Type.(type) {
+			case *ast.StructType:
+				if matchFields(t.Fields, f) {
+					return true
+				}
+			case *ast.InterfaceType:
+				if matchFields(t.Methods, f) {
+					return true
+				}
+			}
+		}
+	}
+	return false
+}
+
+func filterValueDocs(a []*ValueDoc, f Filter) []*ValueDoc {
+	w := 0
+	for _, vd := range a {
+		if matchDecl(vd.Decl, f) {
+			a[w] = vd
+			w++
+		}
+	}
+	return a[0:w]
+}
+
+func filterFuncDocs(a []*FuncDoc, f Filter) []*FuncDoc {
+	w := 0
+	for _, fd := range a {
+		if f(fd.Name) {
+			a[w] = fd
+			w++
+		}
+	}
+	return a[0:w]
+}
+
+func filterTypeDocs(a []*TypeDoc, f Filter) []*TypeDoc {
+	w := 0
+	for _, td := range a {
+		n := 0 // number of matches
+		if matchDecl(td.Decl, f) {
+			n = 1
+		} else {
+			// type name doesn't match, but we may have matching consts, vars, factories or methods
+			td.Consts = filterValueDocs(td.Consts, f)
+			td.Vars = filterValueDocs(td.Vars, f)
+			td.Factories = filterFuncDocs(td.Factories, f)
+			td.Methods = filterFuncDocs(td.Methods, f)
+			n += len(td.Consts) + len(td.Vars) + len(td.Factories) + len(td.Methods)
+		}
+		if n > 0 {
+			a[w] = td
+			w++
+		}
+	}
+	return a[0:w]
+}
+
+// Filter eliminates documentation for names that don't pass through the filter f.
+// TODO: Recognize "Type.Method" as a name.
+//
+func (p *PackageDoc) Filter(f Filter) {
+	p.Consts = filterValueDocs(p.Consts, f)
+	p.Vars = filterValueDocs(p.Vars, f)
+	p.Types = filterTypeDocs(p.Types, f)
+	p.Funcs = filterFuncDocs(p.Funcs, f)
+	p.Doc = "" // don't show top-level package doc
+}
diff --git a/src/pkg/go/parser/Makefile b/src/pkg/go/parser/Makefile
new file mode 100644
index 000000000..d301f41eb
--- /dev/null
+++ b/src/pkg/go/parser/Makefile
@@ -0,0 +1,12 @@
+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../Make.inc
+
+TARG=go/parser
+GOFILES=\
+	interface.go\
+	parser.go\
+
+include ../../../Make.pkg
diff --git a/src/pkg/go/parser/interface.go b/src/pkg/go/parser/interface.go
new file mode 100644
index 000000000..4f980fc65
--- /dev/null
+++ b/src/pkg/go/parser/interface.go
@@ -0,0 +1,214 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file contains the exported entry points for invoking the parser.
+
+package parser
+
+import (
+	"bytes"
+	"go/ast"
+	"go/scanner"
+	"go/token"
+	"io"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+)
+
+// If src != nil, readSource converts src to a []byte if possible;
+// otherwise it returns an error. If src == nil, readSource returns
+// the result of reading the file specified by filename.
+//
+func readSource(filename string, src interface{}) ([]byte, os.Error) {
+	if src != nil {
+		switch s := src.(type) {
+		case string:
+			return []byte(s), nil
+		case []byte:
+			return s, nil
+		case *bytes.Buffer:
+			// is io.Reader, but src is already available in []byte form
+			if s != nil {
+				return s.Bytes(), nil
+			}
+		case io.Reader:
+			var buf bytes.Buffer
+			_, err := io.Copy(&buf, s)
+			if err != nil {
+				return nil, err
+			}
+			return buf.Bytes(), nil
+		default:
+			return nil, os.NewError("invalid source")
+		}
+	}
+
+	return ioutil.ReadFile(filename)
+}
+
+func (p *parser) errors() os.Error {
+	mode := scanner.Sorted
+	if p.mode&SpuriousErrors == 0 {
+		mode = scanner.NoMultiples
+	}
+	return p.GetError(mode)
+}
+
+// ParseExpr parses a Go expression and returns the corresponding
+// AST node. The fset, filename, and src arguments have the same interpretation
+// as for ParseFile. If there is an error, the result expression
+// may be nil or contain a partial AST.
+//
+func ParseExpr(fset *token.FileSet, filename string, src interface{}) (ast.Expr, os.Error) {
+	data, err := readSource(filename, src)
+	if err != nil {
+		return nil, err
+	}
+
+	var p parser
+	p.init(fset, filename, data, 0)
+	x := p.parseRhs()
+	if p.tok == token.SEMICOLON {
+		p.next() // consume automatically inserted semicolon, if any
+	}
+	p.expect(token.EOF)
+
+	return x, p.errors()
+}
+
+// ParseStmtList parses a list of Go statements and returns the list
+// of corresponding AST nodes. The fset, filename, and src arguments have the same
+// interpretation as for ParseFile. If there is an error, the node
+// list may be nil or contain partial ASTs.
+//
+func ParseStmtList(fset *token.FileSet, filename string, src interface{}) ([]ast.Stmt, os.Error) {
+	data, err := readSource(filename, src)
+	if err != nil {
+		return nil, err
+	}
+
+	var p parser
+	p.init(fset, filename, data, 0)
+	list := p.parseStmtList()
+	p.expect(token.EOF)
+
+	return list, p.errors()
+}
+
+// ParseDeclList parses a list of Go declarations and returns the list
+// of corresponding AST nodes. The fset, filename, and src arguments have the same
+// interpretation as for ParseFile. If there is an error, the node
+// list may be nil or contain partial ASTs.
+//
+func ParseDeclList(fset *token.FileSet, filename string, src interface{}) ([]ast.Decl, os.Error) {
+	data, err := readSource(filename, src)
+	if err != nil {
+		return nil, err
+	}
+
+	var p parser
+	p.init(fset, filename, data, 0)
+	list := p.parseDeclList()
+	p.expect(token.EOF)
+
+	return list, p.errors()
+}
+
+// ParseFile parses the source code of a single Go source file and returns
+// the corresponding ast.File node. The source code may be provided via
+// the filename of the source file, or via the src parameter.
+//
+// If src != nil, ParseFile parses the source from src and the filename is
+// only used when recording position information. The type of the argument
+// for the src parameter must be string, []byte, or io.Reader.
+//
+// If src == nil, ParseFile parses the file specified by filename.
+//
+// The mode parameter controls the amount of source text parsed and other
+// optional parser functionality. Position information is recorded in the
+// file set fset.
+//
+// If the source couldn't be read, the returned AST is nil and the error
+// indicates the specific failure. If the source was read but syntax
+// errors were found, the result is a partial AST (with ast.BadX nodes
+// representing the fragments of erroneous source code). Multiple errors
+// are returned via a scanner.ErrorList which is sorted by file position.
+//
+func ParseFile(fset *token.FileSet, filename string, src interface{}, mode uint) (*ast.File, os.Error) {
+	data, err := readSource(filename, src)
+	if err != nil {
+		return nil, err
+	}
+
+	var p parser
+	p.init(fset, filename, data, mode)
+	file := p.parseFile() // parseFile reads to EOF
+
+	return file, p.errors()
+}
+
+// ParseFiles calls ParseFile for each file in the filenames list and returns
+// a map of package name -> package AST with all the packages found. The mode
+// bits are passed to ParseFile unchanged. Position information is recorded
+// in the file set fset.
+//
+// Files with parse errors are ignored. In this case the map of packages may
+// be incomplete (missing packages and/or incomplete packages) and the first
+// error encountered is returned.
+//
+func ParseFiles(fset *token.FileSet, filenames []string, mode uint) (pkgs map[string]*ast.Package, first os.Error) {
+	pkgs = make(map[string]*ast.Package)
+	for _, filename := range filenames {
+		if src, err := ParseFile(fset, filename, nil, mode); err == nil {
+			name := src.Name.Name
+			pkg, found := pkgs[name]
+			if !found {
+				// TODO(gri) Use NewPackage here; reconsider ParseFiles API.
+				pkg = &ast.Package{name, nil, nil, make(map[string]*ast.File)}
+				pkgs[name] = pkg
+			}
+			pkg.Files[filename] = src
+		} else if first == nil {
+			first = err
+		}
+	}
+	return
+}
+
+// ParseDir calls ParseFile for the files in the directory specified by path and
+// returns a map of package name -> package AST with all the packages found. If
+// filter != nil, only the files with os.FileInfo entries passing through the filter
+// are considered. The mode bits are passed to ParseFile unchanged. Position
+// information is recorded in the file set fset.
+//
+// If the directory couldn't be read, a nil map and the respective error are
+// returned. If a parse error occurred, a non-nil but incomplete map and the
+// error are returned.
+//
+func ParseDir(fset *token.FileSet, path string, filter func(*os.FileInfo) bool, mode uint) (map[string]*ast.Package, os.Error) {
+	fd, err := os.Open(path)
+	if err != nil {
+		return nil, err
+	}
+	defer fd.Close()
+
+	list, err := fd.Readdir(-1)
+	if err != nil {
+		return nil, err
+	}
+
+	filenames := make([]string, len(list))
+	n := 0
+	for i := 0; i < len(list); i++ {
+		d := &list[i]
+		if filter == nil || filter(d) {
+			filenames[n] = filepath.Join(path, d.Name)
+			n++
+		}
+	}
+	filenames = filenames[0:n]
+
+	return ParseFiles(fset, filenames, mode)
+}
diff --git a/src/pkg/go/parser/parser.go b/src/pkg/go/parser/parser.go
new file mode 100644
index 000000000..9c14d1667
--- /dev/null
+++ b/src/pkg/go/parser/parser.go
@@ -0,0 +1,2161 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package parser implements a parser for Go source files. Input may be
+// provided in a variety of forms (see the various Parse* functions); the
+// output is an abstract syntax tree (AST) representing the Go source. The
+// parser is invoked through one of the Parse* functions.
+//
+package parser
+
+import (
+	"fmt"
+	"go/ast"
+	"go/scanner"
+	"go/token"
+)
+
+// The mode parameter to the Parse* functions is a set of flags (or 0).
+// They control the amount of source code parsed and other optional
+// parser functionality.
+//
+const (
+	PackageClauseOnly uint = 1 << iota // parsing stops after package clause
+	ImportsOnly                        // parsing stops after import declarations
+	ParseComments                      // parse comments and add them to AST
+	Trace                              // print a trace of parsed productions
+	DeclarationErrors                  // report declaration errors
+	SpuriousErrors                     // report all (not just the first) errors per line
+)
+
+// The parser structure holds the parser's internal state.
+type parser struct {
+	file *token.File
+	scanner.ErrorVector
+	scanner scanner.Scanner
+
+	// Tracing/debugging
+	mode   uint // parsing mode
+	trace  bool // == (mode & Trace != 0)
+	indent uint // indentation used for tracing output
+
+	// Comments
+	comments    []*ast.CommentGroup
+	leadComment *ast.CommentGroup // last lead comment
+	lineComment *ast.CommentGroup // last line comment
+
+	// Next token
+	pos token.Pos   // token position
+	tok token.Token // one token look-ahead
+	lit string      // token literal
+
+	// Non-syntactic parser control
+	exprLev int // < 0: in control clause, >= 0: in expression
+
+	// Ordinary identifier scopes
+	pkgScope   *ast.Scope        // pkgScope.Outer == nil
+	topScope   *ast.Scope        // top-most scope; may be pkgScope
+	unresolved []*ast.Ident      // unresolved identifiers
+	imports    []*ast.ImportSpec // list of imports
+
+	// Label scope
+	// (maintained by open/close LabelScope)
+	labelScope  *ast.Scope     // label scope for current function
+	targetStack [][]*ast.Ident // stack of unresolved labels
+}
+
+// scannerMode returns the scanner mode bits given the parser's mode bits.
+func scannerMode(mode uint) uint {
+	var m uint = scanner.InsertSemis
+	if mode&ParseComments != 0 {
+		m |= scanner.ScanComments
+	}
+	return m
+}
+
+func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode uint) {
+	p.file = fset.AddFile(filename, fset.Base(), len(src))
+	p.scanner.Init(p.file, src, p, scannerMode(mode))
+
+	p.mode = mode
+	p.trace = mode&Trace != 0 // for convenience (p.trace is used frequently)
+
+	p.next()
+
+	// set up the pkgScope here (as opposed to in parseFile) because
+	// there are other parser entry points (ParseExpr, etc.)
+	p.openScope()
+	p.pkgScope = p.topScope
+
+	// for the same reason, set up a label scope
+	p.openLabelScope()
+}
+
+// ----------------------------------------------------------------------------
+// Scoping support
+
+func (p *parser) openScope() {
+	p.topScope = ast.NewScope(p.topScope)
+}
+
+func (p *parser) closeScope() {
+	p.topScope = p.topScope.Outer
+}
+
+func (p *parser) openLabelScope() {
+	p.labelScope = ast.NewScope(p.labelScope)
+	p.targetStack = append(p.targetStack, nil)
+}
+
+func (p *parser) closeLabelScope() {
+	// resolve labels
+	n := len(p.targetStack) - 1
+	scope := p.labelScope
+	for _, ident := range p.targetStack[n] {
+		ident.Obj = scope.Lookup(ident.Name)
+		if ident.Obj == nil && p.mode&DeclarationErrors != 0 {
+			p.error(ident.Pos(), fmt.Sprintf("label %s undefined", ident.Name))
+		}
+	}
+	// pop label scope
+	p.targetStack = p.targetStack[0:n]
+	p.labelScope = p.labelScope.Outer
+}
+
+func (p *parser) declare(decl, data interface{}, scope *ast.Scope, kind ast.ObjKind, idents ...*ast.Ident) {
+	for _, ident := range idents {
+		assert(ident.Obj == nil, "identifier already declared or resolved")
+		obj := ast.NewObj(kind, ident.Name)
+		// remember the corresponding declaration for redeclaration
+		// errors and global variable resolution/typechecking phase
+		obj.Decl = decl
+		obj.Data = data
+		ident.Obj = obj
+		if ident.Name != "_" {
+			if alt := scope.Insert(obj); alt != nil && p.mode&DeclarationErrors != 0 {
+				prevDecl := ""
+				if pos := alt.Pos(); pos.IsValid() {
+					prevDecl = fmt.Sprintf("\n\tprevious declaration at %s", p.file.Position(pos))
+				}
+				p.error(ident.Pos(), fmt.Sprintf("%s redeclared in this block%s", ident.Name, prevDecl))
+			}
+		}
+	}
+}
+
+func (p *parser) shortVarDecl(idents []*ast.Ident) {
+	// Go spec: A short variable declaration may redeclare variables
+	// provided they were originally declared in the same block with
+	// the same type, and at least one of the non-blank variables is new.
+	n := 0 // number of new variables
+	for _, ident := range idents {
+		assert(ident.Obj == nil, "identifier already declared or resolved")
+		obj := ast.NewObj(ast.Var, ident.Name)
+		// short var declarations cannot have redeclaration errors
+		// and are not global => no need to remember the respective
+		// declaration
+		ident.Obj = obj
+		if ident.Name != "_" {
+			if alt := p.topScope.Insert(obj); alt != nil {
+				ident.Obj = alt // redeclaration
+			} else {
+				n++ // new declaration
+			}
+		}
+	}
+	if n == 0 && p.mode&DeclarationErrors != 0 {
+		p.error(idents[0].Pos(), "no new variables on left side of :=")
+	}
+}
+
+// The unresolved object is a sentinel to mark identifiers that have been added
+// to the list of unresolved identifiers. The sentinel is only used for verifying
+// internal consistency.
+var unresolved = new(ast.Object)
+
+func (p *parser) resolve(x ast.Expr) {
+	// nothing to do if x is not an identifier or the blank identifier
+	ident, _ := x.(*ast.Ident)
+	if ident == nil {
+		return
+	}
+	assert(ident.Obj == nil, "identifier already declared or resolved")
+	if ident.Name == "_" {
+		return
+	}
+	// try to resolve the identifier
+	for s := p.topScope; s != nil; s = s.Outer {
+		if obj := s.Lookup(ident.Name); obj != nil {
+			ident.Obj = obj
+			return
+		}
+	}
+	// all local scopes are known, so any unresolved identifier
+	// must be found either in the file scope, package scope
+	// (perhaps in another file), or universe scope --- collect
+	// them so that they can be resolved later
+	ident.Obj = unresolved
+	p.unresolved = append(p.unresolved, ident)
+}
+
+// ----------------------------------------------------------------------------
+// Parsing support
+
+func (p *parser) printTrace(a ...interface{}) {
+	const dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " +
+		". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
+	const n = uint(len(dots))
+	pos := p.file.Position(p.pos)
+	fmt.Printf("%5d:%3d: ", pos.Line, pos.Column)
+	i := 2 * p.indent
+	for ; i > n; i -= n {
+		fmt.Print(dots)
+	}
+	fmt.Print(dots[0:i])
+	fmt.Println(a...)
+}
+
+func trace(p *parser, msg string) *parser {
+	p.printTrace(msg, "(")
+	p.indent++
+	return p
+}
+
+// Usage pattern: defer un(trace(p, "..."));
+func un(p *parser) {
+	p.indent--
+	p.printTrace(")")
+}
+
+// Advance to the next token.
+func (p *parser) next0() {
+	// Because of one-token look-ahead, print the previous token
+	// when tracing as it provides a more readable output. The
+	// very first token (!p.pos.IsValid()) is not initialized
+	// (it is token.ILLEGAL), so don't print it .
+	if p.trace && p.pos.IsValid() {
+		s := p.tok.String()
+		switch {
+		case p.tok.IsLiteral():
+			p.printTrace(s, p.lit)
+		case p.tok.IsOperator(), p.tok.IsKeyword():
+			p.printTrace("\"" + s + "\"")
+		default:
+			p.printTrace(s)
+		}
+	}
+
+	p.pos, p.tok, p.lit = p.scanner.Scan()
+}
+
+// Consume a comment and return it and the line on which it ends.
+func (p *parser) consumeComment() (comment *ast.Comment, endline int) {
+	// /*-style comments may end on a different line than where they start.
+	// Scan the comment for '\n' chars and adjust endline accordingly.
+	endline = p.file.Line(p.pos)
+	if p.lit[1] == '*' {
+		// don't use range here - no need to decode Unicode code points
+		for i := 0; i < len(p.lit); i++ {
+			if p.lit[i] == '\n' {
+				endline++
+			}
+		}
+	}
+
+	comment = &ast.Comment{p.pos, p.lit}
+	p.next0()
+
+	return
+}
+
+// Consume a group of adjacent comments, add it to the parser's
+// comments list, and return it together with the line at which
+// the last comment in the group ends. An empty line or non-comment
+// token terminates a comment group.
+//
+func (p *parser) consumeCommentGroup() (comments *ast.CommentGroup, endline int) {
+	var list []*ast.Comment
+	endline = p.file.Line(p.pos)
+	for p.tok == token.COMMENT && endline+1 >= p.file.Line(p.pos) {
+		var comment *ast.Comment
+		comment, endline = p.consumeComment()
+		list = append(list, comment)
+	}
+
+	// add comment group to the comments list
+	comments = &ast.CommentGroup{list}
+	p.comments = append(p.comments, comments)
+
+	return
+}
+
+// Advance to the next non-comment token. In the process, collect
+// any comment groups encountered, and remember the last lead and
+// and line comments.
+//
+// A lead comment is a comment group that starts and ends in a
+// line without any other tokens and that is followed by a non-comment
+// token on the line immediately after the comment group.
+//
+// A line comment is a comment group that follows a non-comment
+// token on the same line, and that has no tokens after it on the line
+// where it ends.
+//
+// Lead and line comments may be considered documentation that is
+// stored in the AST.
+//
+func (p *parser) next() {
+	p.leadComment = nil
+	p.lineComment = nil
+	line := p.file.Line(p.pos) // current line
+	p.next0()
+
+	if p.tok == token.COMMENT {
+		var comment *ast.CommentGroup
+		var endline int
+
+		if p.file.Line(p.pos) == line {
+			// The comment is on same line as the previous token; it
+			// cannot be a lead comment but may be a line comment.
+			comment, endline = p.consumeCommentGroup()
+			if p.file.Line(p.pos) != endline {
+				// The next token is on a different line, thus
+				// the last comment group is a line comment.
+				p.lineComment = comment
+			}
+		}
+
+		// consume successor comments, if any
+		endline = -1
+		for p.tok == token.COMMENT {
+			comment, endline = p.consumeCommentGroup()
+		}
+
+		if endline+1 == p.file.Line(p.pos) {
+			// The next token is following on the line immediately after the
+			// comment group, thus the last comment group is a lead comment.
+			p.leadComment = comment
+		}
+	}
+}
+
+func (p *parser) error(pos token.Pos, msg string) {
+	p.Error(p.file.Position(pos), msg)
+}
+
+func (p *parser) errorExpected(pos token.Pos, msg string) {
+	msg = "expected " + msg
+	if pos == p.pos {
+		// the error happened at the current position;
+		// make the error message more specific
+		if p.tok == token.SEMICOLON && p.lit[0] == '\n' {
+			msg += ", found newline"
+		} else {
+			msg += ", found '" + p.tok.String() + "'"
+			if p.tok.IsLiteral() {
+				msg += " " + p.lit
+			}
+		}
+	}
+	p.error(pos, msg)
+}
+
+func (p *parser) expect(tok token.Token) token.Pos {
+	pos := p.pos
+	if p.tok != tok {
+		p.errorExpected(pos, "'"+tok.String()+"'")
+	}
+	p.next() // make progress
+	return pos
+}
+
+func (p *parser) expectSemi() {
+	if p.tok != token.RPAREN && p.tok != token.RBRACE {
+		p.expect(token.SEMICOLON)
+	}
+}
+
+func assert(cond bool, msg string) {
+	if !cond {
+		panic("go/parser internal error: " + msg)
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Identifiers
+
+func (p *parser) parseIdent() *ast.Ident {
+	pos := p.pos
+	name := "_"
+	if p.tok == token.IDENT {
+		name = p.lit
+		p.next()
+	} else {
+		p.expect(token.IDENT) // use expect() error handling
+	}
+	return &ast.Ident{pos, name, nil}
+}
+
+func (p *parser) parseIdentList() (list []*ast.Ident) {
+	if p.trace {
+		defer un(trace(p, "IdentList"))
+	}
+
+	list = append(list, p.parseIdent())
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.parseIdent())
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Common productions
+
+// If lhs is set, result list elements which are identifiers are not resolved.
+func (p *parser) parseExprList(lhs bool) (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "ExpressionList"))
+	}
+
+	list = append(list, p.checkExpr(p.parseExpr(lhs)))
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.checkExpr(p.parseExpr(lhs)))
+	}
+
+	return
+}
+
+func (p *parser) parseLhsList() []ast.Expr {
+	list := p.parseExprList(true)
+	switch p.tok {
+	case token.DEFINE:
+		// lhs of a short variable declaration
+		p.shortVarDecl(p.makeIdentList(list))
+	case token.COLON:
+		// lhs of a label declaration or a communication clause of a select
+		// statement (parseLhsList is not called when parsing the case clause
+		// of a switch statement):
+		// - labels are declared by the caller of parseLhsList
+		// - for communication clauses, if there is a stand-alone identifier
+		//   followed by a colon, we have a syntax error; there is no need
+		//   to resolve the identifier in that case
+	default:
+		// identifiers must be declared elsewhere
+		for _, x := range list {
+			p.resolve(x)
+		}
+	}
+	return list
+}
+
+func (p *parser) parseRhsList() []ast.Expr {
+	return p.parseExprList(false)
+}
+
+// ----------------------------------------------------------------------------
+// Types
+
+func (p *parser) parseType() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Type"))
+	}
+
+	typ := p.tryType()
+
+	if typ == nil {
+		pos := p.pos
+		p.errorExpected(pos, "type")
+		p.next() // make progress
+		return &ast.BadExpr{pos, p.pos}
+	}
+
+	return typ
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) parseTypeName() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeName"))
+	}
+
+	ident := p.parseIdent()
+	// don't resolve ident yet - it may be a parameter or field name
+
+	if p.tok == token.PERIOD {
+		// ident is a package name
+		p.next()
+		p.resolve(ident)
+		sel := p.parseIdent()
+		return &ast.SelectorExpr{ident, sel}
+	}
+
+	return ident
+}
+
+func (p *parser) parseArrayType(ellipsisOk bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "ArrayType"))
+	}
+
+	lbrack := p.expect(token.LBRACK)
+	var len ast.Expr
+	if ellipsisOk && p.tok == token.ELLIPSIS {
+		len = &ast.Ellipsis{p.pos, nil}
+		p.next()
+	} else if p.tok != token.RBRACK {
+		len = p.parseRhs()
+	}
+	p.expect(token.RBRACK)
+	elt := p.parseType()
+
+	return &ast.ArrayType{lbrack, len, elt}
+}
+
+func (p *parser) makeIdentList(list []ast.Expr) []*ast.Ident {
+	idents := make([]*ast.Ident, len(list))
+	for i, x := range list {
+		ident, isIdent := x.(*ast.Ident)
+		if !isIdent {
+			pos := x.(ast.Expr).Pos()
+			p.errorExpected(pos, "identifier")
+			ident = &ast.Ident{pos, "_", nil}
+		}
+		idents[i] = ident
+	}
+	return idents
+}
+
+func (p *parser) parseFieldDecl(scope *ast.Scope) *ast.Field {
+	if p.trace {
+		defer un(trace(p, "FieldDecl"))
+	}
+
+	doc := p.leadComment
+
+	// fields
+	list, typ := p.parseVarList(false)
+
+	// optional tag
+	var tag *ast.BasicLit
+	if p.tok == token.STRING {
+		tag = &ast.BasicLit{p.pos, p.tok, p.lit}
+		p.next()
+	}
+
+	// analyze case
+	var idents []*ast.Ident
+	if typ != nil {
+		// IdentifierList Type
+		idents = p.makeIdentList(list)
+	} else {
+		// ["*"] TypeName (AnonymousField)
+		typ = list[0] // we always have at least one element
+		p.resolve(typ)
+		if n := len(list); n > 1 || !isTypeName(deref(typ)) {
+			pos := typ.Pos()
+			p.errorExpected(pos, "anonymous field")
+			typ = &ast.BadExpr{pos, list[n-1].End()}
+		}
+	}
+
+	p.expectSemi() // call before accessing p.linecomment
+
+	field := &ast.Field{doc, idents, typ, tag, p.lineComment}
+	p.declare(field, nil, scope, ast.Var, idents...)
+
+	return field
+}
+
+func (p *parser) parseStructType() *ast.StructType {
+	if p.trace {
+		defer un(trace(p, "StructType"))
+	}
+
+	pos := p.expect(token.STRUCT)
+	lbrace := p.expect(token.LBRACE)
+	scope := ast.NewScope(nil) // struct scope
+	var list []*ast.Field
+	for p.tok == token.IDENT || p.tok == token.MUL || p.tok == token.LPAREN {
+		// a field declaration cannot start with a '(' but we accept
+		// it here for more robust parsing and better error messages
+		// (parseFieldDecl will check and complain if necessary)
+		list = append(list, p.parseFieldDecl(scope))
+	}
+	rbrace := p.expect(token.RBRACE)
+
+	// TODO(gri): store struct scope in AST
+	return &ast.StructType{pos, &ast.FieldList{lbrace, list, rbrace}, false}
+}
+
+func (p *parser) parsePointerType() *ast.StarExpr {
+	if p.trace {
+		defer un(trace(p, "PointerType"))
+	}
+
+	star := p.expect(token.MUL)
+	base := p.parseType()
+
+	return &ast.StarExpr{star, base}
+}
+
+func (p *parser) tryVarType(isParam bool) ast.Expr {
+	if isParam && p.tok == token.ELLIPSIS {
+		pos := p.pos
+		p.next()
+		typ := p.tryIdentOrType(isParam) // don't use parseType so we can provide better error message
+		if typ == nil {
+			p.error(pos, "'...' parameter is missing type")
+			typ = &ast.BadExpr{pos, p.pos}
+		}
+		if p.tok != token.RPAREN {
+			p.error(pos, "can use '...' with last parameter type only")
+		}
+		return &ast.Ellipsis{pos, typ}
+	}
+	return p.tryIdentOrType(false)
+}
+
+func (p *parser) parseVarType(isParam bool) ast.Expr {
+	typ := p.tryVarType(isParam)
+	if typ == nil {
+		pos := p.pos
+		p.errorExpected(pos, "type")
+		p.next() // make progress
+		typ = &ast.BadExpr{pos, p.pos}
+	}
+	return typ
+}
+
+func (p *parser) parseVarList(isParam bool) (list []ast.Expr, typ ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "VarList"))
+	}
+
+	// a list of identifiers looks like a list of type names
+	for {
+		// parseVarType accepts any type (including parenthesized ones)
+		// even though the syntax does not permit them here: we
+		// accept them all for more robust parsing and complain
+		// afterwards
+		list = append(list, p.parseVarType(isParam))
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+	}
+
+	// if we had a list of identifiers, it must be followed by a type
+	typ = p.tryVarType(isParam)
+	if typ != nil {
+		p.resolve(typ)
+	}
+
+	return
+}
+
+func (p *parser) parseParameterList(scope *ast.Scope, ellipsisOk bool) (params []*ast.Field) {
+	if p.trace {
+		defer un(trace(p, "ParameterList"))
+	}
+
+	list, typ := p.parseVarList(ellipsisOk)
+	if typ != nil {
+		// IdentifierList Type
+		idents := p.makeIdentList(list)
+		field := &ast.Field{nil, idents, typ, nil, nil}
+		params = append(params, field)
+		// Go spec: The scope of an identifier denoting a function
+		// parameter or result variable is the function body.
+		p.declare(field, nil, scope, ast.Var, idents...)
+		if p.tok == token.COMMA {
+			p.next()
+		}
+
+		for p.tok != token.RPAREN && p.tok != token.EOF {
+			idents := p.parseIdentList()
+			typ := p.parseVarType(ellipsisOk)
+			field := &ast.Field{nil, idents, typ, nil, nil}
+			params = append(params, field)
+			// Go spec: The scope of an identifier denoting a function
+			// parameter or result variable is the function body.
+			p.declare(field, nil, scope, ast.Var, idents...)
+			if p.tok != token.COMMA {
+				break
+			}
+			p.next()
+		}
+
+	} else {
+		// Type { "," Type } (anonymous parameters)
+		params = make([]*ast.Field, len(list))
+		for i, x := range list {
+			p.resolve(x)
+			params[i] = &ast.Field{Type: x}
+		}
+	}
+
+	return
+}
+
+func (p *parser) parseParameters(scope *ast.Scope, ellipsisOk bool) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Parameters"))
+	}
+
+	var params []*ast.Field
+	lparen := p.expect(token.LPAREN)
+	if p.tok != token.RPAREN {
+		params = p.parseParameterList(scope, ellipsisOk)
+	}
+	rparen := p.expect(token.RPAREN)
+
+	return &ast.FieldList{lparen, params, rparen}
+}
+
+func (p *parser) parseResult(scope *ast.Scope) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Result"))
+	}
+
+	if p.tok == token.LPAREN {
+		return p.parseParameters(scope, false)
+	}
+
+	typ := p.tryType()
+	if typ != nil {
+		list := make([]*ast.Field, 1)
+		list[0] = &ast.Field{Type: typ}
+		return &ast.FieldList{List: list}
+	}
+
+	return nil
+}
+
+func (p *parser) parseSignature(scope *ast.Scope) (params, results *ast.FieldList) {
+	if p.trace {
+		defer un(trace(p, "Signature"))
+	}
+
+	params = p.parseParameters(scope, true)
+	results = p.parseResult(scope)
+
+	return
+}
+
+func (p *parser) parseFuncType() (*ast.FuncType, *ast.Scope) {
+	if p.trace {
+		defer un(trace(p, "FuncType"))
+	}
+
+	pos := p.expect(token.FUNC)
+	scope := ast.NewScope(p.topScope) // function scope
+	params, results := p.parseSignature(scope)
+
+	return &ast.FuncType{pos, params, results}, scope
+}
+
+func (p *parser) parseMethodSpec(scope *ast.Scope) *ast.Field {
+	if p.trace {
+		defer un(trace(p, "MethodSpec"))
+	}
+
+	doc := p.leadComment
+	var idents []*ast.Ident
+	var typ ast.Expr
+	x := p.parseTypeName()
+	if ident, isIdent := x.(*ast.Ident); isIdent && p.tok == token.LPAREN {
+		// method
+		idents = []*ast.Ident{ident}
+		scope := ast.NewScope(nil) // method scope
+		params, results := p.parseSignature(scope)
+		typ = &ast.FuncType{token.NoPos, params, results}
+	} else {
+		// embedded interface
+		typ = x
+		p.resolve(typ)
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	spec := &ast.Field{doc, idents, typ, nil, p.lineComment}
+	p.declare(spec, nil, scope, ast.Fun, idents...)
+
+	return spec
+}
+
+func (p *parser) parseInterfaceType() *ast.InterfaceType {
+	if p.trace {
+		defer un(trace(p, "InterfaceType"))
+	}
+
+	pos := p.expect(token.INTERFACE)
+	lbrace := p.expect(token.LBRACE)
+	scope := ast.NewScope(nil) // interface scope
+	var list []*ast.Field
+	for p.tok == token.IDENT {
+		list = append(list, p.parseMethodSpec(scope))
+	}
+	rbrace := p.expect(token.RBRACE)
+
+	// TODO(gri): store interface scope in AST
+	return &ast.InterfaceType{pos, &ast.FieldList{lbrace, list, rbrace}, false}
+}
+
+func (p *parser) parseMapType() *ast.MapType {
+	if p.trace {
+		defer un(trace(p, "MapType"))
+	}
+
+	pos := p.expect(token.MAP)
+	p.expect(token.LBRACK)
+	key := p.parseType()
+	p.expect(token.RBRACK)
+	value := p.parseType()
+
+	return &ast.MapType{pos, key, value}
+}
+
+func (p *parser) parseChanType() *ast.ChanType {
+	if p.trace {
+		defer un(trace(p, "ChanType"))
+	}
+
+	pos := p.pos
+	dir := ast.SEND | ast.RECV
+	if p.tok == token.CHAN {
+		p.next()
+		if p.tok == token.ARROW {
+			p.next()
+			dir = ast.SEND
+		}
+	} else {
+		p.expect(token.ARROW)
+		p.expect(token.CHAN)
+		dir = ast.RECV
+	}
+	value := p.parseType()
+
+	return &ast.ChanType{pos, dir, value}
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) tryIdentOrType(ellipsisOk bool) ast.Expr {
+	switch p.tok {
+	case token.IDENT:
+		return p.parseTypeName()
+	case token.LBRACK:
+		return p.parseArrayType(ellipsisOk)
+	case token.STRUCT:
+		return p.parseStructType()
+	case token.MUL:
+		return p.parsePointerType()
+	case token.FUNC:
+		typ, _ := p.parseFuncType()
+		return typ
+	case token.INTERFACE:
+		return p.parseInterfaceType()
+	case token.MAP:
+		return p.parseMapType()
+	case token.CHAN, token.ARROW:
+		return p.parseChanType()
+	case token.LPAREN:
+		lparen := p.pos
+		p.next()
+		typ := p.parseType()
+		rparen := p.expect(token.RPAREN)
+		return &ast.ParenExpr{lparen, typ, rparen}
+	}
+
+	// no type found
+	return nil
+}
+
+func (p *parser) tryType() ast.Expr {
+	typ := p.tryIdentOrType(false)
+	if typ != nil {
+		p.resolve(typ)
+	}
+	return typ
+}
+
+// ----------------------------------------------------------------------------
+// Blocks
+
+func (p *parser) parseStmtList() (list []ast.Stmt) {
+	if p.trace {
+		defer un(trace(p, "StatementList"))
+	}
+
+	for p.tok != token.CASE && p.tok != token.DEFAULT && p.tok != token.RBRACE && p.tok != token.EOF {
+		list = append(list, p.parseStmt())
+	}
+
+	return
+}
+
+func (p *parser) parseBody(scope *ast.Scope) *ast.BlockStmt {
+	if p.trace {
+		defer un(trace(p, "Body"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	p.topScope = scope // open function scope
+	p.openLabelScope()
+	list := p.parseStmtList()
+	p.closeLabelScope()
+	p.closeScope()
+	rbrace := p.expect(token.RBRACE)
+
+	return &ast.BlockStmt{lbrace, list, rbrace}
+}
+
+func (p *parser) parseBlockStmt() *ast.BlockStmt {
+	if p.trace {
+		defer un(trace(p, "BlockStmt"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	p.openScope()
+	list := p.parseStmtList()
+	p.closeScope()
+	rbrace := p.expect(token.RBRACE)
+
+	return &ast.BlockStmt{lbrace, list, rbrace}
+}
+
+// ----------------------------------------------------------------------------
+// Expressions
+
+func (p *parser) parseFuncTypeOrLit() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "FuncTypeOrLit"))
+	}
+
+	typ, scope := p.parseFuncType()
+	if p.tok != token.LBRACE {
+		// function type only
+		return typ
+	}
+
+	p.exprLev++
+	body := p.parseBody(scope)
+	p.exprLev--
+
+	return &ast.FuncLit{typ, body}
+}
+
+// parseOperand may return an expression or a raw type (incl. array
+// types of the form [...]T. Callers must verify the result.
+// If lhs is set and the result is an identifier, it is not resolved.
+//
+func (p *parser) parseOperand(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Operand"))
+	}
+
+	switch p.tok {
+	case token.IDENT:
+		x := p.parseIdent()
+		if !lhs {
+			p.resolve(x)
+		}
+		return x
+
+	case token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING:
+		x := &ast.BasicLit{p.pos, p.tok, p.lit}
+		p.next()
+		return x
+
+	case token.LPAREN:
+		lparen := p.pos
+		p.next()
+		p.exprLev++
+		x := p.parseRhsOrType() // types may be parenthesized: (some type)
+		p.exprLev--
+		rparen := p.expect(token.RPAREN)
+		return &ast.ParenExpr{lparen, x, rparen}
+
+	case token.FUNC:
+		return p.parseFuncTypeOrLit()
+
+	default:
+		if typ := p.tryIdentOrType(true); typ != nil {
+			// could be type for composite literal or conversion
+			_, isIdent := typ.(*ast.Ident)
+			assert(!isIdent, "type cannot be identifier")
+			return typ
+		}
+	}
+
+	pos := p.pos
+	p.errorExpected(pos, "operand")
+	p.next() // make progress
+	return &ast.BadExpr{pos, p.pos}
+}
+
+func (p *parser) parseSelector(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Selector"))
+	}
+
+	sel := p.parseIdent()
+
+	return &ast.SelectorExpr{x, sel}
+}
+
+func (p *parser) parseTypeAssertion(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeAssertion"))
+	}
+
+	p.expect(token.LPAREN)
+	var typ ast.Expr
+	if p.tok == token.TYPE {
+		// type switch: typ == nil
+		p.next()
+	} else {
+		typ = p.parseType()
+	}
+	p.expect(token.RPAREN)
+
+	return &ast.TypeAssertExpr{x, typ}
+}
+
+func (p *parser) parseIndexOrSlice(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "IndexOrSlice"))
+	}
+
+	lbrack := p.expect(token.LBRACK)
+	p.exprLev++
+	var low, high ast.Expr
+	isSlice := false
+	if p.tok != token.COLON {
+		low = p.parseRhs()
+	}
+	if p.tok == token.COLON {
+		isSlice = true
+		p.next()
+		if p.tok != token.RBRACK {
+			high = p.parseRhs()
+		}
+	}
+	p.exprLev--
+	rbrack := p.expect(token.RBRACK)
+
+	if isSlice {
+		return &ast.SliceExpr{x, lbrack, low, high, rbrack}
+	}
+	return &ast.IndexExpr{x, lbrack, low, rbrack}
+}
+
+func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
+	if p.trace {
+		defer un(trace(p, "CallOrConversion"))
+	}
+
+	lparen := p.expect(token.LPAREN)
+	p.exprLev++
+	var list []ast.Expr
+	var ellipsis token.Pos
+	for p.tok != token.RPAREN && p.tok != token.EOF && !ellipsis.IsValid() {
+		list = append(list, p.parseRhsOrType()) // builtins may expect a type: make(some type, ...)
+		if p.tok == token.ELLIPSIS {
+			ellipsis = p.pos
+			p.next()
+		}
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+	}
+	p.exprLev--
+	rparen := p.expect(token.RPAREN)
+
+	return &ast.CallExpr{fun, lparen, list, ellipsis, rparen}
+}
+
+func (p *parser) parseElement(keyOk bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Element"))
+	}
+
+	if p.tok == token.LBRACE {
+		return p.parseLiteralValue(nil)
+	}
+
+	x := p.checkExpr(p.parseExpr(keyOk)) // don't resolve if map key
+	if keyOk {
+		if p.tok == token.COLON {
+			colon := p.pos
+			p.next()
+			return &ast.KeyValueExpr{x, colon, p.parseElement(false)}
+		}
+		p.resolve(x) // not a map key
+	}
+
+	return x
+}
+
+func (p *parser) parseElementList() (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "ElementList"))
+	}
+
+	for p.tok != token.RBRACE && p.tok != token.EOF {
+		list = append(list, p.parseElement(true))
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+	}
+
+	return
+}
+
+func (p *parser) parseLiteralValue(typ ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "LiteralValue"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	var elts []ast.Expr
+	p.exprLev++
+	if p.tok != token.RBRACE {
+		elts = p.parseElementList()
+	}
+	p.exprLev--
+	rbrace := p.expect(token.RBRACE)
+	return &ast.CompositeLit{typ, lbrace, elts, rbrace}
+}
+
+// checkExpr checks that x is an expression (and not a type).
+func (p *parser) checkExpr(x ast.Expr) ast.Expr {
+	switch t := unparen(x).(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.BasicLit:
+	case *ast.FuncLit:
+	case *ast.CompositeLit:
+	case *ast.ParenExpr:
+		panic("unreachable")
+	case *ast.SelectorExpr:
+	case *ast.IndexExpr:
+	case *ast.SliceExpr:
+	case *ast.TypeAssertExpr:
+		// If t.Type == nil we have a type assertion of the form
+		// y.(type), which is only allowed in type switch expressions.
+		// It's hard to exclude those but for the case where we are in
+		// a type switch. Instead be lenient and test this in the type
+		// checker.
+	case *ast.CallExpr:
+	case *ast.StarExpr:
+	case *ast.UnaryExpr:
+	case *ast.BinaryExpr:
+	default:
+		// all other nodes are not proper expressions
+		p.errorExpected(x.Pos(), "expression")
+		x = &ast.BadExpr{x.Pos(), x.End()}
+	}
+	return x
+}
+
+// isTypeName returns true iff x is a (qualified) TypeName.
+func isTypeName(x ast.Expr) bool {
+	switch t := x.(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.SelectorExpr:
+		_, isIdent := t.X.(*ast.Ident)
+		return isIdent
+	default:
+		return false // all other nodes are not type names
+	}
+	return true
+}
+
+// isLiteralType returns true iff x is a legal composite literal type.
+func isLiteralType(x ast.Expr) bool {
+	switch t := x.(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.SelectorExpr:
+		_, isIdent := t.X.(*ast.Ident)
+		return isIdent
+	case *ast.ArrayType:
+	case *ast.StructType:
+	case *ast.MapType:
+	default:
+		return false // all other nodes are not legal composite literal types
+	}
+	return true
+}
+
+// If x is of the form *T, deref returns T, otherwise it returns x.
+func deref(x ast.Expr) ast.Expr {
+	if p, isPtr := x.(*ast.StarExpr); isPtr {
+		x = p.X
+	}
+	return x
+}
+
+// If x is of the form (T), unparen returns unparen(T), otherwise it returns x.
+func unparen(x ast.Expr) ast.Expr {
+	if p, isParen := x.(*ast.ParenExpr); isParen {
+		x = unparen(p.X)
+	}
+	return x
+}
+
+// checkExprOrType checks that x is an expression or a type
+// (and not a raw type such as [...]T).
+//
+func (p *parser) checkExprOrType(x ast.Expr) ast.Expr {
+	switch t := unparen(x).(type) {
+	case *ast.ParenExpr:
+		panic("unreachable")
+	case *ast.UnaryExpr:
+	case *ast.ArrayType:
+		if len, isEllipsis := t.Len.(*ast.Ellipsis); isEllipsis {
+			p.error(len.Pos(), "expected array length, found '...'")
+			x = &ast.BadExpr{x.Pos(), x.End()}
+		}
+	}
+
+	// all other nodes are expressions or types
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parsePrimaryExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "PrimaryExpr"))
+	}
+
+	x := p.parseOperand(lhs)
+L:
+	for {
+		switch p.tok {
+		case token.PERIOD:
+			p.next()
+			if lhs {
+				p.resolve(x)
+			}
+			switch p.tok {
+			case token.IDENT:
+				x = p.parseSelector(p.checkExpr(x))
+			case token.LPAREN:
+				x = p.parseTypeAssertion(p.checkExpr(x))
+			default:
+				pos := p.pos
+				p.next() // make progress
+				p.errorExpected(pos, "selector or type assertion")
+				x = &ast.BadExpr{pos, p.pos}
+			}
+		case token.LBRACK:
+			if lhs {
+				p.resolve(x)
+			}
+			x = p.parseIndexOrSlice(p.checkExpr(x))
+		case token.LPAREN:
+			if lhs {
+				p.resolve(x)
+			}
+			x = p.parseCallOrConversion(p.checkExprOrType(x))
+		case token.LBRACE:
+			if isLiteralType(x) && (p.exprLev >= 0 || !isTypeName(x)) {
+				if lhs {
+					p.resolve(x)
+				}
+				x = p.parseLiteralValue(x)
+			} else {
+				break L
+			}
+		default:
+			break L
+		}
+		lhs = false // no need to try to resolve again
+	}
+
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parseUnaryExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "UnaryExpr"))
+	}
+
+	switch p.tok {
+	case token.ADD, token.SUB, token.NOT, token.XOR, token.AND:
+		pos, op := p.pos, p.tok
+		p.next()
+		x := p.parseUnaryExpr(false)
+		return &ast.UnaryExpr{pos, op, p.checkExpr(x)}
+
+	case token.ARROW:
+		// channel type or receive expression
+		pos := p.pos
+		p.next()
+		if p.tok == token.CHAN {
+			p.next()
+			value := p.parseType()
+			return &ast.ChanType{pos, ast.RECV, value}
+		}
+
+		x := p.parseUnaryExpr(false)
+		return &ast.UnaryExpr{pos, token.ARROW, p.checkExpr(x)}
+
+	case token.MUL:
+		// pointer type or unary "*" expression
+		pos := p.pos
+		p.next()
+		x := p.parseUnaryExpr(false)
+		return &ast.StarExpr{pos, p.checkExprOrType(x)}
+	}
+
+	return p.parsePrimaryExpr(lhs)
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parseBinaryExpr(lhs bool, prec1 int) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "BinaryExpr"))
+	}
+
+	x := p.parseUnaryExpr(lhs)
+	for prec := p.tok.Precedence(); prec >= prec1; prec-- {
+		for p.tok.Precedence() == prec {
+			pos, op := p.pos, p.tok
+			p.next()
+			if lhs {
+				p.resolve(x)
+				lhs = false
+			}
+			y := p.parseBinaryExpr(false, prec+1)
+			x = &ast.BinaryExpr{p.checkExpr(x), pos, op, p.checkExpr(y)}
+		}
+	}
+
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+// The result may be a type or even a raw type ([...]int). Callers must
+// check the result (using checkExpr or checkExprOrType), depending on
+// context.
+func (p *parser) parseExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Expression"))
+	}
+
+	return p.parseBinaryExpr(lhs, token.LowestPrec+1)
+}
+
+func (p *parser) parseRhs() ast.Expr {
+	return p.checkExpr(p.parseExpr(false))
+}
+
+func (p *parser) parseRhsOrType() ast.Expr {
+	return p.checkExprOrType(p.parseExpr(false))
+}
+
+// ----------------------------------------------------------------------------
+// Statements
+
+// Parsing modes for parseSimpleStmt.
+const (
+	basic = iota
+	labelOk
+	rangeOk
+)
+
+// parseSimpleStmt returns true as 2nd result if it parsed the assignment
+// of a range clause (with mode == rangeOk). The returned statement is an
+// assignment with a right-hand side that is a single unary expression of
+// the form "range x". No guarantees are given for the left-hand side.
+func (p *parser) parseSimpleStmt(mode int) (ast.Stmt, bool) {
+	if p.trace {
+		defer un(trace(p, "SimpleStmt"))
+	}
+
+	x := p.parseLhsList()
+
+	switch p.tok {
+	case
+		token.DEFINE, token.ASSIGN, token.ADD_ASSIGN,
+		token.SUB_ASSIGN, token.MUL_ASSIGN, token.QUO_ASSIGN,
+		token.REM_ASSIGN, token.AND_ASSIGN, token.OR_ASSIGN,
+		token.XOR_ASSIGN, token.SHL_ASSIGN, token.SHR_ASSIGN, token.AND_NOT_ASSIGN:
+		// assignment statement, possibly part of a range clause
+		pos, tok := p.pos, p.tok
+		p.next()
+		var y []ast.Expr
+		isRange := false
+		if mode == rangeOk && p.tok == token.RANGE && (tok == token.DEFINE || tok == token.ASSIGN) {
+			pos := p.pos
+			p.next()
+			y = []ast.Expr{&ast.UnaryExpr{pos, token.RANGE, p.parseRhs()}}
+			isRange = true
+		} else {
+			y = p.parseRhsList()
+		}
+		return &ast.AssignStmt{x, pos, tok, y}, isRange
+	}
+
+	if len(x) > 1 {
+		p.errorExpected(x[0].Pos(), "1 expression")
+		// continue with first expression
+	}
+
+	switch p.tok {
+	case token.COLON:
+		// labeled statement
+		colon := p.pos
+		p.next()
+		if label, isIdent := x[0].(*ast.Ident); mode == labelOk && isIdent {
+			// Go spec: The scope of a label is the body of the function
+			// in which it is declared and excludes the body of any nested
+			// function.
+			stmt := &ast.LabeledStmt{label, colon, p.parseStmt()}
+			p.declare(stmt, nil, p.labelScope, ast.Lbl, label)
+			return stmt, false
+		}
+		// The label declaration typically starts at x[0].Pos(), but the label
+		// declaration may be erroneous due to a token after that position (and
+		// before the ':'). If SpuriousErrors is not set, the (only) error re-
+		// ported for the line is the illegal label error instead of the token
+		// before the ':' that caused the problem. Thus, use the (latest) colon
+		// position for error reporting.
+		p.error(colon, "illegal label declaration")
+		return &ast.BadStmt{x[0].Pos(), colon + 1}, false
+
+	case token.ARROW:
+		// send statement
+		arrow := p.pos
+		p.next() // consume "<-"
+		y := p.parseRhs()
+		return &ast.SendStmt{x[0], arrow, y}, false
+
+	case token.INC, token.DEC:
+		// increment or decrement
+		s := &ast.IncDecStmt{x[0], p.pos, p.tok}
+		p.next() // consume "++" or "--"
+		return s, false
+	}
+
+	// expression
+	return &ast.ExprStmt{x[0]}, false
+}
+
+func (p *parser) parseCallExpr() *ast.CallExpr {
+	x := p.parseRhsOrType() // could be a conversion: (some type)(x)
+	if call, isCall := x.(*ast.CallExpr); isCall {
+		return call
+	}
+	p.errorExpected(x.Pos(), "function/method call")
+	return nil
+}
+
+func (p *parser) parseGoStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "GoStmt"))
+	}
+
+	pos := p.expect(token.GO)
+	call := p.parseCallExpr()
+	p.expectSemi()
+	if call == nil {
+		return &ast.BadStmt{pos, pos + 2} // len("go")
+	}
+
+	return &ast.GoStmt{pos, call}
+}
+
+func (p *parser) parseDeferStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "DeferStmt"))
+	}
+
+	pos := p.expect(token.DEFER)
+	call := p.parseCallExpr()
+	p.expectSemi()
+	if call == nil {
+		return &ast.BadStmt{pos, pos + 5} // len("defer")
+	}
+
+	return &ast.DeferStmt{pos, call}
+}
+
+func (p *parser) parseReturnStmt() *ast.ReturnStmt {
+	if p.trace {
+		defer un(trace(p, "ReturnStmt"))
+	}
+
+	pos := p.pos
+	p.expect(token.RETURN)
+	var x []ast.Expr
+	if p.tok != token.SEMICOLON && p.tok != token.RBRACE {
+		x = p.parseRhsList()
+	}
+	p.expectSemi()
+
+	return &ast.ReturnStmt{pos, x}
+}
+
+func (p *parser) parseBranchStmt(tok token.Token) *ast.BranchStmt {
+	if p.trace {
+		defer un(trace(p, "BranchStmt"))
+	}
+
+	pos := p.expect(tok)
+	var label *ast.Ident
+	if tok != token.FALLTHROUGH && p.tok == token.IDENT {
+		label = p.parseIdent()
+		// add to list of unresolved targets
+		n := len(p.targetStack) - 1
+		p.targetStack[n] = append(p.targetStack[n], label)
+	}
+	p.expectSemi()
+
+	return &ast.BranchStmt{pos, tok, label}
+}
+
+func (p *parser) makeExpr(s ast.Stmt) ast.Expr {
+	if s == nil {
+		return nil
+	}
+	if es, isExpr := s.(*ast.ExprStmt); isExpr {
+		return p.checkExpr(es.X)
+	}
+	p.error(s.Pos(), "expected condition, found simple statement")
+	return &ast.BadExpr{s.Pos(), s.End()}
+}
+
+func (p *parser) parseIfStmt() *ast.IfStmt {
+	if p.trace {
+		defer un(trace(p, "IfStmt"))
+	}
+
+	pos := p.expect(token.IF)
+	p.openScope()
+	defer p.closeScope()
+
+	var s ast.Stmt
+	var x ast.Expr
+	{
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok == token.SEMICOLON {
+			p.next()
+			x = p.parseRhs()
+		} else {
+			s, _ = p.parseSimpleStmt(basic)
+			if p.tok == token.SEMICOLON {
+				p.next()
+				x = p.parseRhs()
+			} else {
+				x = p.makeExpr(s)
+				s = nil
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	body := p.parseBlockStmt()
+	var else_ ast.Stmt
+	if p.tok == token.ELSE {
+		p.next()
+		else_ = p.parseStmt()
+	} else {
+		p.expectSemi()
+	}
+
+	return &ast.IfStmt{pos, s, x, body, else_}
+}
+
+func (p *parser) parseTypeList() (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "TypeList"))
+	}
+
+	list = append(list, p.parseType())
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.parseType())
+	}
+
+	return
+}
+
+func (p *parser) parseCaseClause(exprSwitch bool) *ast.CaseClause {
+	if p.trace {
+		defer un(trace(p, "CaseClause"))
+	}
+
+	pos := p.pos
+	var list []ast.Expr
+	if p.tok == token.CASE {
+		p.next()
+		if exprSwitch {
+			list = p.parseRhsList()
+		} else {
+			list = p.parseTypeList()
+		}
+	} else {
+		p.expect(token.DEFAULT)
+	}
+
+	colon := p.expect(token.COLON)
+	p.openScope()
+	body := p.parseStmtList()
+	p.closeScope()
+
+	return &ast.CaseClause{pos, list, colon, body}
+}
+
+func isExprSwitch(s ast.Stmt) bool {
+	if s == nil {
+		return true
+	}
+	if e, ok := s.(*ast.ExprStmt); ok {
+		if a, ok := e.X.(*ast.TypeAssertExpr); ok {
+			return a.Type != nil // regular type assertion
+		}
+		return true
+	}
+	return false
+}
+
+func (p *parser) parseSwitchStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "SwitchStmt"))
+	}
+
+	pos := p.expect(token.SWITCH)
+	p.openScope()
+	defer p.closeScope()
+
+	var s1, s2 ast.Stmt
+	if p.tok != token.LBRACE {
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok != token.SEMICOLON {
+			s2, _ = p.parseSimpleStmt(basic)
+		}
+		if p.tok == token.SEMICOLON {
+			p.next()
+			s1 = s2
+			s2 = nil
+			if p.tok != token.LBRACE {
+				s2, _ = p.parseSimpleStmt(basic)
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	exprSwitch := isExprSwitch(s2)
+	lbrace := p.expect(token.LBRACE)
+	var list []ast.Stmt
+	for p.tok == token.CASE || p.tok == token.DEFAULT {
+		list = append(list, p.parseCaseClause(exprSwitch))
+	}
+	rbrace := p.expect(token.RBRACE)
+	p.expectSemi()
+	body := &ast.BlockStmt{lbrace, list, rbrace}
+
+	if exprSwitch {
+		return &ast.SwitchStmt{pos, s1, p.makeExpr(s2), body}
+	}
+	// type switch
+	// TODO(gri): do all the checks!
+	return &ast.TypeSwitchStmt{pos, s1, s2, body}
+}
+
+func (p *parser) parseCommClause() *ast.CommClause {
+	if p.trace {
+		defer un(trace(p, "CommClause"))
+	}
+
+	p.openScope()
+	pos := p.pos
+	var comm ast.Stmt
+	if p.tok == token.CASE {
+		p.next()
+		lhs := p.parseLhsList()
+		if p.tok == token.ARROW {
+			// SendStmt
+			if len(lhs) > 1 {
+				p.errorExpected(lhs[0].Pos(), "1 expression")
+				// continue with first expression
+			}
+			arrow := p.pos
+			p.next()
+			rhs := p.parseRhs()
+			comm = &ast.SendStmt{lhs[0], arrow, rhs}
+		} else {
+			// RecvStmt
+			pos := p.pos
+			tok := p.tok
+			var rhs ast.Expr
+			if tok == token.ASSIGN || tok == token.DEFINE {
+				// RecvStmt with assignment
+				if len(lhs) > 2 {
+					p.errorExpected(lhs[0].Pos(), "1 or 2 expressions")
+					// continue with first two expressions
+					lhs = lhs[0:2]
+				}
+				p.next()
+				rhs = p.parseRhs()
+			} else {
+				// rhs must be single receive operation
+				if len(lhs) > 1 {
+					p.errorExpected(lhs[0].Pos(), "1 expression")
+					// continue with first expression
+				}
+				rhs = lhs[0]
+				lhs = nil // there is no lhs
+			}
+			if lhs != nil {
+				comm = &ast.AssignStmt{lhs, pos, tok, []ast.Expr{rhs}}
+			} else {
+				comm = &ast.ExprStmt{rhs}
+			}
+		}
+	} else {
+		p.expect(token.DEFAULT)
+	}
+
+	colon := p.expect(token.COLON)
+	body := p.parseStmtList()
+	p.closeScope()
+
+	return &ast.CommClause{pos, comm, colon, body}
+}
+
+func (p *parser) parseSelectStmt() *ast.SelectStmt {
+	if p.trace {
+		defer un(trace(p, "SelectStmt"))
+	}
+
+	pos := p.expect(token.SELECT)
+	lbrace := p.expect(token.LBRACE)
+	var list []ast.Stmt
+	for p.tok == token.CASE || p.tok == token.DEFAULT {
+		list = append(list, p.parseCommClause())
+	}
+	rbrace := p.expect(token.RBRACE)
+	p.expectSemi()
+	body := &ast.BlockStmt{lbrace, list, rbrace}
+
+	return &ast.SelectStmt{pos, body}
+}
+
+func (p *parser) parseForStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "ForStmt"))
+	}
+
+	pos := p.expect(token.FOR)
+	p.openScope()
+	defer p.closeScope()
+
+	var s1, s2, s3 ast.Stmt
+	var isRange bool
+	if p.tok != token.LBRACE {
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok != token.SEMICOLON {
+			s2, isRange = p.parseSimpleStmt(rangeOk)
+		}
+		if !isRange && p.tok == token.SEMICOLON {
+			p.next()
+			s1 = s2
+			s2 = nil
+			if p.tok != token.SEMICOLON {
+				s2, _ = p.parseSimpleStmt(basic)
+			}
+			p.expectSemi()
+			if p.tok != token.LBRACE {
+				s3, _ = p.parseSimpleStmt(basic)
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	body := p.parseBlockStmt()
+	p.expectSemi()
+
+	if isRange {
+		as := s2.(*ast.AssignStmt)
+		// check lhs
+		var key, value ast.Expr
+		switch len(as.Lhs) {
+		case 2:
+			key, value = as.Lhs[0], as.Lhs[1]
+		case 1:
+			key = as.Lhs[0]
+		default:
+			p.errorExpected(as.Lhs[0].Pos(), "1 or 2 expressions")
+			return &ast.BadStmt{pos, body.End()}
+		}
+		// parseSimpleStmt returned a right-hand side that
+		// is a single unary expression of the form "range x"
+		x := as.Rhs[0].(*ast.UnaryExpr).X
+		return &ast.RangeStmt{pos, key, value, as.TokPos, as.Tok, x, body}
+	}
+
+	// regular for statement
+	return &ast.ForStmt{pos, s1, p.makeExpr(s2), s3, body}
+}
+
+func (p *parser) parseStmt() (s ast.Stmt) {
+	if p.trace {
+		defer un(trace(p, "Statement"))
+	}
+
+	switch p.tok {
+	case token.CONST, token.TYPE, token.VAR:
+		s = &ast.DeclStmt{p.parseDecl()}
+	case
+		// tokens that may start a top-level expression
+		token.IDENT, token.INT, token.FLOAT, token.CHAR, token.STRING, token.FUNC, token.LPAREN, // operand
+		token.LBRACK, token.STRUCT, // composite type
+		token.MUL, token.AND, token.ARROW, token.ADD, token.SUB, token.XOR: // unary operators
+		s, _ = p.parseSimpleStmt(labelOk)
+		// because of the required look-ahead, labeled statements are
+		// parsed by parseSimpleStmt - don't expect a semicolon after
+		// them
+		if _, isLabeledStmt := s.(*ast.LabeledStmt); !isLabeledStmt {
+			p.expectSemi()
+		}
+	case token.GO:
+		s = p.parseGoStmt()
+	case token.DEFER:
+		s = p.parseDeferStmt()
+	case token.RETURN:
+		s = p.parseReturnStmt()
+	case token.BREAK, token.CONTINUE, token.GOTO, token.FALLTHROUGH:
+		s = p.parseBranchStmt(p.tok)
+	case token.LBRACE:
+		s = p.parseBlockStmt()
+		p.expectSemi()
+	case token.IF:
+		s = p.parseIfStmt()
+	case token.SWITCH:
+		s = p.parseSwitchStmt()
+	case token.SELECT:
+		s = p.parseSelectStmt()
+	case token.FOR:
+		s = p.parseForStmt()
+	case token.SEMICOLON:
+		s = &ast.EmptyStmt{p.pos}
+		p.next()
+	case token.RBRACE:
+		// a semicolon may be omitted before a closing "}"
+		s = &ast.EmptyStmt{p.pos}
+	default:
+		// no statement found
+		pos := p.pos
+		p.errorExpected(pos, "statement")
+		p.next() // make progress
+		s = &ast.BadStmt{pos, p.pos}
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Declarations
+
+type parseSpecFunction func(p *parser, doc *ast.CommentGroup, iota int) ast.Spec
+
+func parseImportSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "ImportSpec"))
+	}
+
+	var ident *ast.Ident
+	switch p.tok {
+	case token.PERIOD:
+		ident = &ast.Ident{p.pos, ".", nil}
+		p.next()
+	case token.IDENT:
+		ident = p.parseIdent()
+	}
+
+	var path *ast.BasicLit
+	if p.tok == token.STRING {
+		path = &ast.BasicLit{p.pos, p.tok, p.lit}
+		p.next()
+	} else {
+		p.expect(token.STRING) // use expect() error handling
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	// collect imports
+	spec := &ast.ImportSpec{doc, ident, path, p.lineComment}
+	p.imports = append(p.imports, spec)
+
+	return spec
+}
+
+func parseConstSpec(p *parser, doc *ast.CommentGroup, iota int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "ConstSpec"))
+	}
+
+	idents := p.parseIdentList()
+	typ := p.tryType()
+	var values []ast.Expr
+	if typ != nil || p.tok == token.ASSIGN || iota == 0 {
+		p.expect(token.ASSIGN)
+		values = p.parseRhsList()
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	// Go spec: The scope of a constant or variable identifier declared inside
+	// a function begins at the end of the ConstSpec or VarSpec and ends at
+	// the end of the innermost containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.ValueSpec{doc, idents, typ, values, p.lineComment}
+	p.declare(spec, iota, p.topScope, ast.Con, idents...)
+
+	return spec
+}
+
+func parseTypeSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "TypeSpec"))
+	}
+
+	ident := p.parseIdent()
+
+	// Go spec: The scope of a type identifier declared inside a function begins
+	// at the identifier in the TypeSpec and ends at the end of the innermost
+	// containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.TypeSpec{doc, ident, nil, nil}
+	p.declare(spec, nil, p.topScope, ast.Typ, ident)
+
+	spec.Type = p.parseType()
+	p.expectSemi() // call before accessing p.linecomment
+	spec.Comment = p.lineComment
+
+	return spec
+}
+
+func parseVarSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "VarSpec"))
+	}
+
+	idents := p.parseIdentList()
+	typ := p.tryType()
+	var values []ast.Expr
+	if typ == nil || p.tok == token.ASSIGN {
+		p.expect(token.ASSIGN)
+		values = p.parseRhsList()
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	// Go spec: The scope of a constant or variable identifier declared inside
+	// a function begins at the end of the ConstSpec or VarSpec and ends at
+	// the end of the innermost containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.ValueSpec{doc, idents, typ, values, p.lineComment}
+	p.declare(spec, nil, p.topScope, ast.Var, idents...)
+
+	return spec
+}
+
+func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction) *ast.GenDecl {
+	if p.trace {
+		defer un(trace(p, "GenDecl("+keyword.String()+")"))
+	}
+
+	doc := p.leadComment
+	pos := p.expect(keyword)
+	var lparen, rparen token.Pos
+	var list []ast.Spec
+	if p.tok == token.LPAREN {
+		lparen = p.pos
+		p.next()
+		for iota := 0; p.tok != token.RPAREN && p.tok != token.EOF; iota++ {
+			list = append(list, f(p, p.leadComment, iota))
+		}
+		rparen = p.expect(token.RPAREN)
+		p.expectSemi()
+	} else {
+		list = append(list, f(p, nil, 0))
+	}
+
+	return &ast.GenDecl{doc, pos, keyword, lparen, list, rparen}
+}
+
+func (p *parser) parseReceiver(scope *ast.Scope) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Receiver"))
+	}
+
+	pos := p.pos
+	par := p.parseParameters(scope, false)
+
+	// must have exactly one receiver
+	if par.NumFields() != 1 {
+		p.errorExpected(pos, "exactly one receiver")
+		// TODO determine a better range for BadExpr below
+		par.List = []*ast.Field{&ast.Field{Type: &ast.BadExpr{pos, pos}}}
+		return par
+	}
+
+	// recv type must be of the form ["*"] identifier
+	recv := par.List[0]
+	base := deref(recv.Type)
+	if _, isIdent := base.(*ast.Ident); !isIdent {
+		p.errorExpected(base.Pos(), "(unqualified) identifier")
+		par.List = []*ast.Field{&ast.Field{Type: &ast.BadExpr{recv.Pos(), recv.End()}}}
+	}
+
+	return par
+}
+
+func (p *parser) parseFuncDecl() *ast.FuncDecl {
+	if p.trace {
+		defer un(trace(p, "FunctionDecl"))
+	}
+
+	doc := p.leadComment
+	pos := p.expect(token.FUNC)
+	scope := ast.NewScope(p.topScope) // function scope
+
+	var recv *ast.FieldList
+	if p.tok == token.LPAREN {
+		recv = p.parseReceiver(scope)
+	}
+
+	ident := p.parseIdent()
+
+	params, results := p.parseSignature(scope)
+
+	var body *ast.BlockStmt
+	if p.tok == token.LBRACE {
+		body = p.parseBody(scope)
+	}
+	p.expectSemi()
+
+	decl := &ast.FuncDecl{doc, recv, ident, &ast.FuncType{pos, params, results}, body}
+	if recv == nil {
+		// Go spec: The scope of an identifier denoting a constant, type,
+		// variable, or function (but not method) declared at top level
+		// (outside any function) is the package block.
+		//
+		// init() functions cannot be referred to and there may
+		// be more than one - don't put them in the pkgScope
+		if ident.Name != "init" {
+			p.declare(decl, nil, p.pkgScope, ast.Fun, ident)
+		}
+	}
+
+	return decl
+}
+
+func (p *parser) parseDecl() ast.Decl {
+	if p.trace {
+		defer un(trace(p, "Declaration"))
+	}
+
+	var f parseSpecFunction
+	switch p.tok {
+	case token.CONST:
+		f = parseConstSpec
+
+	case token.TYPE:
+		f = parseTypeSpec
+
+	case token.VAR:
+		f = parseVarSpec
+
+	case token.FUNC:
+		return p.parseFuncDecl()
+
+	default:
+		pos := p.pos
+		p.errorExpected(pos, "declaration")
+		p.next() // make progress
+		decl := &ast.BadDecl{pos, p.pos}
+		return decl
+	}
+
+	return p.parseGenDecl(p.tok, f)
+}
+
+func (p *parser) parseDeclList() (list []ast.Decl) {
+	if p.trace {
+		defer un(trace(p, "DeclList"))
+	}
+
+	for p.tok != token.EOF {
+		list = append(list, p.parseDecl())
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Source files
+
+func (p *parser) parseFile() *ast.File {
+	if p.trace {
+		defer un(trace(p, "File"))
+	}
+
+	// package clause
+	doc := p.leadComment
+	pos := p.expect(token.PACKAGE)
+	// Go spec: The package clause is not a declaration;
+	// the package name does not appear in any scope.
+	ident := p.parseIdent()
+	if ident.Name == "_" {
+		p.error(p.pos, "invalid package name _")
+	}
+	p.expectSemi()
+
+	var decls []ast.Decl
+
+	// Don't bother parsing the rest if we had errors already.
+	// Likely not a Go source file at all.
+
+	if p.ErrorCount() == 0 && p.mode&PackageClauseOnly == 0 {
+		// import decls
+		for p.tok == token.IMPORT {
+			decls = append(decls, p.parseGenDecl(token.IMPORT, parseImportSpec))
+		}
+
+		if p.mode&ImportsOnly == 0 {
+			// rest of package body
+			for p.tok != token.EOF {
+				decls = append(decls, p.parseDecl())
+			}
+		}
+	}
+
+	assert(p.topScope == p.pkgScope, "imbalanced scopes")
+
+	// resolve global identifiers within the same file
+	i := 0
+	for _, ident := range p.unresolved {
+		// i <= index for current ident
+		assert(ident.Obj == unresolved, "object already resolved")
+		ident.Obj = p.pkgScope.Lookup(ident.Name) // also removes unresolved sentinel
+		if ident.Obj == nil {
+			p.unresolved[i] = ident
+			i++
+		}
+	}
+
+	return &ast.File{doc, pos, ident, decls, p.pkgScope, p.imports, p.unresolved[0:i], p.comments}
+}
diff --git a/src/pkg/go/parser/parser_test.go b/src/pkg/go/parser/parser_test.go
new file mode 100644
index 000000000..39a78e515
--- /dev/null
+++ b/src/pkg/go/parser/parser_test.go
@@ -0,0 +1,130 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package parser
+
+import (
+	"go/token"
+	"os"
+	"testing"
+)
+
+var fset = token.NewFileSet()
+
+var illegalInputs = []interface{}{
+	nil,
+	3.14,
+	[]byte(nil),
+	"foo!",
+	`package p; func f() { if /* should have condition */ {} };`,
+	`package p; func f() { if ; /* should have condition */ {} };`,
+	`package p; func f() { if f(); /* should have condition */ {} };`,
+	`package p; const c; /* should have constant value */`,
+	`package p; func f() { if _ = range x; true {} };`,
+	`package p; func f() { switch _ = range x; true {} };`,
+	`package p; func f() { for _ = range x ; ; {} };`,
+	`package p; func f() { for ; ; _ = range x {} };`,
+	`package p; func f() { for ; _ = range x ; {} };`,
+	`package p; var a = [1]int; /* illegal expression */`,
+	`package p; var a = [...]int; /* illegal expression */`,
+	`package p; var a = struct{} /* illegal expression */`,
+	`package p; var a = func(); /* illegal expression */`,
+	`package p; var a = interface{} /* illegal expression */`,
+	`package p; var a = []int /* illegal expression */`,
+	`package p; var a = map[int]int /* illegal expression */`,
+	`package p; var a = chan int; /* illegal expression */`,
+	`package p; var a = []int{[]int}; /* illegal expression */`,
+	`package p; var a = ([]int); /* illegal expression */`,
+	`package p; var a = a[[]int:[]int]; /* illegal expression */`,
+	`package p; var a = <- chan int; /* illegal expression */`,
+	`package p; func f() { select { case _ <- chan int: } };`,
+}
+
+func TestParseIllegalInputs(t *testing.T) {
+	for _, src := range illegalInputs {
+		_, err := ParseFile(fset, "", src, 0)
+		if err == nil {
+			t.Errorf("ParseFile(%v) should have failed", src)
+		}
+	}
+}
+
+var validPrograms = []interface{}{
+	"package p\n",
+	`package p;`,
+	`package p; import "fmt"; func f() { fmt.Println("Hello, World!") };`,
+	`package p; func f() { if f(T{}) {} };`,
+	`package p; func f() { _ = (<-chan int)(x) };`,
+	`package p; func f() { _ = (<-chan <-chan int)(x) };`,
+	`package p; func f(func() func() func());`,
+	`package p; func f(...T);`,
+	`package p; func f(float, ...int);`,
+	`package p; func f(x int, a ...int) { f(0, a...); f(1, a...,) };`,
+	`package p; type T []int; var a []bool; func f() { if a[T{42}[0]] {} };`,
+	`package p; type T []int; func g(int) bool { return true }; func f() { if g(T{42}[0]) {} };`,
+	`package p; type T []int; func f() { for _ = range []int{T{42}[0]} {} };`,
+	`package p; var a = T{{1, 2}, {3, 4}}`,
+	`package p; func f() { select { case <- c: case c <- d: case c <- <- d: case <-c <- d: } };`,
+	`package p; func f() { select { case x := (<-c): } };`,
+	`package p; func f() { if ; true {} };`,
+	`package p; func f() { switch ; {} };`,
+	`package p; func f() { for _ = range "foo" + "bar" {} };`,
+}
+
+func TestParseValidPrograms(t *testing.T) {
+	for _, src := range validPrograms {
+		_, err := ParseFile(fset, "", src, 0)
+		if err != nil {
+			t.Errorf("ParseFile(%q): %v", src, err)
+		}
+	}
+}
+
+var validFiles = []string{
+	"parser.go",
+	"parser_test.go",
+}
+
+func TestParse3(t *testing.T) {
+	for _, filename := range validFiles {
+		_, err := ParseFile(fset, filename, nil, DeclarationErrors)
+		if err != nil {
+			t.Errorf("ParseFile(%s): %v", filename, err)
+		}
+	}
+}
+
+func nameFilter(filename string) bool {
+	switch filename {
+	case "parser.go":
+	case "interface.go":
+	case "parser_test.go":
+	default:
+		return false
+	}
+	return true
+}
+
+func dirFilter(f *os.FileInfo) bool { return nameFilter(f.Name) }
+
+func TestParse4(t *testing.T) {
+	path := "."
+	pkgs, err := ParseDir(fset, path, dirFilter, 0)
+	if err != nil {
+		t.Fatalf("ParseDir(%s): %v", path, err)
+	}
+	if len(pkgs) != 1 {
+		t.Errorf("incorrect number of packages: %d", len(pkgs))
+	}
+	pkg := pkgs["parser"]
+	if pkg == nil {
+		t.Errorf(`package "parser" not found`)
+		return
+	}
+	for filename := range pkg.Files {
+		if !nameFilter(filename) {
+			t.Errorf("unexpected package file: %s", filename)
+		}
+	}
+}
diff --git a/src/pkg/go/printer/Makefile b/src/pkg/go/printer/Makefile
new file mode 100644
index 000000000..6a71efc93
--- /dev/null
+++ b/src/pkg/go/printer/Makefile
@@ -0,0 +1,12 @@
+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../Make.inc
+
+TARG=go/printer
+GOFILES=\
+	printer.go\
+	nodes.go\
+
+include ../../../Make.pkg
diff --git a/src/pkg/go/printer/nodes.go b/src/pkg/go/printer/nodes.go
new file mode 100644
index 000000000..9cd975ec1
--- /dev/null
+++ b/src/pkg/go/printer/nodes.go
@@ -0,0 +1,1510 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements printing of AST nodes; specifically
+// expressions, statements, declarations, and files. It uses
+// the print functionality implemented in printer.go.
+
+package printer
+
+import (
+	"bytes"
+	"go/ast"
+	"go/token"
+)
+
+// Other formatting issues:
+// - better comment formatting for /*-style comments at the end of a line (e.g. a declaration)
+//   when the comment spans multiple lines; if such a comment is just two lines, formatting is
+//   not idempotent
+// - formatting of expression lists
+// - should use blank instead of tab to separate one-line function bodies from
+//   the function header unless there is a group of consecutive one-liners
+
+// ----------------------------------------------------------------------------
+// Common AST nodes.
+
+// Print as many newlines as necessary (but at least min newlines) to get to
+// the current line. ws is printed before the first line break. If newSection
+// is set, the first line break is printed as formfeed. Returns true if any
+// line break was printed; returns false otherwise.
+//
+// TODO(gri): linebreak may add too many lines if the next statement at "line"
+//            is preceded by comments because the computation of n assumes
+//            the current position before the comment and the target position
+//            after the comment. Thus, after interspersing such comments, the
+//            space taken up by them is not considered to reduce the number of
+//            linebreaks. At the moment there is no easy way to know about
+//            future (not yet interspersed) comments in this function.
+//
+func (p *printer) linebreak(line, min int, ws whiteSpace, newSection bool) (printedBreak bool) {
+	n := p.nlines(line-p.pos.Line, min)
+	if n > 0 {
+		p.print(ws)
+		if newSection {
+			p.print(formfeed)
+			n--
+		}
+		for ; n > 0; n-- {
+			p.print(newline)
+		}
+		printedBreak = true
+	}
+	return
+}
+
+// setComment sets g as the next comment if g != nil and if node comments
+// are enabled - this mode is used when printing source code fragments such
+// as exports only. It assumes that there are no other pending comments to
+// intersperse.
+func (p *printer) setComment(g *ast.CommentGroup) {
+	if g == nil || !p.useNodeComments {
+		return
+	}
+	if p.comments == nil {
+		// initialize p.comments lazily
+		p.comments = make([]*ast.CommentGroup, 1)
+	} else if p.cindex < len(p.comments) {
+		// for some reason there are pending comments; this
+		// should never happen - handle gracefully and flush
+		// all comments up to g, ignore anything after that
+		p.flush(p.fset.Position(g.List[0].Pos()), token.ILLEGAL)
+	}
+	p.comments[0] = g
+	p.cindex = 0
+}
+
+type exprListMode uint
+
+const (
+	blankStart exprListMode = 1 << iota // print a blank before a non-empty list
+	blankEnd                            // print a blank after a non-empty list
+	commaSep                            // elements are separated by commas
+	commaTerm                           // list is optionally terminated by a comma
+	noIndent                            // no extra indentation in multi-line lists
+	periodSep                           // elements are separated by periods
+)
+
+// Sets multiLine to true if the identifier list spans multiple lines.
+// If indent is set, a multi-line identifier list is indented after the
+// first linebreak encountered.
+func (p *printer) identList(list []*ast.Ident, indent bool, multiLine *bool) {
+	// convert into an expression list so we can re-use exprList formatting
+	xlist := make([]ast.Expr, len(list))
+	for i, x := range list {
+		xlist[i] = x
+	}
+	mode := commaSep
+	if !indent {
+		mode |= noIndent
+	}
+	p.exprList(token.NoPos, xlist, 1, mode, multiLine, token.NoPos)
+}
+
+// Print a list of expressions. If the list spans multiple
+// source lines, the original line breaks are respected between
+// expressions. Sets multiLine to true if the list spans multiple
+// lines.
+//
+// TODO(gri) Consider rewriting this to be independent of []ast.Expr
+//           so that we can use the algorithm for any kind of list
+//           (e.g., pass list via a channel over which to range).
+func (p *printer) exprList(prev0 token.Pos, list []ast.Expr, depth int, mode exprListMode, multiLine *bool, next0 token.Pos) {
+	if len(list) == 0 {
+		return
+	}
+
+	if mode&blankStart != 0 {
+		p.print(blank)
+	}
+
+	prev := p.fset.Position(prev0)
+	next := p.fset.Position(next0)
+	line := p.fset.Position(list[0].Pos()).Line
+	endLine := p.fset.Position(list[len(list)-1].End()).Line
+
+	if prev.IsValid() && prev.Line == line && line == endLine {
+		// all list entries on a single line
+		for i, x := range list {
+			if i > 0 {
+				if mode&commaSep != 0 {
+					p.print(token.COMMA)
+				}
+				p.print(blank)
+			}
+			p.expr0(x, depth, multiLine)
+		}
+		if mode&blankEnd != 0 {
+			p.print(blank)
+		}
+		return
+	}
+
+	// list entries span multiple lines;
+	// use source code positions to guide line breaks
+
+	// don't add extra indentation if noIndent is set;
+	// i.e., pretend that the first line is already indented
+	ws := ignore
+	if mode&noIndent == 0 {
+		ws = indent
+	}
+
+	// the first linebreak is always a formfeed since this section must not
+	// depend on any previous formatting
+	prevBreak := -1 // index of last expression that was followed by a linebreak
+	if prev.IsValid() && prev.Line < line && p.linebreak(line, 0, ws, true) {
+		ws = ignore
+		*multiLine = true
+		prevBreak = 0
+	}
+
+	// initialize expression/key size: a zero value indicates expr/key doesn't fit on a single line
+	size := 0
+
+	// print all list elements
+	for i, x := range list {
+		prevLine := line
+		line = p.fset.Position(x.Pos()).Line
+
+		// determine if the next linebreak, if any, needs to use formfeed:
+		// in general, use the entire node size to make the decision; for
+		// key:value expressions, use the key size
+		// TODO(gri) for a better result, should probably incorporate both
+		//           the key and the node size into the decision process
+		useFF := true
+
+		// determine element size: all bets are off if we don't have
+		// position information for the previous and next token (likely
+		// generated code - simply ignore the size in this case by setting
+		// it to 0)
+		prevSize := size
+		const infinity = 1e6 // larger than any source line
+		size = p.nodeSize(x, infinity)
+		pair, isPair := x.(*ast.KeyValueExpr)
+		if size <= infinity && prev.IsValid() && next.IsValid() {
+			// x fits on a single line
+			if isPair {
+				size = p.nodeSize(pair.Key, infinity) // size <= infinity
+			}
+		} else {
+			// size too large or we don't have good layout information
+			size = 0
+		}
+
+		// if the previous line and the current line had single-
+		// line-expressions and the key sizes are small or the
+		// the ratio between the key sizes does not exceed a
+		// threshold, align columns and do not use formfeed
+		if prevSize > 0 && size > 0 {
+			const smallSize = 20
+			if prevSize <= smallSize && size <= smallSize {
+				useFF = false
+			} else {
+				const r = 4 // threshold
+				ratio := float64(size) / float64(prevSize)
+				useFF = ratio <= 1/r || r <= ratio
+			}
+		}
+
+		if i > 0 {
+			switch {
+			case mode&commaSep != 0:
+				p.print(token.COMMA)
+			case mode&periodSep != 0:
+				p.print(token.PERIOD)
+			}
+			needsBlank := mode&periodSep == 0 // period-separated list elements don't need a blank
+			if prevLine < line && prevLine > 0 && line > 0 {
+				// lines are broken using newlines so comments remain aligned
+				// unless forceFF is set or there are multiple expressions on
+				// the same line in which case formfeed is used
+				if p.linebreak(line, 0, ws, useFF || prevBreak+1 < i) {
+					ws = ignore
+					*multiLine = true
+					prevBreak = i
+					needsBlank = false // we got a line break instead
+				}
+			}
+			if needsBlank {
+				p.print(blank)
+			}
+		}
+
+		if isPair && size > 0 && len(list) > 1 {
+			// we have a key:value expression that fits onto one line and
+			// is in a list with more then one entry: use a column for the
+			// key such that consecutive entries can align if possible
+			p.expr(pair.Key, multiLine)
+			p.print(pair.Colon, token.COLON, vtab)
+			p.expr(pair.Value, multiLine)
+		} else {
+			p.expr0(x, depth, multiLine)
+		}
+	}
+
+	if mode&commaTerm != 0 && next.IsValid() && p.pos.Line < next.Line {
+		// print a terminating comma if the next token is on a new line
+		p.print(token.COMMA)
+		if ws == ignore && mode&noIndent == 0 {
+			// unindent if we indented
+			p.print(unindent)
+		}
+		p.print(formfeed) // terminating comma needs a line break to look good
+		return
+	}
+
+	if mode&blankEnd != 0 {
+		p.print(blank)
+	}
+
+	if ws == ignore && mode&noIndent == 0 {
+		// unindent if we indented
+		p.print(unindent)
+	}
+}
+
+// Sets multiLine to true if the the parameter list spans multiple lines.
+func (p *printer) parameters(fields *ast.FieldList, multiLine *bool) {
+	p.print(fields.Opening, token.LPAREN)
+	if len(fields.List) > 0 {
+		var prevLine, line int
+		for i, par := range fields.List {
+			if i > 0 {
+				p.print(token.COMMA)
+				if len(par.Names) > 0 {
+					line = p.fset.Position(par.Names[0].Pos()).Line
+				} else {
+					line = p.fset.Position(par.Type.Pos()).Line
+				}
+				if 0 < prevLine && prevLine < line && p.linebreak(line, 0, ignore, true) {
+					*multiLine = true
+				} else {
+					p.print(blank)
+				}
+			}
+			if len(par.Names) > 0 {
+				p.identList(par.Names, false, multiLine)
+				p.print(blank)
+			}
+			p.expr(par.Type, multiLine)
+			prevLine = p.fset.Position(par.Type.Pos()).Line
+		}
+	}
+	p.print(fields.Closing, token.RPAREN)
+}
+
+// Sets multiLine to true if the signature spans multiple lines.
+func (p *printer) signature(params, result *ast.FieldList, multiLine *bool) {
+	p.parameters(params, multiLine)
+	n := result.NumFields()
+	if n > 0 {
+		p.print(blank)
+		if n == 1 && result.List[0].Names == nil {
+			// single anonymous result; no ()'s
+			p.expr(result.List[0].Type, multiLine)
+			return
+		}
+		p.parameters(result, multiLine)
+	}
+}
+
+func identListSize(list []*ast.Ident, maxSize int) (size int) {
+	for i, x := range list {
+		if i > 0 {
+			size += 2 // ", "
+		}
+		size += len(x.Name)
+		if size >= maxSize {
+			break
+		}
+	}
+	return
+}
+
+func (p *printer) isOneLineFieldList(list []*ast.Field) bool {
+	if len(list) != 1 {
+		return false // allow only one field
+	}
+	f := list[0]
+	if f.Tag != nil || f.Comment != nil {
+		return false // don't allow tags or comments
+	}
+	// only name(s) and type
+	const maxSize = 30 // adjust as appropriate, this is an approximate value
+	namesSize := identListSize(f.Names, maxSize)
+	if namesSize > 0 {
+		namesSize = 1 // blank between names and types
+	}
+	typeSize := p.nodeSize(f.Type, maxSize)
+	return namesSize+typeSize <= maxSize
+}
+
+func (p *printer) setLineComment(text string) {
+	p.setComment(&ast.CommentGroup{[]*ast.Comment{&ast.Comment{token.NoPos, text}}})
+}
+
+func (p *printer) fieldList(fields *ast.FieldList, isStruct, isIncomplete bool) {
+	lbrace := fields.Opening
+	list := fields.List
+	rbrace := fields.Closing
+	srcIsOneLine := lbrace.IsValid() && rbrace.IsValid() && p.fset.Position(lbrace).Line == p.fset.Position(rbrace).Line
+
+	if !isIncomplete && !p.commentBefore(p.fset.Position(rbrace)) && srcIsOneLine {
+		// possibly a one-line struct/interface
+		if len(list) == 0 {
+			// no blank between keyword and {} in this case
+			p.print(lbrace, token.LBRACE, rbrace, token.RBRACE)
+			return
+		} else if isStruct && p.isOneLineFieldList(list) { // for now ignore interfaces
+			// small enough - print on one line
+			// (don't use identList and ignore source line breaks)
+			p.print(lbrace, token.LBRACE, blank)
+			f := list[0]
+			for i, x := range f.Names {
+				if i > 0 {
+					p.print(token.COMMA, blank)
+				}
+				p.expr(x, ignoreMultiLine)
+			}
+			if len(f.Names) > 0 {
+				p.print(blank)
+			}
+			p.expr(f.Type, ignoreMultiLine)
+			p.print(blank, rbrace, token.RBRACE)
+			return
+		}
+	}
+
+	// at least one entry or incomplete
+	p.print(blank, lbrace, token.LBRACE, indent, formfeed)
+	if isStruct {
+
+		sep := vtab
+		if len(list) == 1 {
+			sep = blank
+		}
+		var ml bool
+		for i, f := range list {
+			if i > 0 {
+				p.linebreak(p.fset.Position(f.Pos()).Line, 1, ignore, ml)
+			}
+			ml = false
+			extraTabs := 0
+			p.setComment(f.Doc)
+			if len(f.Names) > 0 {
+				// named fields
+				p.identList(f.Names, false, &ml)
+				p.print(sep)
+				p.expr(f.Type, &ml)
+				extraTabs = 1
+			} else {
+				// anonymous field
+				p.expr(f.Type, &ml)
+				extraTabs = 2
+			}
+			if f.Tag != nil {
+				if len(f.Names) > 0 && sep == vtab {
+					p.print(sep)
+				}
+				p.print(sep)
+				p.expr(f.Tag, &ml)
+				extraTabs = 0
+			}
+			if f.Comment != nil {
+				for ; extraTabs > 0; extraTabs-- {
+					p.print(sep)
+				}
+				p.setComment(f.Comment)
+			}
+		}
+		if isIncomplete {
+			if len(list) > 0 {
+				p.print(formfeed)
+			}
+			p.flush(p.fset.Position(rbrace), token.RBRACE) // make sure we don't lose the last line comment
+			p.setLineComment("// contains filtered or unexported fields")
+		}
+
+	} else { // interface
+
+		var ml bool
+		for i, f := range list {
+			if i > 0 {
+				p.linebreak(p.fset.Position(f.Pos()).Line, 1, ignore, ml)
+			}
+			ml = false
+			p.setComment(f.Doc)
+			if ftyp, isFtyp := f.Type.(*ast.FuncType); isFtyp {
+				// method
+				p.expr(f.Names[0], &ml)
+				p.signature(ftyp.Params, ftyp.Results, &ml)
+			} else {
+				// embedded interface
+				p.expr(f.Type, &ml)
+			}
+			p.setComment(f.Comment)
+		}
+		if isIncomplete {
+			if len(list) > 0 {
+				p.print(formfeed)
+			}
+			p.flush(p.fset.Position(rbrace), token.RBRACE) // make sure we don't lose the last line comment
+			p.setLineComment("// contains filtered or unexported methods")
+		}
+
+	}
+	p.print(unindent, formfeed, rbrace, token.RBRACE)
+}
+
+// ----------------------------------------------------------------------------
+// Expressions
+
+func walkBinary(e *ast.BinaryExpr) (has4, has5 bool, maxProblem int) {
+	switch e.Op.Precedence() {
+	case 4:
+		has4 = true
+	case 5:
+		has5 = true
+	}
+
+	switch l := e.X.(type) {
+	case *ast.BinaryExpr:
+		if l.Op.Precedence() < e.Op.Precedence() {
+			// parens will be inserted.
+			// pretend this is an *ast.ParenExpr and do nothing.
+			break
+		}
+		h4, h5, mp := walkBinary(l)
+		has4 = has4 || h4
+		has5 = has5 || h5
+		if maxProblem < mp {
+			maxProblem = mp
+		}
+	}
+
+	switch r := e.Y.(type) {
+	case *ast.BinaryExpr:
+		if r.Op.Precedence() <= e.Op.Precedence() {
+			// parens will be inserted.
+			// pretend this is an *ast.ParenExpr and do nothing.
+			break
+		}
+		h4, h5, mp := walkBinary(r)
+		has4 = has4 || h4
+		has5 = has5 || h5
+		if maxProblem < mp {
+			maxProblem = mp
+		}
+
+	case *ast.StarExpr:
+		if e.Op == token.QUO { // `*/`
+			maxProblem = 5
+		}
+
+	case *ast.UnaryExpr:
+		switch e.Op.String() + r.Op.String() {
+		case "/*", "&&", "&^":
+			maxProblem = 5
+		case "++", "--":
+			if maxProblem < 4 {
+				maxProblem = 4
+			}
+		}
+	}
+	return
+}
+
+func cutoff(e *ast.BinaryExpr, depth int) int {
+	has4, has5, maxProblem := walkBinary(e)
+	if maxProblem > 0 {
+		return maxProblem + 1
+	}
+	if has4 && has5 {
+		if depth == 1 {
+			return 5
+		}
+		return 4
+	}
+	if depth == 1 {
+		return 6
+	}
+	return 4
+}
+
+func diffPrec(expr ast.Expr, prec int) int {
+	x, ok := expr.(*ast.BinaryExpr)
+	if !ok || prec != x.Op.Precedence() {
+		return 1
+	}
+	return 0
+}
+
+func reduceDepth(depth int) int {
+	depth--
+	if depth < 1 {
+		depth = 1
+	}
+	return depth
+}
+
+// Format the binary expression: decide the cutoff and then format.
+// Let's call depth == 1 Normal mode, and depth > 1 Compact mode.
+// (Algorithm suggestion by Russ Cox.)
+//
+// The precedences are:
+//	5             *  /  %  <<  >>  &  &^
+//	4             +  -  |  ^
+//	3             ==  !=  <  <=  >  >=
+//	2             &&
+//	1             ||
+//
+// The only decision is whether there will be spaces around levels 4 and 5.
+// There are never spaces at level 6 (unary), and always spaces at levels 3 and below.
+//
+// To choose the cutoff, look at the whole expression but excluding primary
+// expressions (function calls, parenthesized exprs), and apply these rules:
+//
+//	1) If there is a binary operator with a right side unary operand
+//	   that would clash without a space, the cutoff must be (in order):
+//
+//		/*	6
+//		&&	6
+//		&^	6
+//		++	5
+//		--	5
+//
+//         (Comparison operators always have spaces around them.)
+//
+//	2) If there is a mix of level 5 and level 4 operators, then the cutoff
+//	   is 5 (use spaces to distinguish precedence) in Normal mode
+//	   and 4 (never use spaces) in Compact mode.
+//
+//	3) If there are no level 4 operators or no level 5 operators, then the
+//	   cutoff is 6 (always use spaces) in Normal mode
+//	   and 4 (never use spaces) in Compact mode.
+//
+// Sets multiLine to true if the binary expression spans multiple lines.
+func (p *printer) binaryExpr(x *ast.BinaryExpr, prec1, cutoff, depth int, multiLine *bool) {
+	prec := x.Op.Precedence()
+	if prec < prec1 {
+		// parenthesis needed
+		// Note: The parser inserts an ast.ParenExpr node; thus this case
+		//       can only occur if the AST is created in a different way.
+		p.print(token.LPAREN)
+		p.expr0(x, reduceDepth(depth), multiLine) // parentheses undo one level of depth
+		p.print(token.RPAREN)
+		return
+	}
+
+	printBlank := prec < cutoff
+
+	ws := indent
+	p.expr1(x.X, prec, depth+diffPrec(x.X, prec), multiLine)
+	if printBlank {
+		p.print(blank)
+	}
+	xline := p.pos.Line // before the operator (it may be on the next line!)
+	yline := p.fset.Position(x.Y.Pos()).Line
+	p.print(x.OpPos, x.Op)
+	if xline != yline && xline > 0 && yline > 0 {
+		// at least one line break, but respect an extra empty line
+		// in the source
+		if p.linebreak(yline, 1, ws, true) {
+			ws = ignore
+			*multiLine = true
+			printBlank = false // no blank after line break
+		}
+	}
+	if printBlank {
+		p.print(blank)
+	}
+	p.expr1(x.Y, prec+1, depth+1, multiLine)
+	if ws == ignore {
+		p.print(unindent)
+	}
+}
+
+func isBinary(expr ast.Expr) bool {
+	_, ok := expr.(*ast.BinaryExpr)
+	return ok
+}
+
+// If the expression contains one or more selector expressions, splits it into
+// two expressions at the rightmost period. Writes entire expr to suffix when
+// selector isn't found. Rewrites AST nodes for calls, index expressions and
+// type assertions, all of which may be found in selector chains, to make them
+// parts of the chain.
+func splitSelector(expr ast.Expr) (body, suffix ast.Expr) {
+	switch x := expr.(type) {
+	case *ast.SelectorExpr:
+		body, suffix = x.X, x.Sel
+		return
+	case *ast.CallExpr:
+		body, suffix = splitSelector(x.Fun)
+		if body != nil {
+			suffix = &ast.CallExpr{suffix, x.Lparen, x.Args, x.Ellipsis, x.Rparen}
+			return
+		}
+	case *ast.IndexExpr:
+		body, suffix = splitSelector(x.X)
+		if body != nil {
+			suffix = &ast.IndexExpr{suffix, x.Lbrack, x.Index, x.Rbrack}
+			return
+		}
+	case *ast.SliceExpr:
+		body, suffix = splitSelector(x.X)
+		if body != nil {
+			suffix = &ast.SliceExpr{suffix, x.Lbrack, x.Low, x.High, x.Rbrack}
+			return
+		}
+	case *ast.TypeAssertExpr:
+		body, suffix = splitSelector(x.X)
+		if body != nil {
+			suffix = &ast.TypeAssertExpr{suffix, x.Type}
+			return
+		}
+	}
+	suffix = expr
+	return
+}
+
+// Convert an expression into an expression list split at the periods of
+// selector expressions.
+func selectorExprList(expr ast.Expr) (list []ast.Expr) {
+	// split expression
+	for expr != nil {
+		var suffix ast.Expr
+		expr, suffix = splitSelector(expr)
+		list = append(list, suffix)
+	}
+
+	// reverse list
+	for i, j := 0, len(list)-1; i < j; i, j = i+1, j-1 {
+		list[i], list[j] = list[j], list[i]
+	}
+
+	return
+}
+
+// Sets multiLine to true if the expression spans multiple lines.
+func (p *printer) expr1(expr ast.Expr, prec1, depth int, multiLine *bool) {
+	p.print(expr.Pos())
+
+	switch x := expr.(type) {
+	case *ast.BadExpr:
+		p.print("BadExpr")
+
+	case *ast.Ident:
+		p.print(x)
+
+	case *ast.BinaryExpr:
+		if depth < 1 {
+			p.internalError("depth < 1:", depth)
+			depth = 1
+		}
+		p.binaryExpr(x, prec1, cutoff(x, depth), depth, multiLine)
+
+	case *ast.KeyValueExpr:
+		p.expr(x.Key, multiLine)
+		p.print(x.Colon, token.COLON, blank)
+		p.expr(x.Value, multiLine)
+
+	case *ast.StarExpr:
+		const prec = token.UnaryPrec
+		if prec < prec1 {
+			// parenthesis needed
+			p.print(token.LPAREN)
+			p.print(token.MUL)
+			p.expr(x.X, multiLine)
+			p.print(token.RPAREN)
+		} else {
+			// no parenthesis needed
+			p.print(token.MUL)
+			p.expr(x.X, multiLine)
+		}
+
+	case *ast.UnaryExpr:
+		const prec = token.UnaryPrec
+		if prec < prec1 {
+			// parenthesis needed
+			p.print(token.LPAREN)
+			p.expr(x, multiLine)
+			p.print(token.RPAREN)
+		} else {
+			// no parenthesis needed
+			p.print(x.Op)
+			if x.Op == token.RANGE {
+				// TODO(gri) Remove this code if it cannot be reached.
+				p.print(blank)
+			}
+			p.expr1(x.X, prec, depth, multiLine)
+		}
+
+	case *ast.BasicLit:
+		p.print(x)
+
+	case *ast.FuncLit:
+		p.expr(x.Type, multiLine)
+		p.funcBody(x.Body, p.distance(x.Type.Pos(), p.pos), true, multiLine)
+
+	case *ast.ParenExpr:
+		if _, hasParens := x.X.(*ast.ParenExpr); hasParens {
+			// don't print parentheses around an already parenthesized expression
+			// TODO(gri) consider making this more general and incorporate precedence levels
+			p.expr0(x.X, reduceDepth(depth), multiLine) // parentheses undo one level of depth
+		} else {
+			p.print(token.LPAREN)
+			p.expr0(x.X, reduceDepth(depth), multiLine) // parentheses undo one level of depth
+			p.print(x.Rparen, token.RPAREN)
+		}
+
+	case *ast.SelectorExpr:
+		parts := selectorExprList(expr)
+		p.exprList(token.NoPos, parts, depth, periodSep, multiLine, token.NoPos)
+
+	case *ast.TypeAssertExpr:
+		p.expr1(x.X, token.HighestPrec, depth, multiLine)
+		p.print(token.PERIOD, token.LPAREN)
+		if x.Type != nil {
+			p.expr(x.Type, multiLine)
+		} else {
+			p.print(token.TYPE)
+		}
+		p.print(token.RPAREN)
+
+	case *ast.IndexExpr:
+		// TODO(gri): should treat[] like parentheses and undo one level of depth
+		p.expr1(x.X, token.HighestPrec, 1, multiLine)
+		p.print(x.Lbrack, token.LBRACK)
+		p.expr0(x.Index, depth+1, multiLine)
+		p.print(x.Rbrack, token.RBRACK)
+
+	case *ast.SliceExpr:
+		// TODO(gri): should treat[] like parentheses and undo one level of depth
+		p.expr1(x.X, token.HighestPrec, 1, multiLine)
+		p.print(x.Lbrack, token.LBRACK)
+		if x.Low != nil {
+			p.expr0(x.Low, depth+1, multiLine)
+		}
+		// blanks around ":" if both sides exist and either side is a binary expression
+		if depth <= 1 && x.Low != nil && x.High != nil && (isBinary(x.Low) || isBinary(x.High)) {
+			p.print(blank, token.COLON, blank)
+		} else {
+			p.print(token.COLON)
+		}
+		if x.High != nil {
+			p.expr0(x.High, depth+1, multiLine)
+		}
+		p.print(x.Rbrack, token.RBRACK)
+
+	case *ast.CallExpr:
+		if len(x.Args) > 1 {
+			depth++
+		}
+		p.expr1(x.Fun, token.HighestPrec, depth, multiLine)
+		p.print(x.Lparen, token.LPAREN)
+		p.exprList(x.Lparen, x.Args, depth, commaSep|commaTerm, multiLine, x.Rparen)
+		if x.Ellipsis.IsValid() {
+			p.print(x.Ellipsis, token.ELLIPSIS)
+		}
+		p.print(x.Rparen, token.RPAREN)
+
+	case *ast.CompositeLit:
+		// composite literal elements that are composite literals themselves may have the type omitted
+		if x.Type != nil {
+			p.expr1(x.Type, token.HighestPrec, depth, multiLine)
+		}
+		p.print(x.Lbrace, token.LBRACE)
+		p.exprList(x.Lbrace, x.Elts, 1, commaSep|commaTerm, multiLine, x.Rbrace)
+		// do not insert extra line breaks because of comments before
+		// the closing '}' as it might break the code if there is no
+		// trailing ','
+		p.print(noExtraLinebreak, x.Rbrace, token.RBRACE, noExtraLinebreak)
+
+	case *ast.Ellipsis:
+		p.print(token.ELLIPSIS)
+		if x.Elt != nil {
+			p.expr(x.Elt, multiLine)
+		}
+
+	case *ast.ArrayType:
+		p.print(token.LBRACK)
+		if x.Len != nil {
+			p.expr(x.Len, multiLine)
+		}
+		p.print(token.RBRACK)
+		p.expr(x.Elt, multiLine)
+
+	case *ast.StructType:
+		p.print(token.STRUCT)
+		p.fieldList(x.Fields, true, x.Incomplete)
+
+	case *ast.FuncType:
+		p.print(token.FUNC)
+		p.signature(x.Params, x.Results, multiLine)
+
+	case *ast.InterfaceType:
+		p.print(token.INTERFACE)
+		p.fieldList(x.Methods, false, x.Incomplete)
+
+	case *ast.MapType:
+		p.print(token.MAP, token.LBRACK)
+		p.expr(x.Key, multiLine)
+		p.print(token.RBRACK)
+		p.expr(x.Value, multiLine)
+
+	case *ast.ChanType:
+		switch x.Dir {
+		case ast.SEND | ast.RECV:
+			p.print(token.CHAN)
+		case ast.RECV:
+			p.print(token.ARROW, token.CHAN)
+		case ast.SEND:
+			p.print(token.CHAN, token.ARROW)
+		}
+		p.print(blank)
+		p.expr(x.Value, multiLine)
+
+	default:
+		panic("unreachable")
+	}
+
+	return
+}
+
+func (p *printer) expr0(x ast.Expr, depth int, multiLine *bool) {
+	p.expr1(x, token.LowestPrec, depth, multiLine)
+}
+
+// Sets multiLine to true if the expression spans multiple lines.
+func (p *printer) expr(x ast.Expr, multiLine *bool) {
+	const depth = 1
+	p.expr1(x, token.LowestPrec, depth, multiLine)
+}
+
+// ----------------------------------------------------------------------------
+// Statements
+
+// Print the statement list indented, but without a newline after the last statement.
+// Extra line breaks between statements in the source are respected but at most one
+// empty line is printed between statements.
+func (p *printer) stmtList(list []ast.Stmt, _indent int, nextIsRBrace bool) {
+	// TODO(gri): fix _indent code
+	if _indent > 0 {
+		p.print(indent)
+	}
+	var multiLine bool
+	for i, s := range list {
+		// _indent == 0 only for lists of switch/select case clauses;
+		// in those cases each clause is a new section
+		p.linebreak(p.fset.Position(s.Pos()).Line, 1, ignore, i == 0 || _indent == 0 || multiLine)
+		multiLine = false
+		p.stmt(s, nextIsRBrace && i == len(list)-1, &multiLine)
+	}
+	if _indent > 0 {
+		p.print(unindent)
+	}
+}
+
+// block prints an *ast.BlockStmt; it always spans at least two lines.
+func (p *printer) block(s *ast.BlockStmt, indent int) {
+	p.print(s.Pos(), token.LBRACE)
+	p.stmtList(s.List, indent, true)
+	p.linebreak(p.fset.Position(s.Rbrace).Line, 1, ignore, true)
+	p.print(s.Rbrace, token.RBRACE)
+}
+
+func isTypeName(x ast.Expr) bool {
+	switch t := x.(type) {
+	case *ast.Ident:
+		return true
+	case *ast.SelectorExpr:
+		return isTypeName(t.X)
+	}
+	return false
+}
+
+func stripParens(x ast.Expr) ast.Expr {
+	if px, strip := x.(*ast.ParenExpr); strip {
+		// parentheses must not be stripped if there are any
+		// unparenthesized composite literals starting with
+		// a type name
+		ast.Inspect(px.X, func(node ast.Node) bool {
+			switch x := node.(type) {
+			case *ast.ParenExpr:
+				// parentheses protect enclosed composite literals
+				return false
+			case *ast.CompositeLit:
+				if isTypeName(x.Type) {
+					strip = false // do not strip parentheses
+				}
+				return false
+			}
+			// in all other cases, keep inspecting
+			return true
+		})
+		if strip {
+			return stripParens(px.X)
+		}
+	}
+	return x
+}
+
+func (p *printer) controlClause(isForStmt bool, init ast.Stmt, expr ast.Expr, post ast.Stmt) {
+	p.print(blank)
+	needsBlank := false
+	if init == nil && post == nil {
+		// no semicolons required
+		if expr != nil {
+			p.expr(stripParens(expr), ignoreMultiLine)
+			needsBlank = true
+		}
+	} else {
+		// all semicolons required
+		// (they are not separators, print them explicitly)
+		if init != nil {
+			p.stmt(init, false, ignoreMultiLine)
+		}
+		p.print(token.SEMICOLON, blank)
+		if expr != nil {
+			p.expr(stripParens(expr), ignoreMultiLine)
+			needsBlank = true
+		}
+		if isForStmt {
+			p.print(token.SEMICOLON, blank)
+			needsBlank = false
+			if post != nil {
+				p.stmt(post, false, ignoreMultiLine)
+				needsBlank = true
+			}
+		}
+	}
+	if needsBlank {
+		p.print(blank)
+	}
+}
+
+// Sets multiLine to true if the statements spans multiple lines.
+func (p *printer) stmt(stmt ast.Stmt, nextIsRBrace bool, multiLine *bool) {
+	p.print(stmt.Pos())
+
+	switch s := stmt.(type) {
+	case *ast.BadStmt:
+		p.print("BadStmt")
+
+	case *ast.DeclStmt:
+		p.decl(s.Decl, multiLine)
+
+	case *ast.EmptyStmt:
+		// nothing to do
+
+	case *ast.LabeledStmt:
+		// a "correcting" unindent immediately following a line break
+		// is applied before the line break if there is no comment
+		// between (see writeWhitespace)
+		p.print(unindent)
+		p.expr(s.Label, multiLine)
+		p.print(s.Colon, token.COLON, indent)
+		if e, isEmpty := s.Stmt.(*ast.EmptyStmt); isEmpty {
+			if !nextIsRBrace {
+				p.print(newline, e.Pos(), token.SEMICOLON)
+				break
+			}
+		} else {
+			p.linebreak(p.fset.Position(s.Stmt.Pos()).Line, 1, ignore, true)
+		}
+		p.stmt(s.Stmt, nextIsRBrace, multiLine)
+
+	case *ast.ExprStmt:
+		const depth = 1
+		p.expr0(s.X, depth, multiLine)
+
+	case *ast.SendStmt:
+		const depth = 1
+		p.expr0(s.Chan, depth, multiLine)
+		p.print(blank, s.Arrow, token.ARROW, blank)
+		p.expr0(s.Value, depth, multiLine)
+
+	case *ast.IncDecStmt:
+		const depth = 1
+		p.expr0(s.X, depth+1, multiLine)
+		p.print(s.TokPos, s.Tok)
+
+	case *ast.AssignStmt:
+		var depth = 1
+		if len(s.Lhs) > 1 && len(s.Rhs) > 1 {
+			depth++
+		}
+		p.exprList(s.Pos(), s.Lhs, depth, commaSep, multiLine, s.TokPos)
+		p.print(blank, s.TokPos, s.Tok)
+		p.exprList(s.TokPos, s.Rhs, depth, blankStart|commaSep, multiLine, token.NoPos)
+
+	case *ast.GoStmt:
+		p.print(token.GO, blank)
+		p.expr(s.Call, multiLine)
+
+	case *ast.DeferStmt:
+		p.print(token.DEFER, blank)
+		p.expr(s.Call, multiLine)
+
+	case *ast.ReturnStmt:
+		p.print(token.RETURN)
+		if s.Results != nil {
+			p.exprList(s.Pos(), s.Results, 1, blankStart|commaSep, multiLine, token.NoPos)
+		}
+
+	case *ast.BranchStmt:
+		p.print(s.Tok)
+		if s.Label != nil {
+			p.print(blank)
+			p.expr(s.Label, multiLine)
+		}
+
+	case *ast.BlockStmt:
+		p.block(s, 1)
+		*multiLine = true
+
+	case *ast.IfStmt:
+		p.print(token.IF)
+		p.controlClause(false, s.Init, s.Cond, nil)
+		p.block(s.Body, 1)
+		*multiLine = true
+		if s.Else != nil {
+			p.print(blank, token.ELSE, blank)
+			switch s.Else.(type) {
+			case *ast.BlockStmt, *ast.IfStmt:
+				p.stmt(s.Else, nextIsRBrace, ignoreMultiLine)
+			default:
+				p.print(token.LBRACE, indent, formfeed)
+				p.stmt(s.Else, true, ignoreMultiLine)
+				p.print(unindent, formfeed, token.RBRACE)
+			}
+		}
+
+	case *ast.CaseClause:
+		if s.List != nil {
+			p.print(token.CASE)
+			p.exprList(s.Pos(), s.List, 1, blankStart|commaSep, multiLine, s.Colon)
+		} else {
+			p.print(token.DEFAULT)
+		}
+		p.print(s.Colon, token.COLON)
+		p.stmtList(s.Body, 1, nextIsRBrace)
+
+	case *ast.SwitchStmt:
+		p.print(token.SWITCH)
+		p.controlClause(false, s.Init, s.Tag, nil)
+		p.block(s.Body, 0)
+		*multiLine = true
+
+	case *ast.TypeSwitchStmt:
+		p.print(token.SWITCH)
+		if s.Init != nil {
+			p.print(blank)
+			p.stmt(s.Init, false, ignoreMultiLine)
+			p.print(token.SEMICOLON)
+		}
+		p.print(blank)
+		p.stmt(s.Assign, false, ignoreMultiLine)
+		p.print(blank)
+		p.block(s.Body, 0)
+		*multiLine = true
+
+	case *ast.CommClause:
+		if s.Comm != nil {
+			p.print(token.CASE, blank)
+			p.stmt(s.Comm, false, ignoreMultiLine)
+		} else {
+			p.print(token.DEFAULT)
+		}
+		p.print(s.Colon, token.COLON)
+		p.stmtList(s.Body, 1, nextIsRBrace)
+
+	case *ast.SelectStmt:
+		p.print(token.SELECT, blank)
+		body := s.Body
+		if len(body.List) == 0 && !p.commentBefore(p.fset.Position(body.Rbrace)) {
+			// print empty select statement w/o comments on one line
+			p.print(body.Lbrace, token.LBRACE, body.Rbrace, token.RBRACE)
+		} else {
+			p.block(body, 0)
+			*multiLine = true
+		}
+
+	case *ast.ForStmt:
+		p.print(token.FOR)
+		p.controlClause(true, s.Init, s.Cond, s.Post)
+		p.block(s.Body, 1)
+		*multiLine = true
+
+	case *ast.RangeStmt:
+		p.print(token.FOR, blank)
+		p.expr(s.Key, multiLine)
+		if s.Value != nil {
+			p.print(token.COMMA, blank)
+			p.expr(s.Value, multiLine)
+		}
+		p.print(blank, s.TokPos, s.Tok, blank, token.RANGE, blank)
+		p.expr(stripParens(s.X), multiLine)
+		p.print(blank)
+		p.block(s.Body, 1)
+		*multiLine = true
+
+	default:
+		panic("unreachable")
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Declarations
+
+// The keepTypeColumn function determines if the type column of a series of
+// consecutive const or var declarations must be kept, or if initialization
+// values (V) can be placed in the type column (T) instead. The i'th entry
+// in the result slice is true if the type column in spec[i] must be kept.
+//
+// For example, the declaration:
+//
+//	const (
+//		foobar int = 42 // comment
+//		x          = 7  // comment
+//		foo
+//              bar = 991
+//	)
+//
+// leads to the type/values matrix below. A run of value columns (V) can
+// be moved into the type column if there is no type for any of the values
+// in that column (we only move entire columns so that they align properly).
+//
+//	matrix        formatted     result
+//                    matrix
+//	T  V    ->    T  V     ->   true      there is a T and so the type
+//	-  V          -  V          true      column must be kept
+//	-  -          -  -          false
+//	-  V          V  -          false     V is moved into T column
+//
+func keepTypeColumn(specs []ast.Spec) []bool {
+	m := make([]bool, len(specs))
+
+	populate := func(i, j int, keepType bool) {
+		if keepType {
+			for ; i < j; i++ {
+				m[i] = true
+			}
+		}
+	}
+
+	i0 := -1 // if i0 >= 0 we are in a run and i0 is the start of the run
+	var keepType bool
+	for i, s := range specs {
+		t := s.(*ast.ValueSpec)
+		if t.Values != nil {
+			if i0 < 0 {
+				// start of a run of ValueSpecs with non-nil Values
+				i0 = i
+				keepType = false
+			}
+		} else {
+			if i0 >= 0 {
+				// end of a run
+				populate(i0, i, keepType)
+				i0 = -1
+			}
+		}
+		if t.Type != nil {
+			keepType = true
+		}
+	}
+	if i0 >= 0 {
+		// end of a run
+		populate(i0, len(specs), keepType)
+	}
+
+	return m
+}
+
+func (p *printer) valueSpec(s *ast.ValueSpec, keepType, doIndent bool, multiLine *bool) {
+	p.setComment(s.Doc)
+	p.identList(s.Names, doIndent, multiLine) // always present
+	extraTabs := 3
+	if s.Type != nil || keepType {
+		p.print(vtab)
+		extraTabs--
+	}
+	if s.Type != nil {
+		p.expr(s.Type, multiLine)
+	}
+	if s.Values != nil {
+		p.print(vtab, token.ASSIGN)
+		p.exprList(token.NoPos, s.Values, 1, blankStart|commaSep, multiLine, token.NoPos)
+		extraTabs--
+	}
+	if s.Comment != nil {
+		for ; extraTabs > 0; extraTabs-- {
+			p.print(vtab)
+		}
+		p.setComment(s.Comment)
+	}
+}
+
+// The parameter n is the number of specs in the group. If doIndent is set,
+// multi-line identifier lists in the spec are indented when the first
+// linebreak is encountered.
+// Sets multiLine to true if the spec spans multiple lines.
+//
+func (p *printer) spec(spec ast.Spec, n int, doIndent bool, multiLine *bool) {
+	switch s := spec.(type) {
+	case *ast.ImportSpec:
+		p.setComment(s.Doc)
+		if s.Name != nil {
+			p.expr(s.Name, multiLine)
+			p.print(blank)
+		}
+		p.expr(s.Path, multiLine)
+		p.setComment(s.Comment)
+
+	case *ast.ValueSpec:
+		if n != 1 {
+			p.internalError("expected n = 1; got", n)
+		}
+		p.setComment(s.Doc)
+		p.identList(s.Names, doIndent, multiLine) // always present
+		if s.Type != nil {
+			p.print(blank)
+			p.expr(s.Type, multiLine)
+		}
+		if s.Values != nil {
+			p.print(blank, token.ASSIGN)
+			p.exprList(token.NoPos, s.Values, 1, blankStart|commaSep, multiLine, token.NoPos)
+		}
+		p.setComment(s.Comment)
+
+	case *ast.TypeSpec:
+		p.setComment(s.Doc)
+		p.expr(s.Name, multiLine)
+		if n == 1 {
+			p.print(blank)
+		} else {
+			p.print(vtab)
+		}
+		p.expr(s.Type, multiLine)
+		p.setComment(s.Comment)
+
+	default:
+		panic("unreachable")
+	}
+}
+
+// Sets multiLine to true if the declaration spans multiple lines.
+func (p *printer) genDecl(d *ast.GenDecl, multiLine *bool) {
+	p.setComment(d.Doc)
+	p.print(d.Pos(), d.Tok, blank)
+
+	if d.Lparen.IsValid() {
+		// group of parenthesized declarations
+		p.print(d.Lparen, token.LPAREN)
+		if n := len(d.Specs); n > 0 {
+			p.print(indent, formfeed)
+			if n > 1 && (d.Tok == token.CONST || d.Tok == token.VAR) {
+				// two or more grouped const/var declarations:
+				// determine if the type column must be kept
+				keepType := keepTypeColumn(d.Specs)
+				var ml bool
+				for i, s := range d.Specs {
+					if i > 0 {
+						p.linebreak(p.fset.Position(s.Pos()).Line, 1, ignore, ml)
+					}
+					ml = false
+					p.valueSpec(s.(*ast.ValueSpec), keepType[i], false, &ml)
+				}
+			} else {
+				var ml bool
+				for i, s := range d.Specs {
+					if i > 0 {
+						p.linebreak(p.fset.Position(s.Pos()).Line, 1, ignore, ml)
+					}
+					ml = false
+					p.spec(s, n, false, &ml)
+				}
+			}
+			p.print(unindent, formfeed)
+			*multiLine = true
+		}
+		p.print(d.Rparen, token.RPAREN)
+
+	} else {
+		// single declaration
+		p.spec(d.Specs[0], 1, true, multiLine)
+	}
+}
+
+// nodeSize determines the size of n in chars after formatting.
+// The result is <= maxSize if the node fits on one line with at
+// most maxSize chars and the formatted output doesn't contain
+// any control chars. Otherwise, the result is > maxSize.
+//
+func (p *printer) nodeSize(n ast.Node, maxSize int) (size int) {
+	// nodeSize invokes the printer, which may invoke nodeSize
+	// recursively. For deep composite literal nests, this can
+	// lead to an exponential algorithm. Remember previous
+	// results to prune the recursion (was issue 1628).
+	if size, found := p.nodeSizes[n]; found {
+		return size
+	}
+
+	size = maxSize + 1 // assume n doesn't fit
+	p.nodeSizes[n] = size
+
+	// nodeSize computation must be independent of particular
+	// style so that we always get the same decision; print
+	// in RawFormat
+	cfg := Config{Mode: RawFormat}
+	var buf bytes.Buffer
+	if _, err := cfg.fprint(&buf, p.fset, n, p.nodeSizes); err != nil {
+		return
+	}
+	if buf.Len() <= maxSize {
+		for _, ch := range buf.Bytes() {
+			if ch < ' ' {
+				return
+			}
+		}
+		size = buf.Len() // n fits
+		p.nodeSizes[n] = size
+	}
+	return
+}
+
+func (p *printer) isOneLineFunc(b *ast.BlockStmt, headerSize int) bool {
+	pos1 := b.Pos()
+	pos2 := b.Rbrace
+	if pos1.IsValid() && pos2.IsValid() && p.fset.Position(pos1).Line != p.fset.Position(pos2).Line {
+		// opening and closing brace are on different lines - don't make it a one-liner
+		return false
+	}
+	if len(b.List) > 5 || p.commentBefore(p.fset.Position(pos2)) {
+		// too many statements or there is a comment inside - don't make it a one-liner
+		return false
+	}
+	// otherwise, estimate body size
+	const maxSize = 100
+	bodySize := 0
+	for i, s := range b.List {
+		if i > 0 {
+			bodySize += 2 // space for a semicolon and blank
+		}
+		bodySize += p.nodeSize(s, maxSize)
+	}
+	return headerSize+bodySize <= maxSize
+}
+
+// Sets multiLine to true if the function body spans multiple lines.
+func (p *printer) funcBody(b *ast.BlockStmt, headerSize int, isLit bool, multiLine *bool) {
+	if b == nil {
+		return
+	}
+
+	if p.isOneLineFunc(b, headerSize) {
+		sep := vtab
+		if isLit {
+			sep = blank
+		}
+		p.print(sep, b.Lbrace, token.LBRACE)
+		if len(b.List) > 0 {
+			p.print(blank)
+			for i, s := range b.List {
+				if i > 0 {
+					p.print(token.SEMICOLON, blank)
+				}
+				p.stmt(s, i == len(b.List)-1, ignoreMultiLine)
+			}
+			p.print(blank)
+		}
+		p.print(b.Rbrace, token.RBRACE)
+		return
+	}
+
+	p.print(blank)
+	p.block(b, 1)
+	*multiLine = true
+}
+
+// distance returns the column difference between from and to if both
+// are on the same line; if they are on different lines (or unknown)
+// the result is infinity.
+func (p *printer) distance(from0 token.Pos, to token.Position) int {
+	from := p.fset.Position(from0)
+	if from.IsValid() && to.IsValid() && from.Line == to.Line {
+		return to.Column - from.Column
+	}
+	return infinity
+}
+
+// Sets multiLine to true if the declaration spans multiple lines.
+func (p *printer) funcDecl(d *ast.FuncDecl, multiLine *bool) {
+	p.setComment(d.Doc)
+	p.print(d.Pos(), token.FUNC, blank)
+	if d.Recv != nil {
+		p.parameters(d.Recv, multiLine) // method: print receiver
+		p.print(blank)
+	}
+	p.expr(d.Name, multiLine)
+	p.signature(d.Type.Params, d.Type.Results, multiLine)
+	p.funcBody(d.Body, p.distance(d.Pos(), p.pos), false, multiLine)
+}
+
+// Sets multiLine to true if the declaration spans multiple lines.
+func (p *printer) decl(decl ast.Decl, multiLine *bool) {
+	switch d := decl.(type) {
+	case *ast.BadDecl:
+		p.print(d.Pos(), "BadDecl")
+	case *ast.GenDecl:
+		p.genDecl(d, multiLine)
+	case *ast.FuncDecl:
+		p.funcDecl(d, multiLine)
+	default:
+		panic("unreachable")
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Files
+
+func declToken(decl ast.Decl) (tok token.Token) {
+	tok = token.ILLEGAL
+	switch d := decl.(type) {
+	case *ast.GenDecl:
+		tok = d.Tok
+	case *ast.FuncDecl:
+		tok = token.FUNC
+	}
+	return
+}
+
+func (p *printer) file(src *ast.File) {
+	p.setComment(src.Doc)
+	p.print(src.Pos(), token.PACKAGE, blank)
+	p.expr(src.Name, ignoreMultiLine)
+
+	if len(src.Decls) > 0 {
+		tok := token.ILLEGAL
+		for _, d := range src.Decls {
+			prev := tok
+			tok = declToken(d)
+			// if the declaration token changed (e.g., from CONST to TYPE)
+			// print an empty line between top-level declarations
+			min := 1
+			if prev != tok {
+				min = 2
+			}
+			p.linebreak(p.fset.Position(d.Pos()).Line, min, ignore, false)
+			p.decl(d, ignoreMultiLine)
+		}
+	}
+
+	p.print(newline)
+}
diff --git a/src/pkg/go/printer/performance_test.go b/src/pkg/go/printer/performance_test.go
new file mode 100644
index 000000000..84fb2808e
--- /dev/null
+++ b/src/pkg/go/printer/performance_test.go
@@ -0,0 +1,58 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements a simple printer performance benchmark:
+// gotest -bench=BenchmarkPrint 
+
+package printer
+
+import (
+	"bytes"
+	"go/ast"
+	"go/parser"
+	"io"
+	"io/ioutil"
+	"log"
+	"testing"
+)
+
+var testfile *ast.File
+
+func testprint(out io.Writer, file *ast.File) {
+	if _, err := (&Config{TabIndent | UseSpaces, 8}).Fprint(out, fset, file); err != nil {
+		log.Fatalf("print error: %s", err)
+	}
+}
+
+// cannot initialize in init because (printer) Fprint launches goroutines.
+func initialize() {
+	const filename = "testdata/parser.go"
+
+	src, err := ioutil.ReadFile(filename)
+	if err != nil {
+		log.Fatalf("%s", err)
+	}
+
+	file, err := parser.ParseFile(fset, filename, src, parser.ParseComments)
+	if err != nil {
+		log.Fatalf("%s", err)
+	}
+
+	var buf bytes.Buffer
+	testprint(&buf, file)
+	if !bytes.Equal(buf.Bytes(), src) {
+		log.Fatalf("print error: %s not idempotent", filename)
+	}
+
+	testfile = file
+}
+
+func BenchmarkPrint(b *testing.B) {
+	if testfile == nil {
+		initialize()
+	}
+	for i := 0; i < b.N; i++ {
+		testprint(ioutil.Discard, testfile)
+	}
+}
diff --git a/src/pkg/go/printer/printer.go b/src/pkg/go/printer/printer.go
new file mode 100644
index 000000000..871fefa0c
--- /dev/null
+++ b/src/pkg/go/printer/printer.go
@@ -0,0 +1,1012 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package printer implements printing of AST nodes.
+package printer
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/token"
+	"io"
+	"os"
+	"path/filepath"
+	"runtime"
+	"tabwriter"
+)
+
+const debug = false // enable for debugging
+
+
+type whiteSpace int
+
+const (
+	ignore   = whiteSpace(0)
+	blank    = whiteSpace(' ')
+	vtab     = whiteSpace('\v')
+	newline  = whiteSpace('\n')
+	formfeed = whiteSpace('\f')
+	indent   = whiteSpace('>')
+	unindent = whiteSpace('<')
+)
+
+var (
+	esc       = []byte{tabwriter.Escape}
+	htab      = []byte{'\t'}
+	htabs     = []byte("\t\t\t\t\t\t\t\t")
+	newlines  = []byte("\n\n\n\n\n\n\n\n") // more than the max determined by nlines
+	formfeeds = []byte("\f\f\f\f\f\f\f\f") // more than the max determined by nlines
+)
+
+// Special positions
+var noPos token.Position // use noPos when a position is needed but not known
+var infinity = 1 << 30
+
+// Use ignoreMultiLine if the multiLine information is not important.
+var ignoreMultiLine = new(bool)
+
+// A pmode value represents the current printer mode.
+type pmode int
+
+const (
+	inLiteral pmode = 1 << iota
+	noExtraLinebreak
+)
+
+type printer struct {
+	// Configuration (does not change after initialization)
+	output io.Writer
+	Config
+	fset   *token.FileSet
+	errors chan os.Error
+
+	// Current state
+	written int         // number of bytes written
+	indent  int         // current indentation
+	mode    pmode       // current printer mode
+	lastTok token.Token // the last token printed (token.ILLEGAL if it's whitespace)
+
+	// Reused buffers
+	wsbuf  []whiteSpace // delayed white space
+	litbuf bytes.Buffer // for creation of escaped literals and comments
+
+	// The (possibly estimated) position in the generated output;
+	// in AST space (i.e., pos is set whenever a token position is
+	// known accurately, and updated dependending on what has been
+	// written).
+	pos token.Position
+
+	// The value of pos immediately after the last item has been
+	// written using writeItem.
+	last token.Position
+
+	// The list of all source comments, in order of appearance.
+	comments        []*ast.CommentGroup // may be nil
+	cindex          int                 // current comment index
+	useNodeComments bool                // if not set, ignore lead and line comments of nodes
+
+	// Cache of already computed node sizes.
+	nodeSizes map[ast.Node]int
+}
+
+func (p *printer) init(output io.Writer, cfg *Config, fset *token.FileSet, nodeSizes map[ast.Node]int) {
+	p.output = output
+	p.Config = *cfg
+	p.fset = fset
+	p.errors = make(chan os.Error)
+	p.wsbuf = make([]whiteSpace, 0, 16) // whitespace sequences are short
+	p.nodeSizes = nodeSizes
+}
+
+func (p *printer) internalError(msg ...interface{}) {
+	if debug {
+		fmt.Print(p.pos.String() + ": ")
+		fmt.Println(msg...)
+		panic("go/printer")
+	}
+}
+
+// escape escapes string s by bracketing it with tabwriter.Escape.
+// Escaped strings pass through tabwriter unchanged. (Note that
+// valid Go programs cannot contain tabwriter.Escape bytes since
+// they do not appear in legal UTF-8 sequences).
+//
+func (p *printer) escape(s string) string {
+	p.litbuf.Reset()
+	p.litbuf.WriteByte(tabwriter.Escape)
+	p.litbuf.WriteString(s)
+	p.litbuf.WriteByte(tabwriter.Escape)
+	return p.litbuf.String()
+}
+
+// nlines returns the adjusted number of linebreaks given the desired number
+// of breaks n such that min <= result <= max.
+//
+func (p *printer) nlines(n, min int) int {
+	const max = 2 // max. number of newlines
+	switch {
+	case n < min:
+		return min
+	case n > max:
+		return max
+	}
+	return n
+}
+
+// write0 writes raw (uninterpreted) data to p.output and handles errors.
+// write0 does not indent after newlines, and does not HTML-escape or update p.pos.
+//
+func (p *printer) write0(data []byte) {
+	if len(data) > 0 {
+		n, err := p.output.Write(data)
+		p.written += n
+		if err != nil {
+			p.errors <- err
+			runtime.Goexit()
+		}
+	}
+}
+
+// write interprets data and writes it to p.output. It inserts indentation
+// after a line break unless in a tabwriter escape sequence.
+// It updates p.pos as a side-effect.
+//
+func (p *printer) write(data []byte) {
+	i0 := 0
+	for i, b := range data {
+		switch b {
+		case '\n', '\f':
+			// write segment ending in b
+			p.write0(data[i0 : i+1])
+
+			// update p.pos
+			p.pos.Offset += i + 1 - i0
+			p.pos.Line++
+			p.pos.Column = 1
+
+			if p.mode&inLiteral == 0 {
+				// write indentation
+				// use "hard" htabs - indentation columns
+				// must not be discarded by the tabwriter
+				j := p.indent
+				for ; j > len(htabs); j -= len(htabs) {
+					p.write0(htabs)
+				}
+				p.write0(htabs[0:j])
+
+				// update p.pos
+				p.pos.Offset += p.indent
+				p.pos.Column += p.indent
+			}
+
+			// next segment start
+			i0 = i + 1
+
+		case tabwriter.Escape:
+			p.mode ^= inLiteral
+
+			// ignore escape chars introduced by printer - they are
+			// invisible and must not affect p.pos (was issue #1089)
+			p.pos.Offset--
+			p.pos.Column--
+		}
+	}
+
+	// write remaining segment
+	p.write0(data[i0:])
+
+	// update p.pos
+	d := len(data) - i0
+	p.pos.Offset += d
+	p.pos.Column += d
+}
+
+func (p *printer) writeNewlines(n int, useFF bool) {
+	if n > 0 {
+		n = p.nlines(n, 0)
+		if useFF {
+			p.write(formfeeds[0:n])
+		} else {
+			p.write(newlines[0:n])
+		}
+	}
+}
+
+// writeItem writes data at position pos. data is the text corresponding to
+// a single lexical token, but may also be comment text. pos is the actual
+// (or at least very accurately estimated) position of the data in the original
+// source text. writeItem updates p.last to the position immediately following
+// the data.
+//
+func (p *printer) writeItem(pos token.Position, data string) {
+	if pos.IsValid() {
+		// continue with previous position if we don't have a valid pos
+		if p.last.IsValid() && p.last.Filename != pos.Filename {
+			// the file has changed - reset state
+			// (used when printing merged ASTs of different files
+			// e.g., the result of ast.MergePackageFiles)
+			p.indent = 0
+			p.mode = 0
+			p.wsbuf = p.wsbuf[0:0]
+		}
+		p.pos = pos
+	}
+	if debug {
+		// do not update p.pos - use write0
+		_, filename := filepath.Split(pos.Filename)
+		p.write0([]byte(fmt.Sprintf("[%s:%d:%d]", filename, pos.Line, pos.Column)))
+	}
+	p.write([]byte(data))
+	p.last = p.pos
+}
+
+// writeCommentPrefix writes the whitespace before a comment.
+// If there is any pending whitespace, it consumes as much of
+// it as is likely to help position the comment nicely.
+// pos is the comment position, next the position of the item
+// after all pending comments, prev is the previous comment in
+// a group of comments (or nil), and isKeyword indicates if the
+// next item is a keyword.
+//
+func (p *printer) writeCommentPrefix(pos, next token.Position, prev *ast.Comment, isKeyword bool) {
+	if p.written == 0 {
+		// the comment is the first item to be printed - don't write any whitespace
+		return
+	}
+
+	if pos.IsValid() && pos.Filename != p.last.Filename {
+		// comment in a different file - separate with newlines (writeNewlines will limit the number)
+		p.writeNewlines(10, true)
+		return
+	}
+
+	if pos.Line == p.last.Line && (prev == nil || prev.Text[1] != '/') {
+		// comment on the same line as last item:
+		// separate with at least one separator
+		hasSep := false
+		if prev == nil {
+			// first comment of a comment group
+			j := 0
+			for i, ch := range p.wsbuf {
+				switch ch {
+				case blank:
+					// ignore any blanks before a comment
+					p.wsbuf[i] = ignore
+					continue
+				case vtab:
+					// respect existing tabs - important
+					// for proper formatting of commented structs
+					hasSep = true
+					continue
+				case indent:
+					// apply pending indentation
+					continue
+				}
+				j = i
+				break
+			}
+			p.writeWhitespace(j)
+		}
+		// make sure there is at least one separator
+		if !hasSep {
+			if pos.Line == next.Line {
+				// next item is on the same line as the comment
+				// (which must be a /*-style comment): separate
+				// with a blank instead of a tab
+				p.write([]byte{' '})
+			} else {
+				p.write(htab)
+			}
+		}
+
+	} else {
+		// comment on a different line:
+		// separate with at least one line break
+		if prev == nil {
+			// first comment of a comment group
+			j := 0
+			for i, ch := range p.wsbuf {
+				switch ch {
+				case blank, vtab:
+					// ignore any horizontal whitespace before line breaks
+					p.wsbuf[i] = ignore
+					continue
+				case indent:
+					// apply pending indentation
+					continue
+				case unindent:
+					// if the next token is a keyword, apply the outdent
+					// if it appears that the comment is aligned with the
+					// keyword; otherwise assume the outdent is part of a
+					// closing block and stop (this scenario appears with
+					// comments before a case label where the comments
+					// apply to the next case instead of the current one)
+					if isKeyword && pos.Column == next.Column {
+						continue
+					}
+				case newline, formfeed:
+					// TODO(gri): may want to keep formfeed info in some cases
+					p.wsbuf[i] = ignore
+				}
+				j = i
+				break
+			}
+			p.writeWhitespace(j)
+		}
+		// use formfeeds to break columns before a comment;
+		// this is analogous to using formfeeds to separate
+		// individual lines of /*-style comments - but make
+		// sure there is at least one line break if the previous
+		// comment was a line comment
+		n := pos.Line - p.last.Line // if !pos.IsValid(), pos.Line == 0, and n will be 0
+		if n <= 0 && prev != nil && prev.Text[1] == '/' {
+			n = 1
+		}
+		p.writeNewlines(n, true)
+	}
+}
+
+// TODO(gri): It should be possible to convert the code below from using
+//            []byte to string and in the process eliminate some conversions.
+
+// Split comment text into lines
+func split(text []byte) [][]byte {
+	// count lines (comment text never ends in a newline)
+	n := 1
+	for _, c := range text {
+		if c == '\n' {
+			n++
+		}
+	}
+
+	// split
+	lines := make([][]byte, n)
+	n = 0
+	i := 0
+	for j, c := range text {
+		if c == '\n' {
+			lines[n] = text[i:j] // exclude newline
+			i = j + 1            // discard newline
+			n++
+		}
+	}
+	lines[n] = text[i:]
+
+	return lines
+}
+
+func isBlank(s []byte) bool {
+	for _, b := range s {
+		if b > ' ' {
+			return false
+		}
+	}
+	return true
+}
+
+func commonPrefix(a, b []byte) []byte {
+	i := 0
+	for i < len(a) && i < len(b) && a[i] == b[i] && (a[i] <= ' ' || a[i] == '*') {
+		i++
+	}
+	return a[0:i]
+}
+
+func stripCommonPrefix(lines [][]byte) {
+	if len(lines) < 2 {
+		return // at most one line - nothing to do
+	}
+	// len(lines) >= 2
+
+	// The heuristic in this function tries to handle a few
+	// common patterns of /*-style comments: Comments where
+	// the opening /* and closing */ are aligned and the
+	// rest of the comment text is aligned and indented with
+	// blanks or tabs, cases with a vertical "line of stars"
+	// on the left, and cases where the closing */ is on the
+	// same line as the last comment text.
+
+	// Compute maximum common white prefix of all but the first,
+	// last, and blank lines, and replace blank lines with empty
+	// lines (the first line starts with /* and has no prefix).
+	// In case of two-line comments, consider the last line for
+	// the prefix computation since otherwise the prefix would
+	// be empty.
+	//
+	// Note that the first and last line are never empty (they
+	// contain the opening /* and closing */ respectively) and
+	// thus they can be ignored by the blank line check.
+	var prefix []byte
+	if len(lines) > 2 {
+		for i, line := range lines[1 : len(lines)-1] {
+			switch {
+			case isBlank(line):
+				lines[1+i] = nil // range starts at line 1
+			case prefix == nil:
+				prefix = commonPrefix(line, line)
+			default:
+				prefix = commonPrefix(prefix, line)
+			}
+		}
+	} else { // len(lines) == 2
+		line := lines[1]
+		prefix = commonPrefix(line, line)
+	}
+
+	/*
+	 * Check for vertical "line of stars" and correct prefix accordingly.
+	 */
+	lineOfStars := false
+	if i := bytes.Index(prefix, []byte{'*'}); i >= 0 {
+		// Line of stars present.
+		if i > 0 && prefix[i-1] == ' ' {
+			i-- // remove trailing blank from prefix so stars remain aligned
+		}
+		prefix = prefix[0:i]
+		lineOfStars = true
+	} else {
+		// No line of stars present.
+		// Determine the white space on the first line after the /*
+		// and before the beginning of the comment text, assume two
+		// blanks instead of the /* unless the first character after
+		// the /* is a tab. If the first comment line is empty but
+		// for the opening /*, assume up to 3 blanks or a tab. This
+		// whitespace may be found as suffix in the common prefix.
+		first := lines[0]
+		if isBlank(first[2:]) {
+			// no comment text on the first line:
+			// reduce prefix by up to 3 blanks or a tab
+			// if present - this keeps comment text indented
+			// relative to the /* and */'s if it was indented
+			// in the first place
+			i := len(prefix)
+			for n := 0; n < 3 && i > 0 && prefix[i-1] == ' '; n++ {
+				i--
+			}
+			if i == len(prefix) && i > 0 && prefix[i-1] == '\t' {
+				i--
+			}
+			prefix = prefix[0:i]
+		} else {
+			// comment text on the first line
+			suffix := make([]byte, len(first))
+			n := 2 // start after opening /*
+			for n < len(first) && first[n] <= ' ' {
+				suffix[n] = first[n]
+				n++
+			}
+			if n > 2 && suffix[2] == '\t' {
+				// assume the '\t' compensates for the /*
+				suffix = suffix[2:n]
+			} else {
+				// otherwise assume two blanks
+				suffix[0], suffix[1] = ' ', ' '
+				suffix = suffix[0:n]
+			}
+			// Shorten the computed common prefix by the length of
+			// suffix, if it is found as suffix of the prefix.
+			if bytes.HasSuffix(prefix, suffix) {
+				prefix = prefix[0 : len(prefix)-len(suffix)]
+			}
+		}
+	}
+
+	// Handle last line: If it only contains a closing */, align it
+	// with the opening /*, otherwise align the text with the other
+	// lines.
+	last := lines[len(lines)-1]
+	closing := []byte("*/")
+	i := bytes.Index(last, closing)
+	if isBlank(last[0:i]) {
+		// last line only contains closing */
+		var sep []byte
+		if lineOfStars {
+			// insert an aligning blank
+			sep = []byte{' '}
+		}
+		lines[len(lines)-1] = bytes.Join([][]byte{prefix, closing}, sep)
+	} else {
+		// last line contains more comment text - assume
+		// it is aligned like the other lines
+		prefix = commonPrefix(prefix, last)
+	}
+
+	// Remove the common prefix from all but the first and empty lines.
+	for i, line := range lines[1:] {
+		if len(line) != 0 {
+			lines[1+i] = line[len(prefix):] // range starts at line 1
+		}
+	}
+}
+
+func (p *printer) writeComment(comment *ast.Comment) {
+	text := comment.Text
+
+	// shortcut common case of //-style comments
+	if text[1] == '/' {
+		p.writeItem(p.fset.Position(comment.Pos()), p.escape(text))
+		return
+	}
+
+	// for /*-style comments, print line by line and let the
+	// write function take care of the proper indentation
+	lines := split([]byte(text))
+	stripCommonPrefix(lines)
+
+	// write comment lines, separated by formfeed,
+	// without a line break after the last line
+	linebreak := formfeeds[0:1]
+	pos := p.fset.Position(comment.Pos())
+	for i, line := range lines {
+		if i > 0 {
+			p.write(linebreak)
+			pos = p.pos
+		}
+		if len(line) > 0 {
+			p.writeItem(pos, p.escape(string(line)))
+		}
+	}
+}
+
+// writeCommentSuffix writes a line break after a comment if indicated
+// and processes any leftover indentation information. If a line break
+// is needed, the kind of break (newline vs formfeed) depends on the
+// pending whitespace. writeCommentSuffix returns true if a pending
+// formfeed was dropped from the whitespace buffer.
+//
+func (p *printer) writeCommentSuffix(needsLinebreak bool) (droppedFF bool) {
+	for i, ch := range p.wsbuf {
+		switch ch {
+		case blank, vtab:
+			// ignore trailing whitespace
+			p.wsbuf[i] = ignore
+		case indent, unindent:
+			// don't lose indentation information
+		case newline, formfeed:
+			// if we need a line break, keep exactly one
+			// but remember if we dropped any formfeeds
+			if needsLinebreak {
+				needsLinebreak = false
+			} else {
+				if ch == formfeed {
+					droppedFF = true
+				}
+				p.wsbuf[i] = ignore
+			}
+		}
+	}
+	p.writeWhitespace(len(p.wsbuf))
+
+	// make sure we have a line break
+	if needsLinebreak {
+		p.write([]byte{'\n'})
+	}
+
+	return
+}
+
+// intersperseComments consumes all comments that appear before the next token
+// tok and prints it together with the buffered whitespace (i.e., the whitespace
+// that needs to be written before the next token). A heuristic is used to mix
+// the comments and whitespace. intersperseComments returns true if a pending
+// formfeed was dropped from the whitespace buffer.
+//
+func (p *printer) intersperseComments(next token.Position, tok token.Token) (droppedFF bool) {
+	var last *ast.Comment
+	for ; p.commentBefore(next); p.cindex++ {
+		for _, c := range p.comments[p.cindex].List {
+			p.writeCommentPrefix(p.fset.Position(c.Pos()), next, last, tok.IsKeyword())
+			p.writeComment(c)
+			last = c
+		}
+	}
+
+	if last != nil {
+		if last.Text[1] == '*' && p.fset.Position(last.Pos()).Line == next.Line {
+			// the last comment is a /*-style comment and the next item
+			// follows on the same line: separate with an extra blank
+			p.write([]byte{' '})
+		}
+		// ensure that there is a line break after a //-style comment,
+		// before a closing '}' unless explicitly disabled, or at eof
+		needsLinebreak :=
+			last.Text[1] == '/' ||
+				tok == token.RBRACE && p.mode&noExtraLinebreak == 0 ||
+				tok == token.EOF
+		return p.writeCommentSuffix(needsLinebreak)
+	}
+
+	// no comment was written - we should never reach here since
+	// intersperseComments should not be called in that case
+	p.internalError("intersperseComments called without pending comments")
+	return false
+}
+
+// whiteWhitespace writes the first n whitespace entries.
+func (p *printer) writeWhitespace(n int) {
+	// write entries
+	var data [1]byte
+	for i := 0; i < n; i++ {
+		switch ch := p.wsbuf[i]; ch {
+		case ignore:
+			// ignore!
+		case indent:
+			p.indent++
+		case unindent:
+			p.indent--
+			if p.indent < 0 {
+				p.internalError("negative indentation:", p.indent)
+				p.indent = 0
+			}
+		case newline, formfeed:
+			// A line break immediately followed by a "correcting"
+			// unindent is swapped with the unindent - this permits
+			// proper label positioning. If a comment is between
+			// the line break and the label, the unindent is not
+			// part of the comment whitespace prefix and the comment
+			// will be positioned correctly indented.
+			if i+1 < n && p.wsbuf[i+1] == unindent {
+				// Use a formfeed to terminate the current section.
+				// Otherwise, a long label name on the next line leading
+				// to a wide column may increase the indentation column
+				// of lines before the label; effectively leading to wrong
+				// indentation.
+				p.wsbuf[i], p.wsbuf[i+1] = unindent, formfeed
+				i-- // do it again
+				continue
+			}
+			fallthrough
+		default:
+			data[0] = byte(ch)
+			p.write(data[0:])
+		}
+	}
+
+	// shift remaining entries down
+	i := 0
+	for ; n < len(p.wsbuf); n++ {
+		p.wsbuf[i] = p.wsbuf[n]
+		i++
+	}
+	p.wsbuf = p.wsbuf[0:i]
+}
+
+// ----------------------------------------------------------------------------
+// Printing interface
+
+
+func mayCombine(prev token.Token, next byte) (b bool) {
+	switch prev {
+	case token.INT:
+		b = next == '.' // 1.
+	case token.ADD:
+		b = next == '+' // ++
+	case token.SUB:
+		b = next == '-' // --
+	case token.QUO:
+		b = next == '*' // /*
+	case token.LSS:
+		b = next == '-' || next == '<' // <- or <<
+	case token.AND:
+		b = next == '&' || next == '^' // && or &^
+	}
+	return
+}
+
+// print prints a list of "items" (roughly corresponding to syntactic
+// tokens, but also including whitespace and formatting information).
+// It is the only print function that should be called directly from
+// any of the AST printing functions in nodes.go.
+//
+// Whitespace is accumulated until a non-whitespace token appears. Any
+// comments that need to appear before that token are printed first,
+// taking into account the amount and structure of any pending white-
+// space for best comment placement. Then, any leftover whitespace is
+// printed, followed by the actual token.
+//
+func (p *printer) print(args ...interface{}) {
+	for _, f := range args {
+		next := p.pos // estimated position of next item
+		var data string
+		var tok token.Token
+
+		switch x := f.(type) {
+		case pmode:
+			// toggle printer mode
+			p.mode ^= x
+		case whiteSpace:
+			if x == ignore {
+				// don't add ignore's to the buffer; they
+				// may screw up "correcting" unindents (see
+				// LabeledStmt)
+				break
+			}
+			i := len(p.wsbuf)
+			if i == cap(p.wsbuf) {
+				// Whitespace sequences are very short so this should
+				// never happen. Handle gracefully (but possibly with
+				// bad comment placement) if it does happen.
+				p.writeWhitespace(i)
+				i = 0
+			}
+			p.wsbuf = p.wsbuf[0 : i+1]
+			p.wsbuf[i] = x
+		case *ast.Ident:
+			data = x.Name
+			tok = token.IDENT
+		case *ast.BasicLit:
+			data = p.escape(x.Value)
+			tok = x.Kind
+		case token.Token:
+			s := x.String()
+			if mayCombine(p.lastTok, s[0]) {
+				// the previous and the current token must be
+				// separated by a blank otherwise they combine
+				// into a different incorrect token sequence
+				// (except for token.INT followed by a '.' this
+				// should never happen because it is taken care
+				// of via binary expression formatting)
+				if len(p.wsbuf) != 0 {
+					p.internalError("whitespace buffer not empty")
+				}
+				p.wsbuf = p.wsbuf[0:1]
+				p.wsbuf[0] = ' '
+			}
+			data = s
+			tok = x
+		case token.Pos:
+			if x.IsValid() {
+				next = p.fset.Position(x) // accurate position of next item
+			}
+			tok = p.lastTok
+		default:
+			fmt.Fprintf(os.Stderr, "print: unsupported argument type %T\n", f)
+			panic("go/printer type")
+		}
+		p.lastTok = tok
+		p.pos = next
+
+		if data != "" {
+			droppedFF := p.flush(next, tok)
+
+			// intersperse extra newlines if present in the source
+			// (don't do this in flush as it will cause extra newlines
+			// at the end of a file) - use formfeeds if we dropped one
+			// before
+			p.writeNewlines(next.Line-p.pos.Line, droppedFF)
+
+			p.writeItem(next, data)
+		}
+	}
+}
+
+// commentBefore returns true iff the current comment occurs
+// before the next position in the source code.
+//
+func (p *printer) commentBefore(next token.Position) bool {
+	return p.cindex < len(p.comments) && p.fset.Position(p.comments[p.cindex].List[0].Pos()).Offset < next.Offset
+}
+
+// Flush prints any pending comments and whitespace occurring
+// textually before the position of the next token tok. Flush
+// returns true if a pending formfeed character was dropped
+// from the whitespace buffer as a result of interspersing
+// comments.
+//
+func (p *printer) flush(next token.Position, tok token.Token) (droppedFF bool) {
+	if p.commentBefore(next) {
+		// if there are comments before the next item, intersperse them
+		droppedFF = p.intersperseComments(next, tok)
+	} else {
+		// otherwise, write any leftover whitespace
+		p.writeWhitespace(len(p.wsbuf))
+	}
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Trimmer
+
+// A trimmer is an io.Writer filter for stripping tabwriter.Escape
+// characters, trailing blanks and tabs, and for converting formfeed
+// and vtab characters into newlines and htabs (in case no tabwriter
+// is used). Text bracketed by tabwriter.Escape characters is passed
+// through unchanged.
+//
+type trimmer struct {
+	output io.Writer
+	state  int
+	space  bytes.Buffer
+}
+
+// trimmer is implemented as a state machine.
+// It can be in one of the following states:
+const (
+	inSpace  = iota // inside space
+	inEscape        // inside text bracketed by tabwriter.Escapes
+	inText          // inside text
+)
+
+// Design note: It is tempting to eliminate extra blanks occurring in
+//              whitespace in this function as it could simplify some
+//              of the blanks logic in the node printing functions.
+//              However, this would mess up any formatting done by
+//              the tabwriter.
+
+func (p *trimmer) Write(data []byte) (n int, err os.Error) {
+	// invariants:
+	// p.state == inSpace:
+	//	p.space is unwritten
+	// p.state == inEscape, inText:
+	//	data[m:n] is unwritten
+	m := 0
+	var b byte
+	for n, b = range data {
+		if b == '\v' {
+			b = '\t' // convert to htab
+		}
+		switch p.state {
+		case inSpace:
+			switch b {
+			case '\t', ' ':
+				p.space.WriteByte(b) // WriteByte returns no errors
+			case '\n', '\f':
+				p.space.Reset()                        // discard trailing space
+				_, err = p.output.Write(newlines[0:1]) // write newline
+			case tabwriter.Escape:
+				_, err = p.output.Write(p.space.Bytes())
+				p.state = inEscape
+				m = n + 1 // +1: skip tabwriter.Escape
+			default:
+				_, err = p.output.Write(p.space.Bytes())
+				p.state = inText
+				m = n
+			}
+		case inEscape:
+			if b == tabwriter.Escape {
+				_, err = p.output.Write(data[m:n])
+				p.state = inSpace
+				p.space.Reset()
+			}
+		case inText:
+			switch b {
+			case '\t', ' ':
+				_, err = p.output.Write(data[m:n])
+				p.state = inSpace
+				p.space.Reset()
+				p.space.WriteByte(b) // WriteByte returns no errors
+			case '\n', '\f':
+				_, err = p.output.Write(data[m:n])
+				p.state = inSpace
+				p.space.Reset()
+				_, err = p.output.Write(newlines[0:1]) // write newline
+			case tabwriter.Escape:
+				_, err = p.output.Write(data[m:n])
+				p.state = inEscape
+				m = n + 1 // +1: skip tabwriter.Escape
+			}
+		default:
+			panic("unreachable")
+		}
+		if err != nil {
+			return
+		}
+	}
+	n = len(data)
+
+	switch p.state {
+	case inEscape, inText:
+		_, err = p.output.Write(data[m:n])
+		p.state = inSpace
+		p.space.Reset()
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Public interface
+
+// General printing is controlled with these Config.Mode flags.
+const (
+	RawFormat uint = 1 << iota // do not use a tabwriter; if set, UseSpaces is ignored
+	TabIndent                  // use tabs for indentation independent of UseSpaces
+	UseSpaces                  // use spaces instead of tabs for alignment
+)
+
+// A Config node controls the output of Fprint.
+type Config struct {
+	Mode     uint // default: 0
+	Tabwidth int  // default: 8
+}
+
+// fprint implements Fprint and takes a nodesSizes map for setting up the printer state.
+func (cfg *Config) fprint(output io.Writer, fset *token.FileSet, node interface{}, nodeSizes map[ast.Node]int) (int, os.Error) {
+	// redirect output through a trimmer to eliminate trailing whitespace
+	// (Input to a tabwriter must be untrimmed since trailing tabs provide
+	// formatting information. The tabwriter could provide trimming
+	// functionality but no tabwriter is used when RawFormat is set.)
+	output = &trimmer{output: output}
+
+	// setup tabwriter if needed and redirect output
+	var tw *tabwriter.Writer
+	if cfg.Mode&RawFormat == 0 {
+		minwidth := cfg.Tabwidth
+
+		padchar := byte('\t')
+		if cfg.Mode&UseSpaces != 0 {
+			padchar = ' '
+		}
+
+		twmode := tabwriter.DiscardEmptyColumns
+		if cfg.Mode&TabIndent != 0 {
+			minwidth = 0
+			twmode |= tabwriter.TabIndent
+		}
+
+		tw = tabwriter.NewWriter(output, minwidth, cfg.Tabwidth, 1, padchar, twmode)
+		output = tw
+	}
+
+	// setup printer and print node
+	var p printer
+	p.init(output, cfg, fset, nodeSizes)
+	go func() {
+		switch n := node.(type) {
+		case ast.Expr:
+			p.useNodeComments = true
+			p.expr(n, ignoreMultiLine)
+		case ast.Stmt:
+			p.useNodeComments = true
+			// A labeled statement will un-indent to position the
+			// label. Set indent to 1 so we don't get indent "underflow".
+			if _, labeledStmt := n.(*ast.LabeledStmt); labeledStmt {
+				p.indent = 1
+			}
+			p.stmt(n, false, ignoreMultiLine)
+		case ast.Decl:
+			p.useNodeComments = true
+			p.decl(n, ignoreMultiLine)
+		case ast.Spec:
+			p.useNodeComments = true
+			p.spec(n, 1, false, ignoreMultiLine)
+		case *ast.File:
+			p.comments = n.Comments
+			p.useNodeComments = n.Comments == nil
+			p.file(n)
+		default:
+			p.errors <- fmt.Errorf("printer.Fprint: unsupported node type %T", n)
+			runtime.Goexit()
+		}
+		p.flush(token.Position{Offset: infinity, Line: infinity}, token.EOF)
+		p.errors <- nil // no errors
+	}()
+	err := <-p.errors // wait for completion of goroutine
+
+	// flush tabwriter, if any
+	if tw != nil {
+		tw.Flush() // ignore errors
+	}
+
+	return p.written, err
+}
+
+// Fprint "pretty-prints" an AST node to output and returns the number
+// of bytes written and an error (if any) for a given configuration cfg.
+// Position information is interpreted relative to the file set fset.
+// The node type must be *ast.File, or assignment-compatible to ast.Expr,
+// ast.Decl, ast.Spec, or ast.Stmt.
+//
+func (cfg *Config) Fprint(output io.Writer, fset *token.FileSet, node interface{}) (int, os.Error) {
+	return cfg.fprint(output, fset, node, make(map[ast.Node]int))
+}
+
+// Fprint "pretty-prints" an AST node to output.
+// It calls Config.Fprint with default settings.
+//
+func Fprint(output io.Writer, fset *token.FileSet, node interface{}) os.Error {
+	_, err := (&Config{Tabwidth: 8}).Fprint(output, fset, node) // don't care about number of bytes written
+	return err
+}
diff --git a/src/pkg/go/printer/printer_test.go b/src/pkg/go/printer/printer_test.go
new file mode 100644
index 000000000..ff2d906b5
--- /dev/null
+++ b/src/pkg/go/printer/printer_test.go
@@ -0,0 +1,194 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package printer
+
+import (
+	"bytes"
+	"flag"
+	"io/ioutil"
+	"go/ast"
+	"go/parser"
+	"go/token"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+const (
+	dataDir  = "testdata"
+	tabwidth = 8
+)
+
+var update = flag.Bool("update", false, "update golden files")
+
+var fset = token.NewFileSet()
+
+func lineString(text []byte, i int) string {
+	i0 := i
+	for i < len(text) && text[i] != '\n' {
+		i++
+	}
+	return string(text[i0:i])
+}
+
+type checkMode uint
+
+const (
+	export checkMode = 1 << iota
+	rawFormat
+)
+
+func runcheck(t *testing.T, source, golden string, mode checkMode) {
+	// parse source
+	prog, err := parser.ParseFile(fset, source, nil, parser.ParseComments)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	// filter exports if necessary
+	if mode&export != 0 {
+		ast.FileExports(prog) // ignore result
+		prog.Comments = nil   // don't print comments that are not in AST
+	}
+
+	// determine printer configuration
+	cfg := Config{Tabwidth: tabwidth}
+	if mode&rawFormat != 0 {
+		cfg.Mode |= RawFormat
+	}
+
+	// format source
+	var buf bytes.Buffer
+	if _, err := cfg.Fprint(&buf, fset, prog); err != nil {
+		t.Error(err)
+	}
+	res := buf.Bytes()
+
+	// update golden files if necessary
+	if *update {
+		if err := ioutil.WriteFile(golden, res, 0644); err != nil {
+			t.Error(err)
+		}
+		return
+	}
+
+	// get golden
+	gld, err := ioutil.ReadFile(golden)
+	if err != nil {
+		t.Error(err)
+		return
+	}
+
+	// compare lengths
+	if len(res) != len(gld) {
+		t.Errorf("len = %d, expected %d (= len(%s))", len(res), len(gld), golden)
+	}
+
+	// compare contents
+	for i, line, offs := 0, 1, 0; i < len(res) && i < len(gld); i++ {
+		ch := res[i]
+		if ch != gld[i] {
+			t.Errorf("%s:%d:%d: %s", source, line, i-offs+1, lineString(res, offs))
+			t.Errorf("%s:%d:%d: %s", golden, line, i-offs+1, lineString(gld, offs))
+			t.Error()
+			return
+		}
+		if ch == '\n' {
+			line++
+			offs = i + 1
+		}
+	}
+}
+
+func check(t *testing.T, source, golden string, mode checkMode) {
+	// start a timer to produce a time-out signal
+	tc := make(chan int)
+	go func() {
+		time.Sleep(10e9) // plenty of a safety margin, even for very slow machines
+		tc <- 0
+	}()
+
+	// run the test
+	cc := make(chan int)
+	go func() {
+		runcheck(t, source, golden, mode)
+		cc <- 0
+	}()
+
+	// wait for the first finisher
+	select {
+	case <-tc:
+		// test running past time out
+		t.Errorf("%s: running too slowly", source)
+	case <-cc:
+		// test finished within alloted time margin
+	}
+}
+
+type entry struct {
+	source, golden string
+	mode           checkMode
+}
+
+// Use gotest -update to create/update the respective golden files.
+var data = []entry{
+	{"empty.input", "empty.golden", 0},
+	{"comments.input", "comments.golden", 0},
+	{"comments.input", "comments.x", export},
+	{"linebreaks.input", "linebreaks.golden", 0},
+	{"expressions.input", "expressions.golden", 0},
+	{"expressions.input", "expressions.raw", rawFormat},
+	{"declarations.input", "declarations.golden", 0},
+	{"statements.input", "statements.golden", 0},
+	{"slow.input", "slow.golden", 0},
+}
+
+func TestFiles(t *testing.T) {
+	for i, e := range data {
+		source := filepath.Join(dataDir, e.source)
+		golden := filepath.Join(dataDir, e.golden)
+		check(t, source, golden, e.mode)
+		// TODO(gri) check that golden is idempotent
+		//check(t, golden, golden, e.mode)
+		if testing.Short() && i >= 3 {
+			break
+		}
+	}
+}
+
+// TestLineComments, using a simple test case, checks that consequtive line
+// comments are properly terminated with a newline even if the AST position
+// information is incorrect.
+//
+func TestLineComments(t *testing.T) {
+	const src = `// comment 1
+	// comment 2
+	// comment 3
+	package main
+	`
+
+	fset := token.NewFileSet()
+	ast1, err1 := parser.ParseFile(fset, "", src, parser.ParseComments)
+	if err1 != nil {
+		panic(err1)
+	}
+
+	var buf bytes.Buffer
+	fset = token.NewFileSet() // use the wrong file set
+	Fprint(&buf, fset, ast1)
+
+	nlines := 0
+	for _, ch := range buf.Bytes() {
+		if ch == '\n' {
+			nlines++
+		}
+	}
+
+	const expected = 3
+	if nlines < expected {
+		t.Errorf("got %d, expected %d\n", nlines, expected)
+	}
+}
diff --git a/src/pkg/go/printer/testdata/comments.golden b/src/pkg/go/printer/testdata/comments.golden
new file mode 100644
index 000000000..7b332252c
--- /dev/null
+++ b/src/pkg/go/printer/testdata/comments.golden
@@ -0,0 +1,473 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This is a package for testing comment placement by go/printer.
+//
+package main
+
+import "fmt"	// fmt
+
+const c0 = 0	// zero
+const (
+	c1	= iota	// c1
+	c2		// c2
+)
+
+// Alignment of comments in declarations>
+const (
+	_	T	= iota	// comment
+	_			// comment
+	_			// comment
+	_	= iota + 10
+	_	// comments
+
+	_		= 10	// comment
+	_	T	= 20	// comment
+)
+
+const (
+	_____	= iota	// foo
+	_		// bar
+	_	= 0	// bal
+	_		// bat
+)
+
+const (
+	_	T	= iota	// comment
+	_			// comment
+	_			// comment
+	_	= iota + 10
+	_		// comment
+	_		= 10
+	_		= 20	// comment
+	_	T	= 0	// comment
+)
+
+// The SZ struct; it is empty.
+type SZ struct{}
+
+// The S0 struct; no field is exported.
+type S0 struct {
+	int
+	x, y, z	int	// 3 unexported fields
+}
+
+// The S1 struct; some fields are not exported.
+type S1 struct {
+	S0
+	A, B, C	float	// 3 exported fields
+	D, b, c	int	// 2 unexported fields
+}
+
+// The S2 struct; all fields are exported.
+type S2 struct {
+	S1
+	A, B, C	float	// 3 exported fields
+}
+
+// The IZ interface; it is empty.
+type SZ interface{}
+
+// The I0 interface; no method is exported.
+type I0 interface {
+	f(x int) int	// unexported method
+}
+
+// The I1 interface; some methods are not exported.
+type I1 interface {
+	I0
+	F(x float) float	// exported methods
+	g(x int) int		// unexported method
+}
+
+// The I2 interface; all methods are exported.
+type I2 interface {
+	I0
+	F(x float) float	// exported method
+	G(x float) float	// exported method
+}
+
+// The S3 struct; all comments except for the last one must appear in the export.
+type S3 struct {
+	// lead comment for F1
+	F1	int	// line comment for F1
+	// lead comment for F2
+	F2	int	// line comment for F2
+	f3	int	// f3 is not exported
+}
+
+// This comment group should be separated
+// with a newline from the next comment
+// group.
+
+// This comment should NOT be associated with the next declaration.
+
+var x int	// x
+var ()
+
+// This comment SHOULD be associated with the next declaration.
+func f0() {
+	const pi = 3.14	// pi
+	var s1 struct{}	/* an empty struct */	/* foo */
+	// a struct constructor
+	// --------------------
+	var s2 struct{} = struct{}{}
+	x := pi
+}
+//
+// NO SPACE HERE
+//
+func f1() {
+	f0()
+	/* 1 */
+	// 2
+	/* 3 */
+	/* 4 */
+	f0()
+}
+
+func _() {
+	// this comment should be properly indented
+}
+
+func _(x int) int {
+	if x < 0 {	// the tab printed before this comment's // must not affect the remaining lines
+		return -x	// this statement should be properly indented
+	}
+	if x < 0 {	/* the tab printed before this comment's /* must not affect the remaining lines */
+		return -x	// this statement should be properly indented
+	}
+	return x
+}
+
+func typeswitch(x interface{}) {
+	switch v := x.(type) {
+	case bool, int, float:
+	case string:
+	default:
+	}
+
+	switch x.(type) {
+	}
+
+	switch v0, ok := x.(int); v := x.(type) {
+	}
+
+	switch v0, ok := x.(int); x.(type) {
+	case byte:	// this comment should be on the same line as the keyword
+		// this comment should be normally indented
+		_ = 0
+	case bool, int, float:
+		// this comment should be indented
+	case string:
+	default:
+		// this comment should be indented
+	}
+	// this comment should not be indented
+}
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line */
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line */
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line */
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line */
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line */
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line */
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line */
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line */
+}
+
+/*
+ * line
+ * of
+ * stars
+ */
+
+/* another line
+ * of
+ * stars */
+
+/*	and another line
+ *	of
+ *	stars */
+
+/* a line of
+ * stars */
+
+/*	and another line of
+ *	stars */
+
+/* a line of stars
+ */
+
+/*	and another line of
+ */
+
+/* a line of stars
+ */
+
+/*	and another line of
+ */
+
+/*
+aligned in middle
+here
+        not here
+*/
+
+/*
+blank line in middle:
+
+with no leading spaces on blank line.
+*/
+
+/*
+   aligned in middle
+   here
+           not here
+*/
+
+/*
+	blank line in middle:
+
+	with no leading spaces on blank line.
+*/
+
+func _() {
+	/*
+	 * line
+	 * of
+	 * stars
+	 */
+
+	/*
+		aligned in middle
+		here
+			not here
+	*/
+
+	/*
+		blank line in middle:
+
+		with no leading spaces on blank line.
+	*/
+}
+
+// Some interesting interspersed comments
+func _( /* this */ x /* is */ /* an */ int) {
+}
+
+func _( /* no params */ )	{}
+
+func _() {
+	f( /* no args */ )
+}
+
+func ( /* comment1 */ T /* comment2 */ ) _()	{}
+
+func _() { /* one-line functions with comments are formatted as multi-line functions */
+}
+
+func _() {
+	_ = 0
+	/* closing curly brace should be on new line */
+}
+
+func _() {
+	_ = []int{0, 1 /* don't introduce a newline after this comment - was issue 1365 */ }
+}
+
+// Comments immediately adjacent to punctuation (for which the go/printer
+// may only have estimated position information) must remain after the punctuation.
+func _() {
+	_ = T{
+		1,	// comment after comma
+		2,	/* comment after comma */
+		3,	// comment after comma
+	}
+	_ = T{
+		1,	// comment after comma
+		2,	/* comment after comma */
+		3,	// comment after comma
+	}
+	_ = T{
+		/* comment before literal */ 1,
+		2,	/* comment before comma - ok to move after comma */
+		3,	/* comment before comma - ok to move after comma */
+	}
+
+	for i = 0;	// comment after semicolon
+	i < 9;		/* comment after semicolon */
+	i++ {		// comment after opening curly brace
+	}
+
+	// TODO(gri) the last comment in this example should be aligned */
+	for i = 0;	// comment after semicolon
+	i < 9;		/* comment before semicolon - ok to move after semicolon */
+	i++ /* comment before opening curly brace */ {
+	}
+}
+
+// Line comments with tabs
+func _() {
+	var finput *bufio.Reader	// input file
+	var stderr *bufio.Writer
+	var ftable *bufio.Writer	// y.go file
+	var foutput *bufio.Writer	// y.output file
+
+	var oflag string	// -o [y.go]		- y.go file
+	var vflag string	// -v [y.output]	- y.output file
+	var lflag bool		// -l			- disable line directives
+}
+
+/* This comment is the last entry in this file. It must be printed and should be followed by a newline */
diff --git a/src/pkg/go/printer/testdata/comments.input b/src/pkg/go/printer/testdata/comments.input
new file mode 100644
index 000000000..2a9a86b68
--- /dev/null
+++ b/src/pkg/go/printer/testdata/comments.input
@@ -0,0 +1,483 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This is a package for testing comment placement by go/printer.
+//
+package main
+
+import "fmt"  // fmt
+
+const c0 = 0  // zero
+const (
+	c1 = iota  // c1
+	c2  // c2
+)
+
+// Alignment of comments in declarations>
+const (
+	_ T = iota  // comment
+	_  // comment
+	_  // comment
+	_ = iota+10
+	_  // comments
+
+	_ = 10  // comment
+	_ T = 20  // comment
+)
+
+const (
+	_____ = iota // foo
+	_ // bar
+	_  = 0    // bal
+	_ // bat
+)
+
+const (
+	_ T = iota // comment
+	_ // comment
+	_ // comment
+	_ = iota + 10
+	_ // comment
+	_ = 10
+	_ = 20 // comment
+	_ T = 0 // comment
+)
+
+// The SZ struct; it is empty.
+type SZ struct {}
+
+// The S0 struct; no field is exported.
+type S0 struct {
+	int
+	x, y, z int  // 3 unexported fields
+}
+
+// The S1 struct; some fields are not exported.
+type S1 struct {
+	S0
+	A, B, C float  // 3 exported fields
+	D, b, c int  // 2 unexported fields
+}
+
+// The S2 struct; all fields are exported.
+type S2 struct {
+	S1
+	A, B, C float  // 3 exported fields
+}
+
+// The IZ interface; it is empty.
+type SZ interface {}
+
+// The I0 interface; no method is exported.
+type I0 interface {
+	f(x int) int  // unexported method
+}
+
+// The I1 interface; some methods are not exported.
+type I1 interface {
+	I0
+	F(x float) float  // exported methods
+	g(x int) int  // unexported method
+}
+
+// The I2 interface; all methods are exported.
+type I2 interface {
+	I0
+	F(x float) float  // exported method
+	G(x float) float  // exported method
+}
+
+// The S3 struct; all comments except for the last one must appear in the export.
+type S3 struct {
+	// lead comment for F1
+	F1 int // line comment for F1
+	// lead comment for F2
+	F2 int // line comment for F2
+	f3 int // f3 is not exported
+}
+
+// This comment group should be separated
+// with a newline from the next comment
+// group.
+
+// This comment should NOT be associated with the next declaration.
+
+var x int  // x
+var ()
+
+
+// This comment SHOULD be associated with the next declaration.
+func f0() {
+	const pi = 3.14  // pi
+	var s1 struct {}  /* an empty struct */ /* foo */
+	// a struct constructor
+	// --------------------
+	var s2 struct {} = struct {}{}
+	x := pi
+}
+//
+// NO SPACE HERE
+//
+func f1() {
+	f0()
+	/* 1 */
+	// 2
+	/* 3 */
+	/* 4 */
+	f0()
+}
+
+
+func _() {
+	// this comment should be properly indented
+}
+
+
+func _(x int) int {
+	if x < 0 {  // the tab printed before this comment's // must not affect the remaining lines
+		return -x  // this statement should be properly indented
+	}
+	if x < 0 {  /* the tab printed before this comment's /* must not affect the remaining lines */
+		return -x  // this statement should be properly indented
+	}
+	return x
+}
+
+
+func typeswitch(x interface{}) {
+	switch v := x.(type) {
+	case bool, int, float:
+	case string:
+	default:
+	}
+
+	switch x.(type) {
+	}
+
+	switch v0, ok := x.(int); v := x.(type) {
+	}
+
+	switch v0, ok := x.(int); x.(type) {
+	case byte:  // this comment should be on the same line as the keyword
+		// this comment should be normally indented
+		_ = 0
+	case bool, int, float:
+		// this comment should be indented
+	case string:
+	default:
+		// this comment should be indented
+	}
+	// this comment should not be indented
+}
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line
+	   */
+}
+
+func _() {
+	/* freestanding comment
+	   aligned		line
+	   aligned line */
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line
+		*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned		line
+		aligned line */
+}
+
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line
+	   */
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned		line
+	   aligned line */
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line
+		*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned		line
+		aligned line */
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line
+	   */
+}
+
+func _() {
+	/* freestanding comment
+	   aligned line */
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line
+		*/
+}
+
+func _() {
+	/*	freestanding comment
+		aligned line */
+}
+
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line
+	*/
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line
+	   */
+}
+
+func _() {
+	/*
+	   freestanding comment
+	   aligned line */
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line
+	*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line
+		*/
+}
+
+func _() {
+	/*
+		freestanding comment
+		aligned line */
+}
+
+/*
+ * line
+ * of
+ * stars
+ */
+
+/* another line
+ * of
+ * stars */
+
+/*	and another line
+ *	of
+ *	stars */
+
+/* a line of
+ * stars */
+
+/*	and another line of
+ *	stars */
+
+/* a line of stars
+*/
+
+/*	and another line of
+*/
+
+/* a line of stars
+ */
+
+/*	and another line of
+ */
+
+/*
+aligned in middle
+here
+        not here
+*/
+
+/*
+blank line in middle:
+
+with no leading spaces on blank line.
+*/
+
+/*
+   aligned in middle
+   here
+           not here
+*/
+
+/*
+	blank line in middle:
+
+	with no leading spaces on blank line.
+*/
+
+func _() {
+	/*
+	 * line
+	 * of
+	 * stars
+	 */
+
+	/*
+	aligned in middle
+	here
+		not here
+	*/
+
+	/*
+	blank line in middle:
+
+	with no leading spaces on blank line.
+*/
+}
+
+
+// Some interesting interspersed comments
+func _(/* this */x/* is *//* an */ int) {
+}
+
+func _(/* no params */) {}
+
+func _() {
+	f(/* no args */)
+}
+
+func (/* comment1 */ T /* comment2 */) _() {}
+
+func _() { /* one-line functions with comments are formatted as multi-line functions */ }
+
+func _() {
+	_ = 0
+	/* closing curly brace should be on new line */ }
+
+func _() {
+	_ = []int{0, 1 /* don't introduce a newline after this comment - was issue 1365 */}
+}
+
+
+// Comments immediately adjacent to punctuation (for which the go/printer
+// may only have estimated position information) must remain after the punctuation.
+func _() {
+	_ = T{
+		1,    // comment after comma
+		2,    /* comment after comma */
+		3  ,  // comment after comma
+	}
+	_ = T{
+		1  ,// comment after comma
+		2  ,/* comment after comma */
+		3,// comment after comma
+	}
+	_ = T{
+		/* comment before literal */1,
+		2/* comment before comma - ok to move after comma */,
+		3  /* comment before comma - ok to move after comma */  ,
+	}
+
+	for
+		i=0;// comment after semicolon
+		i<9;/* comment after semicolon */
+		i++{// comment after opening curly brace
+	}
+
+	// TODO(gri) the last comment in this example should be aligned */
+	for
+		i=0;// comment after semicolon
+		i<9/* comment before semicolon - ok to move after semicolon */;
+		i++ /* comment before opening curly brace */ {
+	}
+}
+
+
+// Line comments with tabs
+func _() {
+var	finput		*bufio.Reader			// input file
+var	stderr		*bufio.Writer
+var	ftable		*bufio.Writer			// y.go file
+var	foutput		*bufio.Writer			// y.output file
+
+var	oflag		string				// -o [y.go]		- y.go file
+var	vflag		string				// -v [y.output]	- y.output file
+var	lflag		bool				// -l			- disable line directives
+}
+
+
+/* This comment is the last entry in this file. It must be printed and should be followed by a newline */
diff --git a/src/pkg/go/printer/testdata/comments.x b/src/pkg/go/printer/testdata/comments.x
new file mode 100644
index 000000000..ae7729286
--- /dev/null
+++ b/src/pkg/go/printer/testdata/comments.x
@@ -0,0 +1,56 @@
+// This is a package for testing comment placement by go/printer.
+//
+package main
+
+// The SZ struct; it is empty.
+type SZ struct{}
+
+// The S0 struct; no field is exported.
+type S0 struct {
+	// contains filtered or unexported fields
+}
+
+// The S1 struct; some fields are not exported.
+type S1 struct {
+	S0
+	A, B, C	float	// 3 exported fields
+	D	int	// 2 unexported fields
+	// contains filtered or unexported fields
+}
+
+// The S2 struct; all fields are exported.
+type S2 struct {
+	S1
+	A, B, C	float	// 3 exported fields
+}
+
+// The IZ interface; it is empty.
+type SZ interface{}
+
+// The I0 interface; no method is exported.
+type I0 interface {
+	// contains filtered or unexported methods
+}
+
+// The I1 interface; some methods are not exported.
+type I1 interface {
+	I0
+	F(x float) float	// exported methods
+	// contains filtered or unexported methods
+}
+
+// The I2 interface; all methods are exported.
+type I2 interface {
+	I0
+	F(x float) float	// exported method
+	G(x float) float	// exported method
+}
+
+// The S3 struct; all comments except for the last one must appear in the export.
+type S3 struct {
+	// lead comment for F1
+	F1	int	// line comment for F1
+	// lead comment for F2
+	F2	int	// line comment for F2
+	// contains filtered or unexported fields
+}
diff --git a/src/pkg/go/printer/testdata/declarations.golden b/src/pkg/go/printer/testdata/declarations.golden
new file mode 100644
index 000000000..970533e8c
--- /dev/null
+++ b/src/pkg/go/printer/testdata/declarations.golden
@@ -0,0 +1,747 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package imports
+
+import "io"
+
+import (
+	_ "io"
+)
+
+import _ "io"
+
+import (
+	"io"
+	"io"
+	"io"
+)
+
+import (
+	"io"
+	aLongRename "io"
+
+	b "io"
+)
+
+import (
+	"unrenamed"
+	renamed "renameMe"
+	. "io"
+	_ "io"
+	"io"
+	. "os"
+)
+
+// no newlines between consecutive single imports, but
+// respect extra line breaks in the source (at most one empty line)
+import _ "io"
+import _ "io"
+import _ "io"
+
+import _ "os"
+import _ "os"
+import _ "os"
+
+import _ "fmt"
+import _ "fmt"
+import _ "fmt"
+
+import "foo"	// a comment
+import "bar"	// a comment
+
+import (
+	_ "foo"
+	// a comment
+	"bar"
+	"foo"	// a comment
+	"bar"	// a comment
+)
+
+// comments + renames
+import (
+	"unrenamed"	// a comment
+	renamed "renameMe"
+	. "io"		/* a comment */
+	_ "io/ioutil"	// a comment
+	"io"		// testing alignment
+	. "os"
+	// a comment
+)
+
+// a case that caused problems in the past (comment placement)
+import (
+	. "fmt"
+	"io"
+	"malloc"	// for the malloc count test only
+	"math"
+	"strings"
+	"testing"
+)
+
+// more import examples
+import (
+	"xxx"
+	"much longer name"	// comment
+	"short name"		// comment
+)
+
+import (
+	_ "xxx"
+	"much longer name"	// comment
+)
+
+import (
+	mymath "math"
+	"/foo/bar/long_package_path"	// a comment
+)
+
+import (
+	"package_a"	// comment
+	"package_b"
+	my_better_c "package_c"	// comment
+	"package_d"		// comment
+	my_e "package_e"	// comment
+
+	"package_a"	// comment
+	"package_bb"
+	"package_ccc"	// comment
+	"package_dddd"	// comment
+)
+
+// at least one empty line between declarations of different kind
+import _ "io"
+
+var _ int
+
+// printing of constant literals
+const (
+	_	= "foobar"
+	_	= "a۰۱۸"
+	_	= "foo६४"
+	_	= "bar９８７６"
+	_	= 0
+	_	= 1
+	_	= 123456789012345678890
+	_	= 01234567
+	_	= 0xcafebabe
+	_	= 0.
+	_	= .0
+	_	= 3.14159265
+	_	= 1e0
+	_	= 1e+100
+	_	= 1e-100
+	_	= 2.71828e-1000
+	_	= 0i
+	_	= 1i
+	_	= 012345678901234567889i
+	_	= 123456789012345678890i
+	_	= 0.i
+	_	= .0i
+	_	= 3.14159265i
+	_	= 1e0i
+	_	= 1e+100i
+	_	= 1e-100i
+	_	= 2.71828e-1000i
+	_	= 'a'
+	_	= '\000'
+	_	= '\xFF'
+	_	= '\uff16'
+	_	= '\U0000ff16'
+	_	= `foobar`
+	_	= `foo
+---
+---
+bar`
+)
+
+func _() {
+	type _ int
+	type _ *int
+	type _ []int
+	type _ map[string]int
+	type _ chan int
+	type _ func() int
+
+	var _ int
+	var _ *int
+	var _ []int
+	var _ map[string]int
+	var _ chan int
+	var _ func() int
+
+	type _ struct{}
+	type _ *struct{}
+	type _ []struct{}
+	type _ map[string]struct{}
+	type _ chan struct{}
+	type _ func() struct{}
+
+	type _ interface{}
+	type _ *interface{}
+	type _ []interface{}
+	type _ map[string]interface{}
+	type _ chan interface{}
+	type _ func() interface{}
+
+	var _ struct{}
+	var _ *struct{}
+	var _ []struct{}
+	var _ map[string]struct{}
+	var _ chan struct{}
+	var _ func() struct{}
+
+	var _ interface{}
+	var _ *interface{}
+	var _ []interface{}
+	var _ map[string]interface{}
+	var _ chan interface{}
+	var _ func() interface{}
+}
+
+// don't lose blank lines in grouped declarations
+const (
+	_	int	= 0
+	_	float	= 1
+
+	_	string	= "foo"
+
+	_	= iota
+	_
+
+	// a comment
+	_
+
+	_
+)
+
+type (
+	_	int
+	_	struct{}
+
+	_	interface{}
+
+	// a comment
+	_	map[string]int
+)
+
+var (
+	_	int	= 0
+	_	float	= 1
+
+	_	string	= "foo"
+
+	_	bool
+
+	// a comment
+	_	bool
+)
+
+// don't lose blank lines in this struct
+type _ struct {
+	String	struct {
+		Str, Len int
+	}
+	Slice	struct {
+		Array, Len, Cap int
+	}
+	Eface	struct {
+		Typ, Ptr int
+	}
+
+	UncommonType	struct {
+		Name, PkgPath int
+	}
+	CommonType	struct {
+		Size, Hash, Alg, Align, FieldAlign, String, UncommonType int
+	}
+	Type	struct {
+		Typ, Ptr int
+	}
+	StructField	struct {
+		Name, PkgPath, Typ, Tag, Offset int
+	}
+	StructType	struct {
+		Fields int
+	}
+	PtrType	struct {
+		Elem int
+	}
+	SliceType	struct {
+		Elem int
+	}
+	ArrayType	struct {
+		Elem, Len int
+	}
+
+	Stktop	struct {
+		Stackguard, Stackbase, Gobuf int
+	}
+	Gobuf	struct {
+		Sp, Pc, G int
+	}
+	G	struct {
+		Stackbase, Sched, Status, Alllink int
+	}
+}
+
+// no tabs for single or ungrouped decls
+func _() {
+	const xxxxxx = 0
+	type x int
+	var xxx int
+	var yyyy float = 3.14
+	var zzzzz = "bar"
+
+	const (
+		xxxxxx = 0
+	)
+	type (
+		x int
+	)
+	var (
+		xxx int
+	)
+	var (
+		yyyy float = 3.14
+	)
+	var (
+		zzzzz = "bar"
+	)
+}
+
+// tabs for multiple or grouped decls
+func _() {
+	// no entry has a type
+	const (
+		zzzzzz	= 1
+		z	= 2
+		zzz	= 3
+	)
+	// some entries have a type
+	const (
+		xxxxxx			= 1
+		x			= 2
+		xxx			= 3
+		yyyyyyyy	float	= iota
+		yyyy			= "bar"
+		yyy
+		yy	= 2
+	)
+}
+
+func _() {
+	// no entry has a type
+	var (
+		zzzzzz	= 1
+		z	= 2
+		zzz	= 3
+	)
+	// no entry has a value
+	var (
+		_	int
+		_	float
+		_	string
+
+		_	int	// comment
+		_	float	// comment
+		_	string	// comment
+	)
+	// some entries have a type
+	var (
+		xxxxxx		int
+		x		float
+		xxx		string
+		yyyyyyyy	int	= 1234
+		y		float	= 3.14
+		yyyy			= "bar"
+		yyy		string	= "foo"
+	)
+	// mixed entries - all comments should be aligned
+	var (
+		a, b, c			int
+		x			= 10
+		d			int			// comment
+		y				= 20		// comment
+		f, ff, fff, ffff	int	= 0, 1, 2, 3	// comment
+	)
+	// respect original line breaks
+	var _ = []T{
+		T{0x20, "Telugu"},
+	}
+	var _ = []T{
+		// respect original line breaks
+		T{0x20, "Telugu"},
+	}
+}
+
+func _() {
+	type (
+		xxxxxx	int
+		x	float
+		xxx	string
+		xxxxx	[]x
+		xx	struct{}
+		xxxxxxx	struct {
+			_, _	int
+			_	float
+		}
+		xxxx	chan<- string
+	)
+}
+
+// alignment of "=" in consecutive lines (extended example from issue 1414)
+const (
+	umax	uint	= ^uint(0)		// maximum value for a uint
+	bpu		= 1 << (5 + umax>>63)	// bits per uint
+	foo
+	bar	= -1
+)
+
+// typical enum
+const (
+	a	MyType	= iota
+	abcd
+	b
+	c
+	def
+)
+
+// excerpt from godoc.go
+var (
+	goroot		= flag.String("goroot", runtime.GOROOT(), "Go root directory")
+	testDir		= flag.String("testdir", "", "Go root subdirectory - for testing only (faster startups)")
+	pkgPath		= flag.String("path", "", "additional package directories (colon-separated)")
+	filter		= flag.String("filter", "", "filter file containing permitted package directory paths")
+	filterMin	= flag.Int("filter_minutes", 0, "filter file update interval in minutes; disabled if <= 0")
+	filterDelay	delayTime	// actual filter update interval in minutes; usually filterDelay == filterMin, but filterDelay may back off exponentially
+)
+
+// formatting of structs
+type _ struct{}
+
+type _ struct { /* this comment should be visible */
+}
+
+type _ struct {
+	// this comment should be visible and properly indented
+}
+
+type _ struct {	// this comment must not change indentation
+	f			int
+	f, ff, fff, ffff	int
+}
+
+type _ struct {
+	string
+}
+
+type _ struct {
+	string	// comment
+}
+
+type _ struct {
+	string "tag"
+}
+
+type _ struct {
+	string "tag"	// comment
+}
+
+type _ struct {
+	f int
+}
+
+type _ struct {
+	f int	// comment
+}
+
+type _ struct {
+	f int "tag"
+}
+
+type _ struct {
+	f int "tag"	// comment
+}
+
+type _ struct {
+	bool
+	a, b, c			int
+	int			"tag"
+	ES				// comment
+	float			"tag"	// comment
+	f			int	// comment
+	f, ff, fff, ffff	int	// comment
+	g			float	"tag"
+	h			float	"tag"	// comment
+}
+
+type _ struct {
+	a, b,
+	c, d	int	// this line should be indented
+	u, v, w, x	float	// this line should be indented
+	p, q,
+	r, s	float	// this line should be indented
+}
+
+// difficult cases
+type _ struct {
+	bool		// comment
+	text	[]byte	// comment
+}
+
+// formatting of interfaces
+type EI interface{}
+
+type _ interface {
+	EI
+}
+
+type _ interface {
+	f()
+	fffff()
+}
+
+type _ interface {
+	EI
+	f()
+	fffffg()
+}
+
+type _ interface {	// this comment must not change indentation
+	EI				// here's a comment
+	f()				// no blank between identifier and ()
+	fffff()				// no blank between identifier and ()
+	gggggggggggg(x, y, z int)	// hurray
+}
+
+// formatting of variable declarations
+func _() {
+	type day struct {
+		n		int
+		short, long	string
+	}
+	var (
+		Sunday		= day{0, "SUN", "Sunday"}
+		Monday		= day{1, "MON", "Monday"}
+		Tuesday		= day{2, "TUE", "Tuesday"}
+		Wednesday	= day{3, "WED", "Wednesday"}
+		Thursday	= day{4, "THU", "Thursday"}
+		Friday		= day{5, "FRI", "Friday"}
+		Saturday	= day{6, "SAT", "Saturday"}
+	)
+}
+
+// formatting of multi-line variable declarations
+var a1, b1, c1 int	// all on one line
+
+var a2, b2,
+	c2 int	// this line should be indented
+
+var (
+	a3, b3,
+	c3, d3	int	// this line should be indented
+	a4, b4, c4	int	// this line should be indented
+)
+
+func _() {
+	var privateKey2 = &Block{Type:	"RSA PRIVATE KEY",
+		Headers:	map[string]string{},
+		Bytes: []uint8{0x30, 0x82, 0x1, 0x3a, 0x2, 0x1, 0x0, 0x2,
+			0x41, 0x0, 0xb2, 0x99, 0xf, 0x49, 0xc4, 0x7d, 0xfa, 0x8c,
+			0xd4, 0x0, 0xae, 0x6a, 0x4d, 0x1b, 0x8a, 0x3b, 0x6a, 0x13,
+			0x64, 0x2b, 0x23, 0xf2, 0x8b, 0x0, 0x3b, 0xfb, 0x97, 0x79,
+		},
+	}
+}
+
+func _() {
+	var Universe = Scope{
+		Names: map[string]*Ident{
+			// basic types
+			"bool":		nil,
+			"byte":		nil,
+			"int8":		nil,
+			"int16":	nil,
+			"int32":	nil,
+			"int64":	nil,
+			"uint8":	nil,
+			"uint16":	nil,
+			"uint32":	nil,
+			"uint64":	nil,
+			"float32":	nil,
+			"float64":	nil,
+			"string":	nil,
+
+			// convenience types
+			"int":		nil,
+			"uint":		nil,
+			"uintptr":	nil,
+			"float":	nil,
+
+			// constants
+			"false":	nil,
+			"true":		nil,
+			"iota":		nil,
+			"nil":		nil,
+
+			// functions
+			"cap":		nil,
+			"len":		nil,
+			"new":		nil,
+			"make":		nil,
+			"panic":	nil,
+			"panicln":	nil,
+			"print":	nil,
+			"println":	nil,
+		},
+	}
+}
+
+// alignment of map composite entries
+var _ = map[int]int{
+	// small key sizes: always align even if size ratios are large
+	a:			a,
+	abcdefghabcdefgh:	a,
+	ab:			a,
+	abc:			a,
+	abcdefgabcdefg:		a,
+	abcd:			a,
+	abcde:			a,
+	abcdef:			a,
+
+	// mixed key sizes: align when key sizes change within accepted ratio
+	abcdefgh:		a,
+	abcdefghabcdefg:	a,
+	abcdefghij:		a,
+	abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghij:	a,	// outlier - do not align with previous line
+	abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghij:		a,	// align with previous line
+
+	ab:	a,	// do not align with previous line
+	abcde:	a,	// align with previous line
+}
+
+func _() {
+	var _ = T{
+		a,	// must introduce trailing comma
+	}
+}
+
+// formatting of function results
+func _() func()				{}
+func _() func(int)			{ return nil }
+func _() func(int) int			{ return nil }
+func _() func(int) func(int) func()	{ return nil }
+
+// formatting of consecutive single-line functions
+func _()	{}
+func _()	{}
+func _()	{}
+
+func _()	{}	// an empty line before this function
+func _()	{}
+func _()	{}
+
+func _()		{ f(1, 2, 3) }
+func _(x int) int	{ y := x; return y + 1 }
+func _() int		{ type T struct{}; var x T; return x }
+
+// these must remain multi-line since they are multi-line in the source
+func _() {
+	f(1, 2, 3)
+}
+func _(x int) int {
+	y := x
+	return y + 1
+}
+func _() int {
+	type T struct{}
+	var x T
+	return x
+}
+
+// making function declarations safe for new semicolon rules
+func _() { /* multi-line func because of comment */
+}
+
+func _() {
+	/* multi-line func because block is on multiple lines */
+}
+
+// ellipsis parameters
+func _(...int)
+func _(...*int)
+func _(...[]int)
+func _(...struct{})
+func _(bool, ...interface{})
+func _(bool, ...func())
+func _(bool, ...func(...int))
+func _(bool, ...map[string]int)
+func _(bool, ...chan int)
+
+func _(b bool, x ...int)
+func _(b bool, x ...*int)
+func _(b bool, x ...[]int)
+func _(b bool, x ...struct{})
+func _(x ...interface{})
+func _(x ...func())
+func _(x ...func(...int))
+func _(x ...map[string]int)
+func _(x ...chan int)
+
+// these parameter lists must remain multi-line since they are multi-line in the source
+func _(bool,
+int) {
+}
+func _(x bool,
+y int) {
+}
+func _(x,
+y bool) {
+}
+func _(bool,	// comment
+int) {
+}
+func _(x bool,	// comment
+y int) {
+}
+func _(x,	// comment
+y bool) {
+}
+func _(bool,	// comment
+// comment
+int) {
+}
+func _(x bool,	// comment
+// comment
+y int) {
+}
+func _(x,	// comment
+// comment
+y bool) {
+}
+func _(bool,
+// comment
+int) {
+}
+func _(x bool,
+// comment
+y int) {
+}
+func _(x,
+// comment
+y bool) {
+}
+func _(x,	// comment
+y,	// comment
+z bool) {
+}
+func _(x,	// comment
+y,	// comment
+z bool) {
+}
+func _(x int,	// comment
+y float,	// comment
+z bool) {
+}
diff --git a/src/pkg/go/printer/testdata/declarations.input b/src/pkg/go/printer/testdata/declarations.input
new file mode 100644
index 000000000..c6134096b
--- /dev/null
+++ b/src/pkg/go/printer/testdata/declarations.input
@@ -0,0 +1,757 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package imports
+
+import "io"
+
+import (
+	_ "io"
+)
+
+import _ "io"
+
+import (
+	"io"
+	"io"
+	"io"
+)
+
+import (
+	"io"
+	aLongRename "io"
+
+	b "io"
+)
+
+import (
+       "unrenamed"
+       renamed "renameMe"
+       . "io"
+       _ "io"
+       "io"
+       . "os"
+)
+
+// no newlines between consecutive single imports, but
+// respect extra line breaks in the source (at most one empty line)
+import _ "io"
+import _ "io"
+import _ "io"
+
+import _ "os"
+import _ "os"
+import _ "os"
+
+
+import _ "fmt"
+import _ "fmt"
+import _ "fmt"
+
+import "foo"  // a comment
+import "bar"  // a comment
+
+import (
+	_ "foo"
+	// a comment
+	"bar"
+	"foo"  // a comment
+	"bar"  // a comment
+)
+
+// comments + renames
+import (
+       "unrenamed" // a comment
+       renamed "renameMe"
+       . "io" /* a comment */
+       _ "io/ioutil" // a comment
+       "io" // testing alignment
+       . "os"
+       // a comment
+)
+
+// a case that caused problems in the past (comment placement)
+import (
+	. "fmt"
+	"io"
+	"malloc"	// for the malloc count test only
+	"math"
+	"strings"
+	"testing"
+)
+
+// more import examples
+import (
+	"xxx"
+	"much longer name" // comment
+	"short name" // comment
+)
+
+import (
+	_ "xxx"
+	"much longer name" // comment
+)
+
+import (
+	mymath "math"
+	"/foo/bar/long_package_path" // a comment
+)
+
+import (
+	"package_a" // comment
+	"package_b"
+	my_better_c "package_c" // comment
+	"package_d" // comment
+	my_e "package_e" // comment
+
+	"package_a"    // comment
+	"package_bb"
+	"package_ccc"  // comment
+	"package_dddd" // comment
+)
+
+// at least one empty line between declarations of different kind
+import _ "io"
+var _ int
+
+
+// printing of constant literals
+const (
+	_ = "foobar"
+	_ = "a۰۱۸"
+	_ = "foo६४"
+	_ = "bar９８７６"
+	_ = 0
+	_ = 1
+	_ = 123456789012345678890
+	_ = 01234567
+	_ = 0xcafebabe
+	_ = 0.
+	_ = .0
+	_ = 3.14159265
+	_ = 1e0
+	_ = 1e+100
+	_ = 1e-100
+	_ = 2.71828e-1000
+	_ = 0i
+	_ = 1i
+	_ = 012345678901234567889i
+	_ = 123456789012345678890i
+	_ = 0.i
+	_ = .0i
+	_ = 3.14159265i
+	_ = 1e0i
+	_ = 1e+100i
+	_ = 1e-100i
+	_ = 2.71828e-1000i
+	_ = 'a'
+	_ = '\000'
+	_ = '\xFF'
+	_ = '\uff16'
+	_ = '\U0000ff16'
+	_ = `foobar`
+	_ = `foo
+---
+---
+bar`
+)
+
+
+func _() {
+	type _ int
+	type _ *int
+	type _ []int
+	type _ map[string]int
+	type _ chan int
+	type _ func() int
+
+	var _ int
+	var _ *int
+	var _ []int
+	var _ map[string]int
+	var _ chan int
+	var _ func() int
+
+	type _ struct{}
+	type _ *struct{}
+	type _ []struct{}
+	type _ map[string]struct{}
+	type _ chan struct{}
+	type _ func() struct{}
+
+	type _ interface{}
+	type _ *interface{}
+	type _ []interface{}
+	type _ map[string]interface{}
+	type _ chan interface{}
+	type _ func() interface{}
+
+	var _ struct{}
+	var _ *struct{}
+	var _ []struct{}
+	var _ map[string]struct{}
+	var _ chan struct{}
+	var _ func() struct{}
+
+	var _ interface{}
+	var _ *interface{}
+	var _ []interface{}
+	var _ map[string]interface{}
+	var _ chan interface{}
+	var _ func() interface{}
+}
+
+
+// don't lose blank lines in grouped declarations
+const (
+	_ int = 0
+	_ float = 1
+
+	_ string = "foo"
+
+	_ = iota
+	_
+	
+	// a comment
+	_
+
+	_
+)
+
+
+type (
+	_ int
+	_ struct {}
+	
+	_ interface{}
+	
+	// a comment
+	_ map[string]int
+)
+
+
+var (
+	_ int = 0
+	_ float = 1
+
+	_ string = "foo"
+
+	_ bool
+	
+	// a comment
+	_ bool
+)
+
+
+// don't lose blank lines in this struct
+type _ struct {
+	String struct {
+		Str, Len int
+	}
+	Slice struct {
+		Array, Len, Cap int
+	}
+	Eface struct {
+		Typ, Ptr int
+	}
+
+	UncommonType struct {
+		Name, PkgPath int
+	}
+	CommonType struct {
+		Size, Hash, Alg, Align, FieldAlign, String, UncommonType int
+	}
+	Type struct {
+		Typ, Ptr int
+	}
+	StructField struct {
+		Name, PkgPath, Typ, Tag, Offset int
+	}
+	StructType struct {
+		Fields int
+	}
+	PtrType struct {
+		Elem int
+	}
+	SliceType struct {
+		Elem int
+	}
+	ArrayType struct {
+		Elem, Len int
+	}
+
+	Stktop struct {
+		Stackguard, Stackbase, Gobuf int
+	}
+	Gobuf struct {
+		Sp, Pc, G int
+	}
+	G struct {
+		Stackbase, Sched, Status, Alllink int
+	}
+}
+
+
+// no tabs for single or ungrouped decls
+func _() {
+	const xxxxxx = 0
+	type x int
+	var xxx int
+	var yyyy float = 3.14
+	var zzzzz = "bar"
+
+	const (
+		xxxxxx = 0
+	)
+	type (
+		x int
+	)
+	var (
+		xxx int
+	)
+	var (
+		yyyy float = 3.14
+	)
+	var (
+		zzzzz = "bar"
+	)
+}
+
+// tabs for multiple or grouped decls
+func _() {
+	// no entry has a type
+	const (
+		zzzzzz = 1
+		z = 2
+		zzz = 3
+	)
+	// some entries have a type
+	const (
+		xxxxxx = 1
+		x = 2
+		xxx = 3
+		yyyyyyyy float = iota
+		yyyy = "bar"
+		yyy
+		yy = 2
+	)
+}
+
+func _() {
+	// no entry has a type
+	var (
+		zzzzzz = 1
+		z = 2
+		zzz = 3
+	)
+	// no entry has a value
+	var (
+		_ int
+		_ float
+		_ string
+
+		_ int  // comment
+		_ float  // comment
+		_ string  // comment
+	)
+	// some entries have a type
+	var (
+		xxxxxx int
+		x float
+		xxx string
+		yyyyyyyy int = 1234
+		y float = 3.14
+		yyyy = "bar"
+		yyy string = "foo"
+	)
+	// mixed entries - all comments should be aligned
+	var (
+		a, b, c int
+		x = 10
+		d int  // comment
+		y = 20  // comment
+		f, ff, fff, ffff int = 0, 1, 2, 3  // comment
+	)
+	// respect original line breaks
+	var _ = []T {
+		T{0x20,	"Telugu"},
+	}
+	var _ = []T {
+		// respect original line breaks
+		T{0x20,	"Telugu"},
+	}
+}
+
+func _() {
+	type (
+		xxxxxx int
+		x float
+		xxx string
+		xxxxx []x
+		xx struct{}
+		xxxxxxx struct {
+			_, _ int
+			_ float
+		}
+		xxxx chan<- string
+	)
+}
+
+// alignment of "=" in consecutive lines (extended example from issue 1414)
+const (
+	umax uint                  = ^uint(0) // maximum value for a uint
+	bpu  = 1 << (5 + umax>>63)            // bits per uint
+	foo
+	bar  = -1
+)
+
+// typical enum
+const (
+	a MyType = iota
+	abcd
+	b
+	c
+	def
+)
+
+// excerpt from godoc.go
+var (
+	goroot = flag.String("goroot", runtime.GOROOT(), "Go root directory")
+	testDir = flag.String("testdir", "", "Go root subdirectory - for testing only (faster startups)")
+	pkgPath = flag.String("path", "", "additional package directories (colon-separated)")
+	filter = flag.String("filter", "", "filter file containing permitted package directory paths")
+	filterMin = flag.Int("filter_minutes", 0, "filter file update interval in minutes; disabled if <= 0")
+	filterDelay delayTime // actual filter update interval in minutes; usually filterDelay == filterMin, but filterDelay may back off exponentially
+)
+
+
+// formatting of structs
+type _ struct{}
+
+type _ struct{ /* this comment should be visible */ }
+
+type _ struct{
+	// this comment should be visible and properly indented
+}
+
+type _ struct {  // this comment must not change indentation
+	f int
+	f, ff, fff, ffff int
+}
+
+type _ struct {
+	string
+}
+
+type _ struct {
+	string  // comment
+}
+
+type _ struct {
+	string "tag"
+}
+
+type _ struct {
+	string "tag"  // comment
+}
+
+type _ struct {
+	f int
+}
+
+type _ struct {
+	f int  // comment
+}
+
+type _ struct {
+	f int "tag"
+}
+
+type _ struct {
+	f int "tag"  // comment
+}
+
+type _ struct {
+	bool
+	a, b, c int
+	int "tag"
+	ES // comment
+	float "tag"  // comment
+	f int  // comment
+	f, ff, fff, ffff int  // comment
+	g float "tag"
+	h float "tag"  // comment
+}
+
+type _ struct { a, b,
+c, d int  // this line should be indented
+u, v, w, x float // this line should be indented
+p, q,
+r, s float // this line should be indented
+}
+
+
+// difficult cases
+type _ struct {
+	bool  // comment
+	text []byte  // comment
+}
+
+
+// formatting of interfaces
+type EI interface{}
+
+type _ interface {
+	EI
+}
+
+type _ interface {
+	f()
+	fffff()
+}
+
+type _ interface {
+	EI
+	f()
+	fffffg()
+}
+
+type _ interface {  // this comment must not change indentation
+	EI  // here's a comment
+	f()  // no blank between identifier and ()
+	fffff()  // no blank between identifier and ()
+	gggggggggggg(x, y, z int) ()  // hurray
+}
+
+
+// formatting of variable declarations
+func _() {
+	type day struct { n int; short, long string }
+	var (
+		Sunday = day{ 0, "SUN", "Sunday" }
+		Monday = day{ 1, "MON", "Monday" }
+		Tuesday = day{ 2, "TUE", "Tuesday" }
+		Wednesday = day{ 3, "WED", "Wednesday" }
+		Thursday = day{ 4, "THU", "Thursday" }
+		Friday = day{ 5, "FRI", "Friday" }
+		Saturday = day{ 6, "SAT", "Saturday" }
+	)
+}
+
+
+// formatting of multi-line variable declarations
+var a1, b1, c1 int  // all on one line
+
+var a2, b2,
+c2 int  // this line should be indented
+
+var (a3, b3,
+c3, d3 int  // this line should be indented
+a4, b4, c4 int  // this line should be indented
+)
+
+
+func _() {
+	var privateKey2 = &Block{Type: "RSA PRIVATE KEY",
+					Headers: map[string]string{},
+					Bytes: []uint8{0x30, 0x82, 0x1, 0x3a, 0x2, 0x1, 0x0, 0x2,
+			0x41, 0x0, 0xb2, 0x99, 0xf, 0x49, 0xc4, 0x7d, 0xfa, 0x8c,
+			0xd4, 0x0, 0xae, 0x6a, 0x4d, 0x1b, 0x8a, 0x3b, 0x6a, 0x13,
+			0x64, 0x2b, 0x23, 0xf2, 0x8b, 0x0, 0x3b, 0xfb, 0x97, 0x79,
+		},
+	}
+}
+
+
+func _() {
+	var Universe = Scope {
+		Names: map[string]*Ident {
+			// basic types
+			"bool": nil,
+			"byte": nil,
+			"int8": nil,
+			"int16": nil,
+			"int32": nil,
+			"int64": nil,
+			"uint8": nil,
+			"uint16": nil,
+			"uint32": nil,
+			"uint64": nil,
+			"float32": nil,
+			"float64": nil,
+			"string": nil,
+
+			// convenience types
+			"int": nil,
+			"uint": nil,
+			"uintptr": nil,
+			"float": nil,
+
+			// constants
+			"false": nil,
+			"true": nil,
+			"iota": nil,
+			"nil": nil,
+
+			// functions
+			"cap": nil,
+			"len": nil,
+			"new": nil,
+			"make": nil,
+			"panic": nil,
+			"panicln": nil,
+			"print": nil,
+			"println": nil,
+		},
+	}
+}
+
+
+// alignment of map composite entries
+var _ = map[int]int{
+	// small key sizes: always align even if size ratios are large
+	a: a,
+	abcdefghabcdefgh: a,
+	ab: a,
+	abc: a,
+	abcdefgabcdefg: a,
+	abcd: a,
+	abcde: a,
+	abcdef: a,
+
+	// mixed key sizes: align when key sizes change within accepted ratio
+	abcdefgh: a,
+	abcdefghabcdefg: a,
+	abcdefghij: a,
+	abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghij: a, // outlier - do not align with previous line
+	abcdefghijabcdefghijabcdefghijabcdefghijabcdefghijabcdefghij: a, // align with previous line
+
+	ab: a, // do not align with previous line
+	abcde: a, // align with previous line
+}
+
+
+func _() {
+	var _ = T{
+		a,	// must introduce trailing comma
+	}
+}
+
+
+// formatting of function results
+func _() func() {}
+func _() func(int) { return nil }
+func _() func(int) int { return nil }
+func _() func(int) func(int) func() { return nil }
+
+
+// formatting of consecutive single-line functions
+func _() {}
+func _() {}
+func _() {}
+
+func _() {}  // an empty line before this function
+func _() {}
+func _() {}
+
+func _() { f(1, 2, 3) }
+func _(x int) int { y := x; return y+1 }
+func _() int { type T struct{}; var x T; return x }
+
+// these must remain multi-line since they are multi-line in the source
+func _() {
+	f(1, 2, 3)
+}
+func _(x int) int {
+	y := x; return y+1
+}
+func _() int {
+	type T struct{}; var x T; return x
+}
+
+
+// making function declarations safe for new semicolon rules
+func _() { /* multi-line func because of comment */ }
+
+func _() {
+/* multi-line func because block is on multiple lines */ }
+
+
+// ellipsis parameters
+func _(...int)
+func _(...*int)
+func _(...[]int)
+func _(...struct{})
+func _(bool, ...interface{})
+func _(bool, ...func())
+func _(bool, ...func(...int))
+func _(bool, ...map[string]int)
+func _(bool, ...chan int)
+
+func _(b bool, x ...int)
+func _(b bool, x ...*int)
+func _(b bool, x ...[]int)
+func _(b bool, x ...struct{})
+func _(x ...interface{})
+func _(x ...func())
+func _(x ...func(...int))
+func _(x ...map[string]int)
+func _(x ...chan int)
+
+
+// these parameter lists must remain multi-line since they are multi-line in the source
+func _(bool,
+int) {
+}
+func _(x bool,
+y int) {
+}
+func _(x,
+y bool) {
+}
+func _(bool, // comment
+int) {
+}
+func _(x bool, // comment
+y int) {
+}
+func _(x, // comment
+y bool) {
+}
+func _(bool, // comment
+// comment
+int) {
+}
+func _(x bool, // comment
+// comment
+y int) {
+}
+func _(x, // comment
+// comment
+y bool) {
+}
+func _(bool,
+// comment
+int) {
+}
+func _(x bool,
+// comment
+y int) {
+}
+func _(x,
+// comment
+y bool) {
+}
+func _(x, // comment
+y,// comment
+z bool) {
+}
+func _(x, // comment
+	y,// comment
+	z bool) {
+}
+func _(x int,	// comment
+	y float,	// comment
+	z bool) {
+}
diff --git a/src/pkg/go/printer/testdata/empty.golden b/src/pkg/go/printer/testdata/empty.golden
new file mode 100644
index 000000000..a055f4758
--- /dev/null
+++ b/src/pkg/go/printer/testdata/empty.golden
@@ -0,0 +1,5 @@
+// a comment at the beginning of the file
+
+package empty
+
+// a comment at the end of the file
diff --git a/src/pkg/go/printer/testdata/empty.input b/src/pkg/go/printer/testdata/empty.input
new file mode 100644
index 000000000..a055f4758
--- /dev/null
+++ b/src/pkg/go/printer/testdata/empty.input
@@ -0,0 +1,5 @@
+// a comment at the beginning of the file
+
+package empty
+
+// a comment at the end of the file
diff --git a/src/pkg/go/printer/testdata/expressions.golden b/src/pkg/go/printer/testdata/expressions.golden
new file mode 100644
index 000000000..d0cf24ad6
--- /dev/null
+++ b/src/pkg/go/printer/testdata/expressions.golden
@@ -0,0 +1,627 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package expressions
+
+type T struct {
+	x, y, z int
+}
+
+var (
+	a, b, c, d, e						int
+	under_bar						int
+	longIdentifier1, longIdentifier2, longIdentifier3	int
+	t0, t1, t2						T
+	s							string
+	p							*int
+)
+
+func _() {
+	// no spaces around simple or parenthesized expressions
+	_ = (a + 0)
+	_ = a + b
+	_ = a + b + c
+	_ = a + b - c
+	_ = a - b - c
+	_ = a + (b * c)
+	_ = a + (b / c)
+	_ = a - (b % c)
+	_ = 1 + a
+	_ = a + 1
+	_ = a + b + 1
+	_ = s[a]
+	_ = s[a:]
+	_ = s[:b]
+	_ = s[1:2]
+	_ = s[a:b]
+	_ = s[0:len(s)]
+	_ = s[0] << 1
+	_ = (s[0] << 1) & 0xf
+	_ = s[0]<<2 | s[1]>>4
+	_ = "foo" + s
+	_ = s + "foo"
+	_ = 'a' + 'b'
+	_ = len(s) / 2
+	_ = len(t0.x) / a
+
+	// spaces around expressions of different precedence or expressions containing spaces
+	_ = a + -b
+	_ = a - ^b
+	_ = a / *p
+	_ = a + b*c
+	_ = 1 + b*c
+	_ = a + 2*c
+	_ = a + c*2
+	_ = 1 + 2*3
+	_ = s[1 : 2*3]
+	_ = s[a : b-c]
+	_ = s[0:]
+	_ = s[a+b]
+	_ = s[:b-c]
+	_ = s[a+b:]
+	_ = a[a<<b+1]
+	_ = a[a<<b+1:]
+	_ = s[a+b : len(s)]
+	_ = s[len(s):-a]
+	_ = s[a : len(s)+1]
+	_ = s[a:len(s)+1] + s
+
+	// spaces around operators with equal or lower precedence than comparisons
+	_ = a == b
+	_ = a != b
+	_ = a > b
+	_ = a >= b
+	_ = a < b
+	_ = a <= b
+	_ = a < b && c > d
+	_ = a < b || c > d
+
+	// spaces around "long" operands
+	_ = a + longIdentifier1
+	_ = longIdentifier1 + a
+	_ = longIdentifier1 + longIdentifier2*longIdentifier3
+	_ = s + "a longer string"
+
+	// some selected cases
+	_ = a + t0.x
+	_ = a + t0.x + t1.x*t2.x
+	_ = a + b + c + d + e + 2*3
+	_ = a + b + c + 2*3 + d + e
+	_ = (a + b + c) * 2
+	_ = a - b + c - d + (a + b + c) + d&e
+	_ = under_bar - 1
+	_ = Open(dpath+"/file", O_WRONLY|O_CREAT, 0666)
+	_ = int(c0&_Mask4)<<18 | int(c1&_Maskx)<<12 | int(c2&_Maskx)<<6 | int(c3&_Maskx)
+
+	// the parser does not restrict expressions that may appear as statements
+	true
+	42
+	"foo"
+	x
+	(x)
+	a + b
+	a + b + c
+	a + (b * c)
+	a + (b / c)
+	1 + a
+	a + 1
+	s[a]
+	x << 1
+	(s[0] << 1) & 0xf
+	"foo" + s
+	x == y
+	x < y || z > 42
+}
+
+func _() {
+	_ = a + b
+	_ = a + b + c
+	_ = a + b*c
+	_ = a + (b * c)
+	_ = (a + b) * c
+	_ = a + (b * c * d)
+	_ = a + (b*c + d)
+
+	_ = 1 << x
+	_ = -1 << x
+	_ = 1<<x - 1
+	_ = -1<<x - 1
+
+	_ = f(a + b)
+	_ = f(a + b + c)
+	_ = f(a + b*c)
+	_ = f(a + (b * c))
+	_ = f(1<<x-1, 1<<x-2)
+
+	_ = 1<<d.logWindowSize - 1
+
+	buf = make(x, 2*cap(b.buf)+n)
+
+	dst[i*3+2] = dbuf[0] << 2
+	dst[i*3+2] = dbuf[0]<<2 | dbuf[1]>>4
+
+	b.buf = b.buf[0 : b.off+m+n]
+	b.buf = b.buf[0 : b.off+m*n]
+	f(b.buf[0 : b.off+m+n])
+
+	signed += ' ' * 8
+	tw.octal(header[148:155], chksum)
+
+	_ = x > 0 && i >= 0
+
+	x1, x0 := x>>w2, x&m2
+	z0 = t1<<w2 + t0
+	z1 = (t1 + t0>>w2) >> w2
+	q1, r1 := x1/d1, x1%d1
+	r1 = r1*b2 | x0>>w2
+	x1 = (x1 << z) | (x0 >> (uint(w) - z))
+	x1 = x1<<z | x0>>(uint(w)-z)
+
+	_ = buf[0 : len(buf)+1]
+	_ = buf[0 : n+1]
+
+	a, b = b, a
+	a = b + c
+	a = b*c + d
+	_ = a*b + c
+	_ = a - b - c
+	_ = a - (b - c)
+	_ = a - b*c
+	_ = a - (b * c)
+	_ = a * b / c
+	_ = a / *b
+	_ = x[a|^b]
+	_ = x[a / *b]
+	_ = a & ^b
+	_ = a + +b
+	_ = a - -b
+	_ = x[a*-b]
+	_ = x[a + +b]
+	_ = x ^ y ^ z
+	_ = b[a>>24] ^ b[(a>>16)&0xFF] ^ b[(a>>8)&0xFF] ^ b[a&0xFF]
+	_ = len(longVariableName) * 2
+
+	_ = token(matchType + xlength<<lengthShift + xoffset)
+}
+
+func f(x int, args ...int) {
+	f(0, args...)
+	f(1, args)
+	f(2, args[0])
+
+	// make sure syntactically legal code remains syntactically legal
+	f(3, 42 ...)	// a blank must remain between 42 and ...
+	f(4, 42....)
+	f(5, 42....)
+	f(6, 42.0...)
+	f(7, 42.0...)
+	f(8, .42...)
+	f(9, .42...)
+	f(10, 42e0...)
+	f(11, 42e0...)
+
+	_ = 42 .x	// a blank must remain between 42 and .x
+	_ = 42..x
+	_ = 42..x
+	_ = 42.0.x
+	_ = 42.0.x
+	_ = .42.x
+	_ = .42.x
+	_ = 42e0.x
+	_ = 42e0.x
+
+	// a blank must remain between the binary operator and the 2nd operand
+	_ = x / *y
+	_ = x < -1
+	_ = x < <-1
+	_ = x + +1
+	_ = x - -1
+	_ = x & &x
+	_ = x & ^x
+
+	_ = f(x / *y, x < -1, x < <-1, x + +1, x - -1, x & &x, x & ^x)
+}
+
+func _() {
+	_ = T{}
+	_ = struct{}{}
+	_ = [10]T{}
+	_ = [...]T{}
+	_ = []T{}
+	_ = map[int]T{}
+}
+
+// one-line structs/interfaces in composite literals (up to a threshold)
+func _() {
+	_ = struct{}{}
+	_ = struct{ x int }{0}
+	_ = struct{ x, y, z int }{0, 1, 2}
+	_ = struct{ int }{0}
+	_ = struct{ s struct{ int } }{struct{ int }{0}}
+}
+
+func _() {
+	// do not modify literals
+	_ = "tab1	tab2	tab3	end"	// string contains 3 tabs
+	_ = "tab1 tab2 tab3 end"	// same string with 3 blanks - may be unaligned because editors see tabs in strings
+	_ = ""				// this comment should be aligned with the one on the previous line
+	_ = ``
+	_ = `
+`
+	_ = `foo
+		bar`
+	_ = `three spaces before the end of the line starting here:   
+they must not be removed`
+}
+
+func _() {
+	// smart handling of indentation for multi-line raw strings
+	var _ = ``
+	var _ = `foo`
+	var _ = `foo
+bar`
+
+	var _ = ``
+	var _ = `foo`
+	var _ =
+	// the next line should remain indented
+	`foo
+bar`
+
+	var _ =	// comment
+	``
+	var _ =	// comment
+	`foo`
+	var _ =	// comment
+	// the next line should remain indented
+	`foo
+bar`
+
+	var _ = /* comment */ ``
+	var _ = /* comment */ `foo`
+	var _ = /* comment */ `foo
+bar`
+
+	var _ =	/* comment */
+	``
+	var _ =	/* comment */
+	`foo`
+	var _ =	/* comment */
+	// the next line should remain indented
+	`foo
+bar`
+
+	var board = []int(
+		`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`)
+
+	var state = S{
+		"foo",
+		// the next line should remain indented
+		`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`,
+		"bar",
+	}
+}
+
+func _() {
+	// one-line function literals (body is on a single line)
+	_ = func() {}
+	_ = func() int { return 0 }
+	_ = func(x, y int) bool { m := (x + y) / 2; return m < 0 }
+
+	// multi-line function literals (body is not on one line)
+	_ = func() {
+	}
+	_ = func() int {
+		return 0
+	}
+	_ = func(x, y int) bool {
+		m := (x + y) / 2
+		return x < y
+	}
+
+	f(func() {
+	})
+	f(func() int {
+		return 0
+	})
+	f(func(x, y int) bool {
+		m := (x + y) / 2
+		return x < y
+	})
+}
+
+func _() {
+	_ = [][]int{
+		[]int{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int{
+		{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int{
+		{1},
+		{1, 2},
+		{1, 2, 3},
+	}
+	_ = [][]int{{1}, {1, 2}, {1, 2, 3}}
+}
+
+// various multi-line expressions
+func _() {
+	// do not add extra indentation to multi-line string lists
+	_ = "foo" + "bar"
+	_ = "foo" +
+		"bar" +
+		"bah"
+	_ = []string{
+		"abc" +
+			"def",
+		"foo" +
+			"bar",
+	}
+}
+
+const _ = F1 +
+	`string = "%s";` +
+	`ptr = *;` +
+	`datafmt.T2 = s ["-" p "-"];`
+
+const _ = `datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+
+const _ = `datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+
+func _() {
+	_ = F1 +
+		`string = "%s";` +
+		`ptr = *;` +
+		`datafmt.T2 = s ["-" p "-"];`
+
+	_ =
+		`datafmt "datafmt";` +
+			`default = "%v";` +
+			`array = *;` +
+			`datafmt.T3 = s  {" " a a / ","};`
+
+	_ = `datafmt "datafmt";` +
+		`default = "%v";` +
+		`array = *;` +
+		`datafmt.T3 = s  {" " a a / ","};`
+}
+
+func _() {
+	// respect source lines in multi-line expressions
+	_ = a +
+		b +
+		c
+	_ = a < b ||
+		b < a
+	_ = "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000"	// 100!
+	_ = "170141183460469231731687303715884105727"	// prime
+}
+
+// Alignment after overlong lines
+const (
+	_	= "991"
+	_	= "2432902008176640000"	// 20!
+	_	= "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000"	// 100!
+	_	= "170141183460469231731687303715884105727"	// prime
+)
+
+// Correct placement of operators and comments in multi-line expressions
+func _() {
+	_ = a +	// comment
+		b +	// comment
+		c
+	_ = "a" +
+		"b" +	// comment
+		"c"
+	_ = "ba0408" + "7265717569726564"	// field 71, encoding 2, string "required"
+}
+
+// Correct placement of terminating comma/closing parentheses in multi-line calls.
+func _() {
+	f(1,
+		2,
+		3)
+	f(1,
+		2,
+		3,
+	)
+	f(1,
+		2,
+		3)	// comment
+	f(1,
+		2,
+		3,	// comment
+	)
+	f(1,
+		2,
+		3)	// comment
+	f(1,
+		2,
+		3,	// comment
+	)
+}
+
+// Align comments in multi-line lists of single-line expressions.
+var txpix = [NCOL]draw.Color{
+	draw.Yellow,		// yellow
+	draw.Cyan,		// cyan
+	draw.Green,		// lime green
+	draw.GreyBlue,		// slate
+	draw.Red,		/* red */
+	draw.GreyGreen,		/* olive green */
+	draw.Blue,		/* blue */
+	draw.Color(0xFF55AAFF),	/* pink */
+	draw.Color(0xFFAAFFFF),	/* lavender */
+	draw.Color(0xBB005DFF),	/* maroon */
+}
+
+func same(t, u *Time) bool {
+	// respect source lines in multi-line expressions
+	return t.Year == u.Year &&
+		t.Month == u.Month &&
+		t.Day == u.Day &&
+		t.Hour == u.Hour &&
+		t.Minute == u.Minute &&
+		t.Second == u.Second &&
+		t.Weekday == u.Weekday &&
+		t.ZoneOffset == u.ZoneOffset &&
+		t.Zone == u.Zone
+}
+
+func (p *parser) charClass() {
+	// respect source lines in multi-line expressions
+	if cc.negate && len(cc.ranges) == 2 &&
+		cc.ranges[0] == '\n' && cc.ranges[1] == '\n' {
+		nl := new(_NotNl)
+		p.re.add(nl)
+	}
+}
+
+func addState(s []state, inst instr, match []int) {
+	// handle comments correctly in multi-line expressions
+	for i := 0; i < l; i++ {
+		if s[i].inst.index() == index &&	// same instruction
+			s[i].match[0] < pos {	// earlier match already going; leftmost wins
+			return s
+		}
+	}
+}
+
+func (self *T) foo(x int) *T	{ return self }
+
+func _()	{ module.Func1().Func2() }
+
+func _() {
+	_ = new(T).
+		foo(1).
+		foo(2).
+		foo(3)
+
+	_ = new(T).
+		foo(1).
+		foo(2).	// inline comments
+		foo(3)
+
+	_ = new(T).foo(1).foo(2).foo(3)
+
+	// handle multiline argument list correctly
+	_ = new(T).
+		foo(
+			1).
+		foo(2)
+
+	_ = new(T).foo(
+		1).foo(2)
+
+	_ = Array[3+
+		4]
+
+	_ = Method(1, 2,
+		3)
+
+	_ = new(T).
+		foo().
+		bar().(*Type)
+
+	_ = new(T).
+		foo().
+		bar().(*Type).
+		baz()
+
+	_ = new(T).
+		foo().
+		bar()["idx"]
+
+	_ = new(T).
+		foo().
+		bar()["idx"].
+		baz()
+
+	_ = new(T).
+		foo().
+		bar()[1:2]
+
+	_ = new(T).
+		foo().
+		bar()[1:2].
+		baz()
+
+	_ = new(T).
+		Field.
+		Array[3+
+			4].
+		Table["foo"].
+		Blob.(*Type).
+		Slices[1:4].
+		Method(1, 2,
+			3).
+		Thingy
+
+	_ = a.b.c
+	_ = a.
+		b.
+		c
+	_ = a.b().c
+	_ = a.
+		b().
+		c
+	_ = a.b[0].c
+	_ = a.
+		b[0].
+		c
+	_ = a.b[0:].c
+	_ = a.
+		b[0:].
+		c
+	_ = a.b.(T).c
+	_ = a.
+		b.(T).
+		c
+}
+
+// Don't introduce extra newlines in strangely formatted expression lists.
+func f() {
+	// os.Open parameters should remain on two lines
+	if writer, err = os.Open(outfile, s.O_WRONLY|os.O_CREATE|
+		os.O_TRUNC, 0666); err != nil {
+		log.Fatal(err)
+	}
+}
diff --git a/src/pkg/go/printer/testdata/expressions.input b/src/pkg/go/printer/testdata/expressions.input
new file mode 100644
index 000000000..d11314983
--- /dev/null
+++ b/src/pkg/go/printer/testdata/expressions.input
@@ -0,0 +1,656 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package expressions
+
+type T struct {
+	x, y, z int
+}
+
+var (
+	a, b, c, d, e int
+	under_bar int
+	longIdentifier1, longIdentifier2, longIdentifier3 int
+	t0, t1, t2 T
+	s string
+	p *int
+)
+
+
+func _() {
+	// no spaces around simple or parenthesized expressions
+	_ = (a+0)
+	_ = a+b
+	_ = a+b+c
+	_ = a+b-c
+	_ = a-b-c
+	_ = a+(b*c)
+	_ = a+(b/c)
+	_ = a-(b%c)
+	_ = 1+a
+	_ = a+1
+	_ = a+b+1
+	_ = s[a]
+	_ = s[a:]
+	_ = s[:b]
+	_ = s[1:2]
+	_ = s[a:b]
+	_ = s[0:len(s)]
+	_ = s[0]<<1
+	_ = (s[0]<<1)&0xf
+	_ = s[0] << 2 | s[1] >> 4
+	_ = "foo"+s
+	_ = s+"foo"
+	_ = 'a'+'b'
+	_ = len(s)/2
+	_ = len(t0.x)/a
+
+	// spaces around expressions of different precedence or expressions containing spaces
+	_ = a + -b
+	_ = a - ^b
+	_ = a / *p
+	_ = a + b*c
+	_ = 1 + b*c
+	_ = a + 2*c
+	_ = a + c*2
+	_ = 1 + 2*3
+	_ = s[1 : 2*3]
+	_ = s[a : b-c]
+	_ = s[0:]
+	_ = s[a+b]
+	_ = s[: b-c]
+	_ = s[a+b :]
+	_ = a[a<<b+1]
+	_ = a[a<<b+1 :]
+	_ = s[a+b : len(s)]
+	_ = s[len(s) : -a]
+	_ = s[a : len(s)+1]
+	_ = s[a : len(s)+1]+s
+
+	// spaces around operators with equal or lower precedence than comparisons
+	_ = a == b
+	_ = a != b
+	_ = a > b
+	_ = a >= b
+	_ = a < b
+	_ = a <= b
+	_ = a < b && c > d
+	_ = a < b || c > d
+
+	// spaces around "long" operands
+	_ = a + longIdentifier1
+	_ = longIdentifier1 + a
+	_ = longIdentifier1 + longIdentifier2 * longIdentifier3
+	_ = s + "a longer string"
+
+	// some selected cases
+	_ = a + t0.x
+	_ = a + t0.x + t1.x * t2.x
+	_ = a + b + c + d + e + 2*3
+	_ = a + b + c + 2*3 + d + e
+	_ = (a+b+c)*2
+	_ = a - b + c - d + (a+b+c) + d&e
+	_ = under_bar-1
+	_ = Open(dpath + "/file", O_WRONLY | O_CREAT, 0666)
+	_ = int(c0&_Mask4)<<18 | int(c1&_Maskx)<<12 | int(c2&_Maskx)<<6 | int(c3&_Maskx)
+
+	// the parser does not restrict expressions that may appear as statements
+	true
+	42
+	"foo"
+	x
+	(x)
+	a+b
+	a+b+c
+	a+(b*c)
+	a+(b/c)
+	1+a
+	a+1
+	s[a]
+	x<<1
+	(s[0]<<1)&0xf
+	"foo"+s
+	x == y
+	x < y || z > 42
+}
+
+
+func _() {
+	_ = a+b
+	_ = a+b+c
+	_ = a+b*c
+	_ = a+(b*c)
+	_ = (a+b)*c
+	_ = a+(b*c*d)
+	_ = a+(b*c+d)
+
+	_ = 1<<x
+	_ = -1<<x
+	_ = 1<<x-1
+	_ = -1<<x-1
+
+	_ = f(a+b)
+	_ = f(a+b+c)
+	_ = f(a+b*c)
+	_ = f(a+(b*c))
+	_ = f(1<<x-1, 1<<x-2)
+
+	_ = 1<<d.logWindowSize-1
+
+	buf = make(x, 2*cap(b.buf) + n)
+
+	dst[i*3+2] = dbuf[0]<<2
+	dst[i*3+2] = dbuf[0]<<2 | dbuf[1]>>4
+
+	b.buf = b.buf[0:b.off+m+n]
+	b.buf = b.buf[0:b.off+m*n]
+	f(b.buf[0:b.off+m+n])
+
+	signed += ' '*8
+	tw.octal(header[148:155], chksum)
+
+	_ = x > 0 && i >= 0
+
+	x1, x0 := x>>w2, x&m2
+	z0 = t1<<w2+t0
+	z1 = (t1+t0>>w2)>>w2
+	q1, r1 := x1/d1, x1%d1
+	r1 = r1*b2 | x0>>w2
+	x1 = (x1<<z)|(x0>>(uint(w)-z))
+	x1 = x1<<z | x0>>(uint(w)-z)
+
+	_ = buf[0:len(buf)+1]
+	_ = buf[0:n+1]
+
+	a,b = b,a
+	a = b+c
+	a = b*c+d
+	_ = a*b+c
+	_ = a-b-c
+	_ = a-(b-c)
+	_ = a-b*c
+	_ = a-(b*c)
+	_ = a*b/c
+	_ = a/ *b
+	_ = x[a|^b]
+	_ = x[a/ *b]
+	_ = a& ^b
+	_ = a+ +b
+	_ = a- -b
+	_ = x[a*-b]
+	_ = x[a+ +b]
+	_ = x^y^z
+	_ = b[a>>24] ^ b[(a>>16)&0xFF] ^ b[(a>>8)&0xFF] ^ b[a&0xFF]
+	_ = len(longVariableName)*2
+
+	_ = token(matchType + xlength<<lengthShift + xoffset)
+}
+
+
+func f(x int, args ...int) {
+	f(0, args...)
+	f(1, args)
+	f(2, args[0])
+
+	// make sure syntactically legal code remains syntactically legal
+	f(3, 42 ...) // a blank must remain between 42 and ...
+	f(4, 42. ...)
+	f(5, 42....)
+	f(6, 42.0 ...)
+	f(7, 42.0...)
+	f(8, .42 ...)
+	f(9, .42...)
+	f(10, 42e0 ...)
+	f(11, 42e0...)
+
+	_ = 42 .x // a blank must remain between 42 and .x
+	_ = 42. .x
+	_ = 42..x
+	_ = 42.0 .x
+	_ = 42.0.x
+	_ = .42 .x
+	_ = .42.x
+	_ = 42e0 .x
+	_ = 42e0.x
+
+	// a blank must remain between the binary operator and the 2nd operand
+	_ = x/ *y
+	_ = x< -1
+	_ = x< <-1
+	_ = x+ +1
+	_ = x- -1
+	_ = x& &x
+	_ = x& ^x
+
+	_ = f(x/ *y, x< -1, x< <-1, x+ +1, x- -1, x& &x, x& ^x)
+}
+
+
+func _() {
+	_ = T{}
+	_ = struct{}{}
+	_ = [10]T{}
+	_ = [...]T{}
+	_ = []T{}
+	_ = map[int]T{}
+}
+
+
+// one-line structs/interfaces in composite literals (up to a threshold)
+func _() {
+	_ = struct{}{}
+	_ = struct{ x int }{0}
+	_ = struct{ x, y, z int }{0, 1, 2}
+	_ = struct{ int }{0}
+	_ = struct{ s struct { int } }{struct{ int}{0} }
+}
+
+
+func _() {
+	// do not modify literals
+	_ = "tab1	tab2	tab3	end"  // string contains 3 tabs
+	_ = "tab1 tab2 tab3 end"  // same string with 3 blanks - may be unaligned because editors see tabs in strings
+	_ = ""  // this comment should be aligned with the one on the previous line
+	_ = ``
+	_ = `
+`
+_ = `foo
+		bar`
+	_ = `three spaces before the end of the line starting here:   
+they must not be removed`
+}
+
+
+func _() {
+	// smart handling of indentation for multi-line raw strings
+	var _ = ``
+	var _ = `foo`
+	var _ = `foo
+bar`
+
+
+var _ =
+	``
+var _ =
+	`foo`
+var _ =
+	// the next line should remain indented
+	`foo
+bar`
+
+
+	var _ = // comment
+		``
+	var _ = // comment
+		`foo`
+	var _ = // comment
+		// the next line should remain indented
+		`foo
+bar`
+
+
+var _ = /* comment */ ``
+var _ = /* comment */ `foo`
+var _ = /* comment */ `foo
+bar`
+
+
+	var _ = /* comment */
+		``
+	var _ = /* comment */
+		`foo`
+	var _ = /* comment */
+		// the next line should remain indented
+		`foo
+bar`
+
+
+var board = []int(
+	`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`)
+
+
+	var state = S{
+		"foo",
+		// the next line should remain indented
+		`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`,
+		"bar",
+	}
+}
+
+
+func _() {
+	// one-line function literals (body is on a single line)
+	_ = func() {}
+	_ = func() int { return 0 }
+	_ = func(x, y int) bool { m := (x+y)/2; return m < 0 }
+
+	// multi-line function literals (body is not on one line)
+	_ = func() {
+	}
+	_ = func() int {
+		return 0
+	}
+	_ = func(x, y int) bool {
+		m := (x+y)/2; return x < y }
+
+	f(func() {
+	})
+	f(func() int {
+		return 0
+	})
+	f(func(x, y int) bool {
+		m := (x+y)/2; return x < y })
+}
+
+
+func _() {
+	_ = [][]int {
+		[]int{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int {
+		{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int {
+		{1},
+		{1, 2},
+		{1, 2, 3},
+	}
+	_ = [][]int {{1}, {1, 2}, {1, 2, 3}}
+}
+
+
+// various multi-line expressions
+func _() {
+	// do not add extra indentation to multi-line string lists
+	_ = "foo" + "bar"
+	_ = "foo" +
+	"bar" +
+	"bah"
+	_ = []string {
+		"abc" +
+		"def",
+		"foo" +
+		"bar",
+	}
+}
+
+
+const _ = F1 +
+	`string = "%s";` +
+	`ptr = *;` +
+	`datafmt.T2 = s ["-" p "-"];`
+
+
+const _ =
+	`datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+
+
+const _ = `datafmt "datafmt";` +
+`default = "%v";` +
+`array = *;` +
+`datafmt.T3 = s  {" " a a / ","};`
+
+
+func _() {
+	_ = F1 +
+		`string = "%s";` +
+		`ptr = *;` +
+		`datafmt.T2 = s ["-" p "-"];`
+
+	_ =
+		`datafmt "datafmt";` +
+		`default = "%v";` +
+		`array = *;` +
+		`datafmt.T3 = s  {" " a a / ","};`
+
+	_ = `datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+}
+
+
+func _() {
+	// respect source lines in multi-line expressions
+	_ = a+
+	b+
+	c
+	_ = a < b ||
+		b < a
+	_ = "933262154439441526816992388562667004907159682643816214685929" +
+	"638952175999932299156089414639761565182862536979208272237582" +
+	"51185210916864000000000000000000000000"  // 100!
+	_ = "170141183460469231731687303715884105727"  // prime
+}
+
+
+// Alignment after overlong lines
+const (
+	_ = "991"
+	_ = "2432902008176640000"  // 20!
+	_ = "933262154439441526816992388562667004907159682643816214685929" +
+	"638952175999932299156089414639761565182862536979208272237582" +
+	"51185210916864000000000000000000000000"  // 100!
+	_ = "170141183460469231731687303715884105727"  // prime
+)
+
+
+// Correct placement of operators and comments in multi-line expressions
+func _() {
+	_ = a +  // comment
+		b +  // comment
+		c
+	_ = "a"	+
+		"b" +	// comment
+		"c"
+	_ = "ba0408" + "7265717569726564"     // field 71, encoding 2, string "required"
+}
+
+
+// Correct placement of terminating comma/closing parentheses in multi-line calls.
+func _() {
+	f(1,
+		2,
+		3)
+	f(1,
+		2,
+		3,
+	)
+	f(1,
+		2,
+		3)  // comment
+	f(1,
+		2,
+		3,  // comment
+	)
+	f(1,
+		2,
+		3)// comment
+	f(1,
+		2,
+		3,// comment
+	)
+}
+
+
+// Align comments in multi-line lists of single-line expressions.
+var txpix = [NCOL]draw.Color{
+	draw.Yellow, // yellow
+	draw.Cyan, // cyan
+	draw.Green, // lime green
+	draw.GreyBlue, // slate
+	draw.Red, /* red */
+	draw.GreyGreen, /* olive green */
+	draw.Blue, /* blue */
+	draw.Color(0xFF55AAFF), /* pink */
+	draw.Color(0xFFAAFFFF), /* lavender */
+	draw.Color(0xBB005DFF), /* maroon */
+}
+
+
+func same(t, u *Time) bool {
+	// respect source lines in multi-line expressions
+	return t.Year == u.Year &&
+		t.Month == u.Month &&
+		t.Day == u.Day &&
+		t.Hour == u.Hour &&
+		t.Minute == u.Minute &&
+		t.Second == u.Second &&
+		t.Weekday == u.Weekday &&
+		t.ZoneOffset == u.ZoneOffset &&
+		t.Zone == u.Zone
+}
+
+
+func (p *parser) charClass() {
+	// respect source lines in multi-line expressions
+	if cc.negate && len(cc.ranges) == 2 &&
+		cc.ranges[0] == '\n' && cc.ranges[1] == '\n' {
+		nl := new(_NotNl)
+		p.re.add(nl)
+	}
+}
+
+
+func addState(s []state, inst instr, match []int) {
+	// handle comments correctly in multi-line expressions
+	for i := 0; i < l; i++ {
+		if s[i].inst.index() == index && // same instruction
+		   s[i].match[0] < pos {	// earlier match already going; leftmost wins
+		   	return s
+		 }
+	}
+}
+
+func (self *T) foo(x int) *T { return self }
+
+func _() { module.Func1().Func2() }
+
+func _() {
+	_ = new(T).
+		foo(1).
+			foo(2).
+		foo(3)
+
+	_ = new(T).
+	foo(1).
+	foo(2). // inline comments
+	foo(3)
+
+	_ = new(T).foo(1).foo(2).foo(3)
+
+	// handle multiline argument list correctly
+	_ = new(T).
+	foo(
+		1).
+		foo(2)
+
+	_ = new(T).foo(
+		1).foo(2)
+
+	_ = Array[3 +
+4]
+
+	_ = Method(1, 2,
+		3)
+
+	_ = new(T).
+   foo().
+   bar() . (*Type)
+
+	_ = new(T).
+foo().
+bar().(*Type).
+baz()
+
+	_ = new(T).
+	foo().
+	bar()["idx"]
+
+	_ = new(T).
+	foo().
+	bar()["idx"]	.
+	baz()
+
+	_ = new(T).
+	foo().
+	bar()[1:2]
+
+	_ = new(T).
+	foo().
+	bar()[1:2].
+	baz()
+
+	_ = new(T).
+		Field.
+		Array[3+
+       		4].
+		Table ["foo"].
+		Blob. (*Type).
+	Slices[1:4].
+	Method(1, 2,
+	3).
+		Thingy
+
+	_ = a.b.c
+	_ = a.
+	b.
+	c
+	_ = a.b().c
+	_ = a.
+	b().
+	c
+	_ = a.b[0].c
+	_ = a.
+	b[0].
+	c
+	_ = a.b[0:].c
+	_ = a.
+	b[0:].
+	c
+	_ = a.b.(T).c
+	_ = a.
+	b.
+	(T).
+	c
+}
+
+
+// Don't introduce extra newlines in strangely formatted expression lists.
+func f() {
+	// os.Open parameters should remain on two lines
+	if writer, err = os.Open(outfile, s.O_WRONLY|os.O_CREATE|
+		os.O_TRUNC, 0666); err != nil {
+	    log.Fatal(err)
+	}
+}
diff --git a/src/pkg/go/printer/testdata/expressions.raw b/src/pkg/go/printer/testdata/expressions.raw
new file mode 100644
index 000000000..d7819a3ba
--- /dev/null
+++ b/src/pkg/go/printer/testdata/expressions.raw
@@ -0,0 +1,627 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package expressions
+
+type T struct {
+	x, y, z int
+}
+
+var (
+	a, b, c, d, e	int
+	under_bar	int
+	longIdentifier1, longIdentifier2, longIdentifier3	int
+	t0, t1, t2	T
+	s	string
+	p	*int
+)
+
+func _() {
+	// no spaces around simple or parenthesized expressions
+	_ = (a + 0)
+	_ = a + b
+	_ = a + b + c
+	_ = a + b - c
+	_ = a - b - c
+	_ = a + (b * c)
+	_ = a + (b / c)
+	_ = a - (b % c)
+	_ = 1 + a
+	_ = a + 1
+	_ = a + b + 1
+	_ = s[a]
+	_ = s[a:]
+	_ = s[:b]
+	_ = s[1:2]
+	_ = s[a:b]
+	_ = s[0:len(s)]
+	_ = s[0] << 1
+	_ = (s[0] << 1) & 0xf
+	_ = s[0]<<2 | s[1]>>4
+	_ = "foo" + s
+	_ = s + "foo"
+	_ = 'a' + 'b'
+	_ = len(s) / 2
+	_ = len(t0.x) / a
+
+	// spaces around expressions of different precedence or expressions containing spaces
+	_ = a + -b
+	_ = a - ^b
+	_ = a / *p
+	_ = a + b*c
+	_ = 1 + b*c
+	_ = a + 2*c
+	_ = a + c*2
+	_ = 1 + 2*3
+	_ = s[1 : 2*3]
+	_ = s[a : b-c]
+	_ = s[0:]
+	_ = s[a+b]
+	_ = s[:b-c]
+	_ = s[a+b:]
+	_ = a[a<<b+1]
+	_ = a[a<<b+1:]
+	_ = s[a+b : len(s)]
+	_ = s[len(s):-a]
+	_ = s[a : len(s)+1]
+	_ = s[a:len(s)+1] + s
+
+	// spaces around operators with equal or lower precedence than comparisons
+	_ = a == b
+	_ = a != b
+	_ = a > b
+	_ = a >= b
+	_ = a < b
+	_ = a <= b
+	_ = a < b && c > d
+	_ = a < b || c > d
+
+	// spaces around "long" operands
+	_ = a + longIdentifier1
+	_ = longIdentifier1 + a
+	_ = longIdentifier1 + longIdentifier2*longIdentifier3
+	_ = s + "a longer string"
+
+	// some selected cases
+	_ = a + t0.x
+	_ = a + t0.x + t1.x*t2.x
+	_ = a + b + c + d + e + 2*3
+	_ = a + b + c + 2*3 + d + e
+	_ = (a + b + c) * 2
+	_ = a - b + c - d + (a + b + c) + d&e
+	_ = under_bar - 1
+	_ = Open(dpath+"/file", O_WRONLY|O_CREAT, 0666)
+	_ = int(c0&_Mask4)<<18 | int(c1&_Maskx)<<12 | int(c2&_Maskx)<<6 | int(c3&_Maskx)
+
+	// the parser does not restrict expressions that may appear as statements
+	true
+	42
+	"foo"
+	x
+	(x)
+	a + b
+	a + b + c
+	a + (b * c)
+	a + (b / c)
+	1 + a
+	a + 1
+	s[a]
+	x << 1
+	(s[0] << 1) & 0xf
+	"foo" + s
+	x == y
+	x < y || z > 42
+}
+
+func _() {
+	_ = a + b
+	_ = a + b + c
+	_ = a + b*c
+	_ = a + (b * c)
+	_ = (a + b) * c
+	_ = a + (b * c * d)
+	_ = a + (b*c + d)
+
+	_ = 1 << x
+	_ = -1 << x
+	_ = 1<<x - 1
+	_ = -1<<x - 1
+
+	_ = f(a + b)
+	_ = f(a + b + c)
+	_ = f(a + b*c)
+	_ = f(a + (b * c))
+	_ = f(1<<x-1, 1<<x-2)
+
+	_ = 1<<d.logWindowSize - 1
+
+	buf = make(x, 2*cap(b.buf)+n)
+
+	dst[i*3+2] = dbuf[0] << 2
+	dst[i*3+2] = dbuf[0]<<2 | dbuf[1]>>4
+
+	b.buf = b.buf[0 : b.off+m+n]
+	b.buf = b.buf[0 : b.off+m*n]
+	f(b.buf[0 : b.off+m+n])
+
+	signed += ' ' * 8
+	tw.octal(header[148:155], chksum)
+
+	_ = x > 0 && i >= 0
+
+	x1, x0 := x>>w2, x&m2
+	z0 = t1<<w2 + t0
+	z1 = (t1 + t0>>w2) >> w2
+	q1, r1 := x1/d1, x1%d1
+	r1 = r1*b2 | x0>>w2
+	x1 = (x1 << z) | (x0 >> (uint(w) - z))
+	x1 = x1<<z | x0>>(uint(w)-z)
+
+	_ = buf[0 : len(buf)+1]
+	_ = buf[0 : n+1]
+
+	a, b = b, a
+	a = b + c
+	a = b*c + d
+	_ = a*b + c
+	_ = a - b - c
+	_ = a - (b - c)
+	_ = a - b*c
+	_ = a - (b * c)
+	_ = a * b / c
+	_ = a / *b
+	_ = x[a|^b]
+	_ = x[a / *b]
+	_ = a & ^b
+	_ = a + +b
+	_ = a - -b
+	_ = x[a*-b]
+	_ = x[a + +b]
+	_ = x ^ y ^ z
+	_ = b[a>>24] ^ b[(a>>16)&0xFF] ^ b[(a>>8)&0xFF] ^ b[a&0xFF]
+	_ = len(longVariableName) * 2
+
+	_ = token(matchType + xlength<<lengthShift + xoffset)
+}
+
+func f(x int, args ...int) {
+	f(0, args...)
+	f(1, args)
+	f(2, args[0])
+
+	// make sure syntactically legal code remains syntactically legal
+	f(3, 42 ...)	// a blank must remain between 42 and ...
+	f(4, 42....)
+	f(5, 42....)
+	f(6, 42.0...)
+	f(7, 42.0...)
+	f(8, .42...)
+	f(9, .42...)
+	f(10, 42e0...)
+	f(11, 42e0...)
+
+	_ = 42 .x	// a blank must remain between 42 and .x
+	_ = 42..x
+	_ = 42..x
+	_ = 42.0.x
+	_ = 42.0.x
+	_ = .42.x
+	_ = .42.x
+	_ = 42e0.x
+	_ = 42e0.x
+
+	// a blank must remain between the binary operator and the 2nd operand
+	_ = x / *y
+	_ = x < -1
+	_ = x < <-1
+	_ = x + +1
+	_ = x - -1
+	_ = x & &x
+	_ = x & ^x
+
+	_ = f(x / *y, x < -1, x < <-1, x + +1, x - -1, x & &x, x & ^x)
+}
+
+func _() {
+	_ = T{}
+	_ = struct{}{}
+	_ = [10]T{}
+	_ = [...]T{}
+	_ = []T{}
+	_ = map[int]T{}
+}
+
+// one-line structs/interfaces in composite literals (up to a threshold)
+func _() {
+	_ = struct{}{}
+	_ = struct{ x int }{0}
+	_ = struct{ x, y, z int }{0, 1, 2}
+	_ = struct{ int }{0}
+	_ = struct{ s struct{ int } }{struct{ int }{0}}
+}
+
+func _() {
+	// do not modify literals
+	_ = "tab1	tab2	tab3	end"	// string contains 3 tabs
+	_ = "tab1 tab2 tab3 end"	// same string with 3 blanks - may be unaligned because editors see tabs in strings
+	_ = ""	// this comment should be aligned with the one on the previous line
+	_ = ``
+	_ = `
+`
+	_ = `foo
+		bar`
+	_ = `three spaces before the end of the line starting here:   
+they must not be removed`
+}
+
+func _() {
+	// smart handling of indentation for multi-line raw strings
+	var _ = ``
+	var _ = `foo`
+	var _ = `foo
+bar`
+
+	var _ = ``
+	var _ = `foo`
+	var _ =
+	// the next line should remain indented
+	`foo
+bar`
+
+	var _ =	// comment
+	``
+	var _ =	// comment
+	`foo`
+	var _ =	// comment
+	// the next line should remain indented
+	`foo
+bar`
+
+	var _ = /* comment */ ``
+	var _ = /* comment */ `foo`
+	var _ = /* comment */ `foo
+bar`
+
+	var _ =	/* comment */
+	``
+	var _ =	/* comment */
+	`foo`
+	var _ =	/* comment */
+	// the next line should remain indented
+	`foo
+bar`
+
+	var board = []int(
+		`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`)
+
+	var state = S{
+		"foo",
+		// the next line should remain indented
+		`...........
+...........
+....●●●....
+....●●●....
+..●●●●●●●..
+..●●●○●●●..
+..●●●●●●●..
+....●●●....
+....●●●....
+...........
+...........
+`,
+		"bar",
+	}
+}
+
+func _() {
+	// one-line function literals (body is on a single line)
+	_ = func() {}
+	_ = func() int { return 0 }
+	_ = func(x, y int) bool { m := (x + y) / 2; return m < 0 }
+
+	// multi-line function literals (body is not on one line)
+	_ = func() {
+	}
+	_ = func() int {
+		return 0
+	}
+	_ = func(x, y int) bool {
+		m := (x + y) / 2
+		return x < y
+	}
+
+	f(func() {
+	})
+	f(func() int {
+		return 0
+	})
+	f(func(x, y int) bool {
+		m := (x + y) / 2
+		return x < y
+	})
+}
+
+func _() {
+	_ = [][]int{
+		[]int{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int{
+		{1},
+		[]int{1, 2},
+		[]int{1, 2, 3},
+	}
+	_ = [][]int{
+		{1},
+		{1, 2},
+		{1, 2, 3},
+	}
+	_ = [][]int{{1}, {1, 2}, {1, 2, 3}}
+}
+
+// various multi-line expressions
+func _() {
+	// do not add extra indentation to multi-line string lists
+	_ = "foo" + "bar"
+	_ = "foo" +
+		"bar" +
+		"bah"
+	_ = []string{
+		"abc" +
+			"def",
+		"foo" +
+			"bar",
+	}
+}
+
+const _ = F1 +
+	`string = "%s";` +
+	`ptr = *;` +
+	`datafmt.T2 = s ["-" p "-"];`
+
+const _ = `datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+
+const _ = `datafmt "datafmt";` +
+	`default = "%v";` +
+	`array = *;` +
+	`datafmt.T3 = s  {" " a a / ","};`
+
+func _() {
+	_ = F1 +
+		`string = "%s";` +
+		`ptr = *;` +
+		`datafmt.T2 = s ["-" p "-"];`
+
+	_ =
+		`datafmt "datafmt";` +
+			`default = "%v";` +
+			`array = *;` +
+			`datafmt.T3 = s  {" " a a / ","};`
+
+	_ = `datafmt "datafmt";` +
+		`default = "%v";` +
+		`array = *;` +
+		`datafmt.T3 = s  {" " a a / ","};`
+}
+
+func _() {
+	// respect source lines in multi-line expressions
+	_ = a +
+		b +
+		c
+	_ = a < b ||
+		b < a
+	_ = "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000"	// 100!
+	_ = "170141183460469231731687303715884105727"	// prime
+}
+
+// Alignment after overlong lines
+const (
+	_	= "991"
+	_	= "2432902008176640000"		// 20!
+	_	= "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000"	// 100!
+	_	= "170141183460469231731687303715884105727"		// prime
+)
+
+// Correct placement of operators and comments in multi-line expressions
+func _() {
+	_ = a +	// comment
+		b +	// comment
+		c
+	_ = "a" +
+		"b" +	// comment
+		"c"
+	_ = "ba0408" + "7265717569726564"	// field 71, encoding 2, string "required"
+}
+
+// Correct placement of terminating comma/closing parentheses in multi-line calls.
+func _() {
+	f(1,
+		2,
+		3)
+	f(1,
+		2,
+		3,
+	)
+	f(1,
+		2,
+		3)	// comment
+	f(1,
+		2,
+		3,	// comment
+	)
+	f(1,
+		2,
+		3)	// comment
+	f(1,
+		2,
+		3,	// comment
+	)
+}
+
+// Align comments in multi-line lists of single-line expressions.
+var txpix = [NCOL]draw.Color{
+	draw.Yellow,	// yellow
+	draw.Cyan,	// cyan
+	draw.Green,	// lime green
+	draw.GreyBlue,	// slate
+	draw.Red,	/* red */
+	draw.GreyGreen,	/* olive green */
+	draw.Blue,	/* blue */
+	draw.Color(0xFF55AAFF),	/* pink */
+	draw.Color(0xFFAAFFFF),	/* lavender */
+	draw.Color(0xBB005DFF),	/* maroon */
+}
+
+func same(t, u *Time) bool {
+	// respect source lines in multi-line expressions
+	return t.Year == u.Year &&
+		t.Month == u.Month &&
+		t.Day == u.Day &&
+		t.Hour == u.Hour &&
+		t.Minute == u.Minute &&
+		t.Second == u.Second &&
+		t.Weekday == u.Weekday &&
+		t.ZoneOffset == u.ZoneOffset &&
+		t.Zone == u.Zone
+}
+
+func (p *parser) charClass() {
+	// respect source lines in multi-line expressions
+	if cc.negate && len(cc.ranges) == 2 &&
+		cc.ranges[0] == '\n' && cc.ranges[1] == '\n' {
+		nl := new(_NotNl)
+		p.re.add(nl)
+	}
+}
+
+func addState(s []state, inst instr, match []int) {
+	// handle comments correctly in multi-line expressions
+	for i := 0; i < l; i++ {
+		if s[i].inst.index() == index &&	// same instruction
+			s[i].match[0] < pos {	// earlier match already going; leftmost wins
+			return s
+		}
+	}
+}
+
+func (self *T) foo(x int) *T	{ return self }
+
+func _()	{ module.Func1().Func2() }
+
+func _() {
+	_ = new(T).
+		foo(1).
+		foo(2).
+		foo(3)
+
+	_ = new(T).
+		foo(1).
+		foo(2).	// inline comments
+		foo(3)
+
+	_ = new(T).foo(1).foo(2).foo(3)
+
+	// handle multiline argument list correctly
+	_ = new(T).
+		foo(
+			1).
+		foo(2)
+
+	_ = new(T).foo(
+		1).foo(2)
+
+	_ = Array[3+
+		4]
+
+	_ = Method(1, 2,
+		3)
+
+	_ = new(T).
+		foo().
+		bar().(*Type)
+
+	_ = new(T).
+		foo().
+		bar().(*Type).
+		baz()
+
+	_ = new(T).
+		foo().
+		bar()["idx"]
+
+	_ = new(T).
+		foo().
+		bar()["idx"].
+		baz()
+
+	_ = new(T).
+		foo().
+		bar()[1:2]
+
+	_ = new(T).
+		foo().
+		bar()[1:2].
+		baz()
+
+	_ = new(T).
+		Field.
+		Array[3+
+			4].
+		Table["foo"].
+		Blob.(*Type).
+		Slices[1:4].
+		Method(1, 2,
+			3).
+		Thingy
+
+	_ = a.b.c
+	_ = a.
+		b.
+		c
+	_ = a.b().c
+	_ = a.
+		b().
+		c
+	_ = a.b[0].c
+	_ = a.
+		b[0].
+		c
+	_ = a.b[0:].c
+	_ = a.
+		b[0:].
+		c
+	_ = a.b.(T).c
+	_ = a.
+		b.(T).
+		c
+}
+
+// Don't introduce extra newlines in strangely formatted expression lists.
+func f() {
+	// os.Open parameters should remain on two lines
+	if writer, err = os.Open(outfile, s.O_WRONLY|os.O_CREATE|
+		os.O_TRUNC, 0666); err != nil {
+		log.Fatal(err)
+	}
+}
diff --git a/src/pkg/go/printer/testdata/linebreaks.golden b/src/pkg/go/printer/testdata/linebreaks.golden
new file mode 100644
index 000000000..be780da67
--- /dev/null
+++ b/src/pkg/go/printer/testdata/linebreaks.golden
@@ -0,0 +1,223 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package linebreaks
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+type writerTestEntry struct {
+	header		*Header
+	contents	string
+}
+
+type writerTest struct {
+	file	string	// filename of expected output
+	entries	[]*writerTestEntry
+}
+
+var writerTests = []*writerTest{
+	&writerTest{
+		file:	"testdata/writer.tar",
+		entries: []*writerTestEntry{
+			&writerTestEntry{
+				header: &Header{
+					Name:		"small.txt",
+					Mode:		0640,
+					Uid:		73025,
+					Gid:		5000,
+					Size:		5,
+					Mtime:		1246508266,
+					Typeflag:	'0',
+					Uname:		"dsymonds",
+					Gname:		"eng",
+				},
+				contents:	"Kilts",
+			},
+			&writerTestEntry{
+				header: &Header{
+					Name:		"small2.txt",
+					Mode:		0640,
+					Uid:		73025,
+					Gid:		5000,
+					Size:		11,
+					Mtime:		1245217492,
+					Typeflag:	'0',
+					Uname:		"dsymonds",
+					Gname:		"eng",
+				},
+				contents:	"Google.com\n",
+			},
+		},
+	},
+	// The truncated test file was produced using these commands:
+	//   dd if=/dev/zero bs=1048576 count=16384 > /tmp/16gig.txt
+	//   tar -b 1 -c -f- /tmp/16gig.txt | dd bs=512 count=8 > writer-big.tar
+	&writerTest{
+		file:	"testdata/writer-big.tar",
+		entries: []*writerTestEntry{
+			&writerTestEntry{
+				header: &Header{
+					Name:		"tmp/16gig.txt",
+					Mode:		0640,
+					Uid:		73025,
+					Gid:		5000,
+					Size:		16 << 30,
+					Mtime:		1254699560,
+					Typeflag:	'0',
+					Uname:		"dsymonds",
+					Gname:		"eng",
+				},
+				// no contents
+			},
+		},
+	},
+}
+
+type untarTest struct {
+	file	string
+	headers	[]*Header
+}
+
+var untarTests = []*untarTest{
+	&untarTest{
+		file:	"testdata/gnu.tar",
+		headers: []*Header{
+			&Header{
+				Name:		"small.txt",
+				Mode:		0640,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		5,
+				Mtime:		1244428340,
+				Typeflag:	'0',
+				Uname:		"dsymonds",
+				Gname:		"eng",
+			},
+			&Header{
+				Name:		"small2.txt",
+				Mode:		0640,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		11,
+				Mtime:		1244436044,
+				Typeflag:	'0',
+				Uname:		"dsymonds",
+				Gname:		"eng",
+			},
+		},
+	},
+	&untarTest{
+		file:	"testdata/star.tar",
+		headers: []*Header{
+			&Header{
+				Name:		"small.txt",
+				Mode:		0640,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		5,
+				Mtime:		1244592783,
+				Typeflag:	'0',
+				Uname:		"dsymonds",
+				Gname:		"eng",
+				Atime:		1244592783,
+				Ctime:		1244592783,
+			},
+			&Header{
+				Name:		"small2.txt",
+				Mode:		0640,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		11,
+				Mtime:		1244592783,
+				Typeflag:	'0',
+				Uname:		"dsymonds",
+				Gname:		"eng",
+				Atime:		1244592783,
+				Ctime:		1244592783,
+			},
+		},
+	},
+	&untarTest{
+		file:	"testdata/v7.tar",
+		headers: []*Header{
+			&Header{
+				Name:		"small.txt",
+				Mode:		0444,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		5,
+				Mtime:		1244593104,
+				Typeflag:	'\x00',
+			},
+			&Header{
+				Name:		"small2.txt",
+				Mode:		0444,
+				Uid:		73025,
+				Gid:		5000,
+				Size:		11,
+				Mtime:		1244593104,
+				Typeflag:	'\x00',
+			},
+		},
+	},
+}
+
+var facts = map[int]string{
+	0:	"1",
+	1:	"1",
+	2:	"2",
+	10:	"3628800",
+	20:	"2432902008176640000",
+	100: "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000",
+}
+
+func usage() {
+	fmt.Fprintf(os.Stderr,
+		// TODO(gri): the 2nd string of this string list should not be indented
+		"usage: godoc package [name ...]\n"+
+			"	godoc -http=:6060\n")
+	flag.PrintDefaults()
+	os.Exit(2)
+}
+
+func TestReader(t *testing.T) {
+testLoop:
+	for i, test := range untarTests {
+		f, err := os.Open(test.file, os.O_RDONLY, 0444)
+		if err != nil {
+			t.Errorf("test %d: Unexpected error: %v", i, err)
+			continue
+		}
+		tr := NewReader(f)
+		for j, header := range test.headers {
+			hdr, err := tr.Next()
+			if err != nil || hdr == nil {
+				t.Errorf("test %d, entry %d: Didn't get entry: %v", i, j, err)
+				f.Close()
+				continue testLoop
+			}
+			if !reflect.DeepEqual(hdr, header) {
+				t.Errorf("test %d, entry %d: Incorrect header:\nhave %+v\nwant %+v",
+					i, j, *hdr, *header)
+			}
+		}
+		hdr, err := tr.Next()
+		if hdr != nil || err != nil {
+			t.Errorf("test %d: Unexpected entry or error: hdr=%v err=%v", i, err)
+		}
+		f.Close()
+	}
+}
+
+// There should be exactly one linebreak after this comment.
diff --git a/src/pkg/go/printer/testdata/linebreaks.input b/src/pkg/go/printer/testdata/linebreaks.input
new file mode 100644
index 000000000..457b491e6
--- /dev/null
+++ b/src/pkg/go/printer/testdata/linebreaks.input
@@ -0,0 +1,223 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package linebreaks
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"strings"
+	"testing"
+)
+
+type writerTestEntry struct {
+	header *Header
+	contents string
+}
+
+type writerTest struct {
+	file string  // filename of expected output
+	entries []*writerTestEntry
+}
+
+var writerTests = []*writerTest{
+	&writerTest{
+		file: "testdata/writer.tar",
+		entries: []*writerTestEntry{
+			&writerTestEntry{
+				header: &Header{
+					Name: "small.txt",
+					Mode: 0640,
+					Uid: 73025,
+					Gid: 5000,
+					Size: 5,
+					Mtime: 1246508266,
+					Typeflag: '0',
+					Uname: "dsymonds",
+					Gname: "eng",
+				},
+				contents: "Kilts",
+			},
+			&writerTestEntry{
+				header: &Header{
+					Name: "small2.txt",
+					Mode: 0640,
+					Uid: 73025,
+					Gid: 5000,
+					Size: 11,
+					Mtime: 1245217492,
+					Typeflag: '0',
+					Uname: "dsymonds",
+					Gname: "eng",
+				},
+				contents: "Google.com\n",
+			},
+		},
+	},
+	// The truncated test file was produced using these commands:
+	//   dd if=/dev/zero bs=1048576 count=16384 > /tmp/16gig.txt
+	//   tar -b 1 -c -f- /tmp/16gig.txt | dd bs=512 count=8 > writer-big.tar
+	&writerTest{
+		file: "testdata/writer-big.tar",
+		entries: []*writerTestEntry{
+			&writerTestEntry{
+				header: &Header{
+					Name: "tmp/16gig.txt",
+					Mode: 0640,
+					Uid: 73025,
+					Gid: 5000,
+					Size: 16 << 30,
+					Mtime: 1254699560,
+					Typeflag: '0',
+					Uname: "dsymonds",
+					Gname: "eng",
+				},
+				// no contents
+			},
+		},
+	},
+}
+
+type untarTest struct {
+	file string
+	headers []*Header
+}
+
+var untarTests = []*untarTest{
+	&untarTest{
+		file: "testdata/gnu.tar",
+		headers: []*Header{
+			&Header{
+				Name: "small.txt",
+				Mode: 0640,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 5,
+				Mtime: 1244428340,
+				Typeflag: '0',
+				Uname: "dsymonds",
+				Gname: "eng",
+			},
+			&Header{
+				Name: "small2.txt",
+				Mode: 0640,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 11,
+				Mtime: 1244436044,
+				Typeflag: '0',
+				Uname: "dsymonds",
+				Gname: "eng",
+			},
+		},
+	},
+	&untarTest{
+		file: "testdata/star.tar",
+		headers: []*Header{
+			&Header{
+				Name: "small.txt",
+				Mode: 0640,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 5,
+				Mtime: 1244592783,
+				Typeflag: '0',
+				Uname: "dsymonds",
+				Gname: "eng",
+				Atime: 1244592783,
+				Ctime: 1244592783,
+			},
+			&Header{
+				Name: "small2.txt",
+				Mode: 0640,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 11,
+				Mtime: 1244592783,
+				Typeflag: '0',
+				Uname: "dsymonds",
+				Gname: "eng",
+				Atime: 1244592783,
+				Ctime: 1244592783,
+			},
+		},
+	},
+	&untarTest{
+		file: "testdata/v7.tar",
+		headers: []*Header{
+			&Header{
+				Name: "small.txt",
+				Mode: 0444,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 5,
+				Mtime: 1244593104,
+				Typeflag: '\x00',
+			},
+			&Header{
+				Name: "small2.txt",
+				Mode: 0444,
+				Uid: 73025,
+				Gid: 5000,
+				Size: 11,
+				Mtime: 1244593104,
+				Typeflag: '\x00',
+			},
+		},
+	},
+}
+
+var facts = map[int] string {
+	0: "1",
+	1: "1",
+	2: "2",
+	10: "3628800",
+	20: "2432902008176640000",
+	100: "933262154439441526816992388562667004907159682643816214685929" +
+		"638952175999932299156089414639761565182862536979208272237582" +
+		"51185210916864000000000000000000000000",
+}
+
+func usage() {
+	fmt.Fprintf(os.Stderr,
+		// TODO(gri): the 2nd string of this string list should not be indented
+		"usage: godoc package [name ...]\n" +
+		"	godoc -http=:6060\n")
+	flag.PrintDefaults()
+	os.Exit(2)
+}
+
+func TestReader(t *testing.T) {
+testLoop:
+	for i, test := range untarTests {
+		f, err := os.Open(test.file, os.O_RDONLY, 0444)
+		if err != nil {
+			t.Errorf("test %d: Unexpected error: %v", i, err)
+			continue
+		}
+		tr := NewReader(f)
+		for j, header := range test.headers {
+			hdr, err := tr.Next()
+			if err != nil || hdr == nil {
+				t.Errorf("test %d, entry %d: Didn't get entry: %v", i, j, err)
+				f.Close()
+				continue testLoop
+			}
+			if !reflect.DeepEqual(hdr, header) {
+				t.Errorf("test %d, entry %d: Incorrect header:\nhave %+v\nwant %+v",
+					 i, j, *hdr, *header)
+			}
+		}
+		hdr, err := tr.Next()
+		if hdr != nil || err != nil {
+			t.Errorf("test %d: Unexpected entry or error: hdr=%v err=%v", i, err)
+		}
+		f.Close()
+	}
+}
+
+// There should be exactly one linebreak after this comment.
diff --git a/src/pkg/go/printer/testdata/parser.go b/src/pkg/go/printer/testdata/parser.go
new file mode 100644
index 000000000..2d27af499
--- /dev/null
+++ b/src/pkg/go/printer/testdata/parser.go
@@ -0,0 +1,2153 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package parser implements a parser for Go source files. Input may be
+// provided in a variety of forms (see the various Parse* functions); the
+// output is an abstract syntax tree (AST) representing the Go source. The
+// parser is invoked through one of the Parse* functions.
+//
+package parser
+
+import (
+	"fmt"
+	"go/ast"
+	"go/scanner"
+	"go/token"
+)
+
+// The mode parameter to the Parse* functions is a set of flags (or 0).
+// They control the amount of source code parsed and other optional
+// parser functionality.
+//
+const (
+	PackageClauseOnly uint = 1 << iota // parsing stops after package clause
+	ImportsOnly                        // parsing stops after import declarations
+	ParseComments                      // parse comments and add them to AST
+	Trace                              // print a trace of parsed productions
+	DeclarationErrors                  // report declaration errors
+)
+
+// The parser structure holds the parser's internal state.
+type parser struct {
+	file *token.File
+	scanner.ErrorVector
+	scanner scanner.Scanner
+
+	// Tracing/debugging
+	mode   uint // parsing mode
+	trace  bool // == (mode & Trace != 0)
+	indent uint // indentation used for tracing output
+
+	// Comments
+	comments    []*ast.CommentGroup
+	leadComment *ast.CommentGroup // last lead comment
+	lineComment *ast.CommentGroup // last line comment
+
+	// Next token
+	pos token.Pos   // token position
+	tok token.Token // one token look-ahead
+	lit string      // token literal
+
+	// Non-syntactic parser control
+	exprLev int // < 0: in control clause, >= 0: in expression
+
+	// Ordinary identifer scopes
+	pkgScope   *ast.Scope        // pkgScope.Outer == nil
+	topScope   *ast.Scope        // top-most scope; may be pkgScope
+	unresolved []*ast.Ident      // unresolved identifiers
+	imports    []*ast.ImportSpec // list of imports
+
+	// Label scope
+	// (maintained by open/close LabelScope)
+	labelScope  *ast.Scope     // label scope for current function
+	targetStack [][]*ast.Ident // stack of unresolved labels
+}
+
+// scannerMode returns the scanner mode bits given the parser's mode bits.
+func scannerMode(mode uint) uint {
+	var m uint = scanner.InsertSemis
+	if mode&ParseComments != 0 {
+		m |= scanner.ScanComments
+	}
+	return m
+}
+
+func (p *parser) init(fset *token.FileSet, filename string, src []byte, mode uint) {
+	p.file = fset.AddFile(filename, fset.Base(), len(src))
+	p.scanner.Init(p.file, src, p, scannerMode(mode))
+
+	p.mode = mode
+	p.trace = mode&Trace != 0 // for convenience (p.trace is used frequently)
+
+	p.next()
+
+	// set up the pkgScope here (as opposed to in parseFile) because
+	// there are other parser entry points (ParseExpr, etc.)
+	p.openScope()
+	p.pkgScope = p.topScope
+
+	// for the same reason, set up a label scope
+	p.openLabelScope()
+}
+
+// ----------------------------------------------------------------------------
+// Scoping support
+
+func (p *parser) openScope() {
+	p.topScope = ast.NewScope(p.topScope)
+}
+
+func (p *parser) closeScope() {
+	p.topScope = p.topScope.Outer
+}
+
+func (p *parser) openLabelScope() {
+	p.labelScope = ast.NewScope(p.labelScope)
+	p.targetStack = append(p.targetStack, nil)
+}
+
+func (p *parser) closeLabelScope() {
+	// resolve labels
+	n := len(p.targetStack) - 1
+	scope := p.labelScope
+	for _, ident := range p.targetStack[n] {
+		ident.Obj = scope.Lookup(ident.Name)
+		if ident.Obj == nil && p.mode&DeclarationErrors != 0 {
+			p.error(ident.Pos(), fmt.Sprintf("label %s undefined", ident.Name))
+		}
+	}
+	// pop label scope
+	p.targetStack = p.targetStack[0:n]
+	p.labelScope = p.labelScope.Outer
+}
+
+func (p *parser) declare(decl interface{}, scope *ast.Scope, kind ast.ObjKind, idents ...*ast.Ident) {
+	for _, ident := range idents {
+		assert(ident.Obj == nil, "identifier already declared or resolved")
+		if ident.Name != "_" {
+			obj := ast.NewObj(kind, ident.Name)
+			// remember the corresponding declaration for redeclaration
+			// errors and global variable resolution/typechecking phase
+			obj.Decl = decl
+			if alt := scope.Insert(obj); alt != nil && p.mode&DeclarationErrors != 0 {
+				prevDecl := ""
+				if pos := alt.Pos(); pos.IsValid() {
+					prevDecl = fmt.Sprintf("\n\tprevious declaration at %s", p.file.Position(pos))
+				}
+				p.error(ident.Pos(), fmt.Sprintf("%s redeclared in this block%s", ident.Name, prevDecl))
+			}
+			ident.Obj = obj
+		}
+	}
+}
+
+func (p *parser) shortVarDecl(idents []*ast.Ident) {
+	// Go spec: A short variable declaration may redeclare variables
+	// provided they were originally declared in the same block with
+	// the same type, and at least one of the non-blank variables is new.
+	n := 0 // number of new variables
+	for _, ident := range idents {
+		assert(ident.Obj == nil, "identifier already declared or resolved")
+		if ident.Name != "_" {
+			obj := ast.NewObj(ast.Var, ident.Name)
+			// short var declarations cannot have redeclaration errors
+			// and are not global => no need to remember the respective
+			// declaration
+			alt := p.topScope.Insert(obj)
+			if alt == nil {
+				n++ // new declaration
+				alt = obj
+			}
+			ident.Obj = alt
+		}
+	}
+	if n == 0 && p.mode&DeclarationErrors != 0 {
+		p.error(idents[0].Pos(), "no new variables on left side of :=")
+	}
+}
+
+// The unresolved object is a sentinel to mark identifiers that have been added
+// to the list of unresolved identifiers. The sentinel is only used for verifying
+// internal consistency.
+var unresolved = new(ast.Object)
+
+func (p *parser) resolve(x ast.Expr) {
+	// nothing to do if x is not an identifier or the blank identifier
+	ident, _ := x.(*ast.Ident)
+	if ident == nil {
+		return
+	}
+	assert(ident.Obj == nil, "identifier already declared or resolved")
+	if ident.Name == "_" {
+		return
+	}
+	// try to resolve the identifier
+	for s := p.topScope; s != nil; s = s.Outer {
+		if obj := s.Lookup(ident.Name); obj != nil {
+			ident.Obj = obj
+			return
+		}
+	}
+	// all local scopes are known, so any unresolved identifier
+	// must be found either in the file scope, package scope
+	// (perhaps in another file), or universe scope --- collect
+	// them so that they can be resolved later
+	ident.Obj = unresolved
+	p.unresolved = append(p.unresolved, ident)
+}
+
+// ----------------------------------------------------------------------------
+// Parsing support
+
+func (p *parser) printTrace(a ...interface{}) {
+	const dots = ". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . " +
+		". . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . "
+	const n = uint(len(dots))
+	pos := p.file.Position(p.pos)
+	fmt.Printf("%5d:%3d: ", pos.Line, pos.Column)
+	i := 2 * p.indent
+	for ; i > n; i -= n {
+		fmt.Print(dots)
+	}
+	fmt.Print(dots[0:i])
+	fmt.Println(a...)
+}
+
+func trace(p *parser, msg string) *parser {
+	p.printTrace(msg, "(")
+	p.indent++
+	return p
+}
+
+// Usage pattern: defer un(trace(p, "..."));
+func un(p *parser) {
+	p.indent--
+	p.printTrace(")")
+}
+
+// Advance to the next token.
+func (p *parser) next0() {
+	// Because of one-token look-ahead, print the previous token
+	// when tracing as it provides a more readable output. The
+	// very first token (!p.pos.IsValid()) is not initialized
+	// (it is token.ILLEGAL), so don't print it .
+	if p.trace && p.pos.IsValid() {
+		s := p.tok.String()
+		switch {
+		case p.tok.IsLiteral():
+			p.printTrace(s, p.lit)
+		case p.tok.IsOperator(), p.tok.IsKeyword():
+			p.printTrace("\"" + s + "\"")
+		default:
+			p.printTrace(s)
+		}
+	}
+
+	p.pos, p.tok, p.lit = p.scanner.Scan()
+}
+
+// Consume a comment and return it and the line on which it ends.
+func (p *parser) consumeComment() (comment *ast.Comment, endline int) {
+	// /*-style comments may end on a different line than where they start.
+	// Scan the comment for '\n' chars and adjust endline accordingly.
+	endline = p.file.Line(p.pos)
+	if p.lit[1] == '*' {
+		// don't use range here - no need to decode Unicode code points
+		for i := 0; i < len(p.lit); i++ {
+			if p.lit[i] == '\n' {
+				endline++
+			}
+		}
+	}
+
+	comment = &ast.Comment{p.pos, p.lit}
+	p.next0()
+
+	return
+}
+
+// Consume a group of adjacent comments, add it to the parser's
+// comments list, and return it together with the line at which
+// the last comment in the group ends. An empty line or non-comment
+// token terminates a comment group.
+//
+func (p *parser) consumeCommentGroup() (comments *ast.CommentGroup, endline int) {
+	var list []*ast.Comment
+	endline = p.file.Line(p.pos)
+	for p.tok == token.COMMENT && endline+1 >= p.file.Line(p.pos) {
+		var comment *ast.Comment
+		comment, endline = p.consumeComment()
+		list = append(list, comment)
+	}
+
+	// add comment group to the comments list
+	comments = &ast.CommentGroup{list}
+	p.comments = append(p.comments, comments)
+
+	return
+}
+
+// Advance to the next non-comment token. In the process, collect
+// any comment groups encountered, and remember the last lead and
+// and line comments.
+//
+// A lead comment is a comment group that starts and ends in a
+// line without any other tokens and that is followed by a non-comment
+// token on the line immediately after the comment group.
+//
+// A line comment is a comment group that follows a non-comment
+// token on the same line, and that has no tokens after it on the line
+// where it ends.
+//
+// Lead and line comments may be considered documentation that is
+// stored in the AST.
+//
+func (p *parser) next() {
+	p.leadComment = nil
+	p.lineComment = nil
+	line := p.file.Line(p.pos) // current line
+	p.next0()
+
+	if p.tok == token.COMMENT {
+		var comment *ast.CommentGroup
+		var endline int
+
+		if p.file.Line(p.pos) == line {
+			// The comment is on same line as the previous token; it
+			// cannot be a lead comment but may be a line comment.
+			comment, endline = p.consumeCommentGroup()
+			if p.file.Line(p.pos) != endline {
+				// The next token is on a different line, thus
+				// the last comment group is a line comment.
+				p.lineComment = comment
+			}
+		}
+
+		// consume successor comments, if any
+		endline = -1
+		for p.tok == token.COMMENT {
+			comment, endline = p.consumeCommentGroup()
+		}
+
+		if endline+1 == p.file.Line(p.pos) {
+			// The next token is following on the line immediately after the
+			// comment group, thus the last comment group is a lead comment.
+			p.leadComment = comment
+		}
+	}
+}
+
+func (p *parser) error(pos token.Pos, msg string) {
+	p.Error(p.file.Position(pos), msg)
+}
+
+func (p *parser) errorExpected(pos token.Pos, msg string) {
+	msg = "expected " + msg
+	if pos == p.pos {
+		// the error happened at the current position;
+		// make the error message more specific
+		if p.tok == token.SEMICOLON && p.lit[0] == '\n' {
+			msg += ", found newline"
+		} else {
+			msg += ", found '" + p.tok.String() + "'"
+			if p.tok.IsLiteral() {
+				msg += " " + p.lit
+			}
+		}
+	}
+	p.error(pos, msg)
+}
+
+func (p *parser) expect(tok token.Token) token.Pos {
+	pos := p.pos
+	if p.tok != tok {
+		p.errorExpected(pos, "'"+tok.String()+"'")
+	}
+	p.next() // make progress
+	return pos
+}
+
+func (p *parser) expectSemi() {
+	if p.tok != token.RPAREN && p.tok != token.RBRACE {
+		p.expect(token.SEMICOLON)
+	}
+}
+
+func assert(cond bool, msg string) {
+	if !cond {
+		panic("go/parser internal error: " + msg)
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Identifiers
+
+func (p *parser) parseIdent() *ast.Ident {
+	pos := p.pos
+	name := "_"
+	if p.tok == token.IDENT {
+		name = p.lit
+		p.next()
+	} else {
+		p.expect(token.IDENT) // use expect() error handling
+	}
+	return &ast.Ident{pos, name, nil}
+}
+
+func (p *parser) parseIdentList() (list []*ast.Ident) {
+	if p.trace {
+		defer un(trace(p, "IdentList"))
+	}
+
+	list = append(list, p.parseIdent())
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.parseIdent())
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Common productions
+
+// If lhs is set, result list elements which are identifiers are not resolved.
+func (p *parser) parseExprList(lhs bool) (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "ExpressionList"))
+	}
+
+	list = append(list, p.parseExpr(lhs))
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.parseExpr(lhs))
+	}
+
+	return
+}
+
+func (p *parser) parseLhsList() []ast.Expr {
+	list := p.parseExprList(true)
+	switch p.tok {
+	case token.DEFINE:
+		// lhs of a short variable declaration
+		p.shortVarDecl(p.makeIdentList(list))
+	case token.COLON:
+		// lhs of a label declaration or a communication clause of a select
+		// statement (parseLhsList is not called when parsing the case clause
+		// of a switch statement):
+		// - labels are declared by the caller of parseLhsList
+		// - for communication clauses, if there is a stand-alone identifier
+		//   followed by a colon, we have a syntax error; there is no need
+		//   to resolve the identifier in that case
+	default:
+		// identifiers must be declared elsewhere
+		for _, x := range list {
+			p.resolve(x)
+		}
+	}
+	return list
+}
+
+func (p *parser) parseRhsList() []ast.Expr {
+	return p.parseExprList(false)
+}
+
+// ----------------------------------------------------------------------------
+// Types
+
+func (p *parser) parseType() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Type"))
+	}
+
+	typ := p.tryType()
+
+	if typ == nil {
+		pos := p.pos
+		p.errorExpected(pos, "type")
+		p.next() // make progress
+		return &ast.BadExpr{pos, p.pos}
+	}
+
+	return typ
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) parseTypeName() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeName"))
+	}
+
+	ident := p.parseIdent()
+	// don't resolve ident yet - it may be a parameter or field name
+
+	if p.tok == token.PERIOD {
+		// ident is a package name
+		p.next()
+		p.resolve(ident)
+		sel := p.parseIdent()
+		return &ast.SelectorExpr{ident, sel}
+	}
+
+	return ident
+}
+
+func (p *parser) parseArrayType(ellipsisOk bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "ArrayType"))
+	}
+
+	lbrack := p.expect(token.LBRACK)
+	var len ast.Expr
+	if ellipsisOk && p.tok == token.ELLIPSIS {
+		len = &ast.Ellipsis{p.pos, nil}
+		p.next()
+	} else if p.tok != token.RBRACK {
+		len = p.parseRhs()
+	}
+	p.expect(token.RBRACK)
+	elt := p.parseType()
+
+	return &ast.ArrayType{lbrack, len, elt}
+}
+
+func (p *parser) makeIdentList(list []ast.Expr) []*ast.Ident {
+	idents := make([]*ast.Ident, len(list))
+	for i, x := range list {
+		ident, isIdent := x.(*ast.Ident)
+		if !isIdent {
+			pos := x.(ast.Expr).Pos()
+			p.errorExpected(pos, "identifier")
+			ident = &ast.Ident{pos, "_", nil}
+		}
+		idents[i] = ident
+	}
+	return idents
+}
+
+func (p *parser) parseFieldDecl(scope *ast.Scope) *ast.Field {
+	if p.trace {
+		defer un(trace(p, "FieldDecl"))
+	}
+
+	doc := p.leadComment
+
+	// fields
+	list, typ := p.parseVarList(false)
+
+	// optional tag
+	var tag *ast.BasicLit
+	if p.tok == token.STRING {
+		tag = &ast.BasicLit{p.pos, p.tok, p.lit}
+		p.next()
+	}
+
+	// analyze case
+	var idents []*ast.Ident
+	if typ != nil {
+		// IdentifierList Type
+		idents = p.makeIdentList(list)
+	} else {
+		// ["*"] TypeName (AnonymousField)
+		typ = list[0] // we always have at least one element
+		p.resolve(typ)
+		if n := len(list); n > 1 || !isTypeName(deref(typ)) {
+			pos := typ.Pos()
+			p.errorExpected(pos, "anonymous field")
+			typ = &ast.BadExpr{pos, list[n-1].End()}
+		}
+	}
+
+	p.expectSemi() // call before accessing p.linecomment
+
+	field := &ast.Field{doc, idents, typ, tag, p.lineComment}
+	p.declare(field, scope, ast.Var, idents...)
+
+	return field
+}
+
+func (p *parser) parseStructType() *ast.StructType {
+	if p.trace {
+		defer un(trace(p, "StructType"))
+	}
+
+	pos := p.expect(token.STRUCT)
+	lbrace := p.expect(token.LBRACE)
+	scope := ast.NewScope(nil) // struct scope
+	var list []*ast.Field
+	for p.tok == token.IDENT || p.tok == token.MUL || p.tok == token.LPAREN {
+		// a field declaration cannot start with a '(' but we accept
+		// it here for more robust parsing and better error messages
+		// (parseFieldDecl will check and complain if necessary)
+		list = append(list, p.parseFieldDecl(scope))
+	}
+	rbrace := p.expect(token.RBRACE)
+
+	// TODO(gri): store struct scope in AST
+	return &ast.StructType{pos, &ast.FieldList{lbrace, list, rbrace}, false}
+}
+
+func (p *parser) parsePointerType() *ast.StarExpr {
+	if p.trace {
+		defer un(trace(p, "PointerType"))
+	}
+
+	star := p.expect(token.MUL)
+	base := p.parseType()
+
+	return &ast.StarExpr{star, base}
+}
+
+func (p *parser) tryVarType(isParam bool) ast.Expr {
+	if isParam && p.tok == token.ELLIPSIS {
+		pos := p.pos
+		p.next()
+		typ := p.tryIdentOrType(isParam) // don't use parseType so we can provide better error message
+		if typ == nil {
+			p.error(pos, "'...' parameter is missing type")
+			typ = &ast.BadExpr{pos, p.pos}
+		}
+		if p.tok != token.RPAREN {
+			p.error(pos, "can use '...' with last parameter type only")
+		}
+		return &ast.Ellipsis{pos, typ}
+	}
+	return p.tryIdentOrType(false)
+}
+
+func (p *parser) parseVarType(isParam bool) ast.Expr {
+	typ := p.tryVarType(isParam)
+	if typ == nil {
+		pos := p.pos
+		p.errorExpected(pos, "type")
+		p.next() // make progress
+		typ = &ast.BadExpr{pos, p.pos}
+	}
+	return typ
+}
+
+func (p *parser) parseVarList(isParam bool) (list []ast.Expr, typ ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "VarList"))
+	}
+
+	// a list of identifiers looks like a list of type names
+	for {
+		// parseVarType accepts any type (including parenthesized ones)
+		// even though the syntax does not permit them here: we
+		// accept them all for more robust parsing and complain
+		// afterwards
+		list = append(list, p.parseVarType(isParam))
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+	}
+
+	// if we had a list of identifiers, it must be followed by a type
+	typ = p.tryVarType(isParam)
+	if typ != nil {
+		p.resolve(typ)
+	}
+
+	return
+}
+
+func (p *parser) parseParameterList(scope *ast.Scope, ellipsisOk bool) (params []*ast.Field) {
+	if p.trace {
+		defer un(trace(p, "ParameterList"))
+	}
+
+	list, typ := p.parseVarList(ellipsisOk)
+	if typ != nil {
+		// IdentifierList Type
+		idents := p.makeIdentList(list)
+		field := &ast.Field{nil, idents, typ, nil, nil}
+		params = append(params, field)
+		// Go spec: The scope of an identifier denoting a function
+		// parameter or result variable is the function body.
+		p.declare(field, scope, ast.Var, idents...)
+		if p.tok == token.COMMA {
+			p.next()
+		}
+
+		for p.tok != token.RPAREN && p.tok != token.EOF {
+			idents := p.parseIdentList()
+			typ := p.parseVarType(ellipsisOk)
+			field := &ast.Field{nil, idents, typ, nil, nil}
+			params = append(params, field)
+			// Go spec: The scope of an identifier denoting a function
+			// parameter or result variable is the function body.
+			p.declare(field, scope, ast.Var, idents...)
+			if p.tok != token.COMMA {
+				break
+			}
+			p.next()
+		}
+
+	} else {
+		// Type { "," Type } (anonymous parameters)
+		params = make([]*ast.Field, len(list))
+		for i, x := range list {
+			p.resolve(x)
+			params[i] = &ast.Field{Type: x}
+		}
+	}
+
+	return
+}
+
+func (p *parser) parseParameters(scope *ast.Scope, ellipsisOk bool) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Parameters"))
+	}
+
+	var params []*ast.Field
+	lparen := p.expect(token.LPAREN)
+	if p.tok != token.RPAREN {
+		params = p.parseParameterList(scope, ellipsisOk)
+	}
+	rparen := p.expect(token.RPAREN)
+
+	return &ast.FieldList{lparen, params, rparen}
+}
+
+func (p *parser) parseResult(scope *ast.Scope) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Result"))
+	}
+
+	if p.tok == token.LPAREN {
+		return p.parseParameters(scope, false)
+	}
+
+	typ := p.tryType()
+	if typ != nil {
+		list := make([]*ast.Field, 1)
+		list[0] = &ast.Field{Type: typ}
+		return &ast.FieldList{List: list}
+	}
+
+	return nil
+}
+
+func (p *parser) parseSignature(scope *ast.Scope) (params, results *ast.FieldList) {
+	if p.trace {
+		defer un(trace(p, "Signature"))
+	}
+
+	params = p.parseParameters(scope, true)
+	results = p.parseResult(scope)
+
+	return
+}
+
+func (p *parser) parseFuncType() (*ast.FuncType, *ast.Scope) {
+	if p.trace {
+		defer un(trace(p, "FuncType"))
+	}
+
+	pos := p.expect(token.FUNC)
+	scope := ast.NewScope(p.topScope) // function scope
+	params, results := p.parseSignature(scope)
+
+	return &ast.FuncType{pos, params, results}, scope
+}
+
+func (p *parser) parseMethodSpec(scope *ast.Scope) *ast.Field {
+	if p.trace {
+		defer un(trace(p, "MethodSpec"))
+	}
+
+	doc := p.leadComment
+	var idents []*ast.Ident
+	var typ ast.Expr
+	x := p.parseTypeName()
+	if ident, isIdent := x.(*ast.Ident); isIdent && p.tok == token.LPAREN {
+		// method
+		idents = []*ast.Ident{ident}
+		scope := ast.NewScope(nil) // method scope
+		params, results := p.parseSignature(scope)
+		typ = &ast.FuncType{token.NoPos, params, results}
+	} else {
+		// embedded interface
+		typ = x
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	spec := &ast.Field{doc, idents, typ, nil, p.lineComment}
+	p.declare(spec, scope, ast.Fun, idents...)
+
+	return spec
+}
+
+func (p *parser) parseInterfaceType() *ast.InterfaceType {
+	if p.trace {
+		defer un(trace(p, "InterfaceType"))
+	}
+
+	pos := p.expect(token.INTERFACE)
+	lbrace := p.expect(token.LBRACE)
+	scope := ast.NewScope(nil) // interface scope
+	var list []*ast.Field
+	for p.tok == token.IDENT {
+		list = append(list, p.parseMethodSpec(scope))
+	}
+	rbrace := p.expect(token.RBRACE)
+
+	// TODO(gri): store interface scope in AST
+	return &ast.InterfaceType{pos, &ast.FieldList{lbrace, list, rbrace}, false}
+}
+
+func (p *parser) parseMapType() *ast.MapType {
+	if p.trace {
+		defer un(trace(p, "MapType"))
+	}
+
+	pos := p.expect(token.MAP)
+	p.expect(token.LBRACK)
+	key := p.parseType()
+	p.expect(token.RBRACK)
+	value := p.parseType()
+
+	return &ast.MapType{pos, key, value}
+}
+
+func (p *parser) parseChanType() *ast.ChanType {
+	if p.trace {
+		defer un(trace(p, "ChanType"))
+	}
+
+	pos := p.pos
+	dir := ast.SEND | ast.RECV
+	if p.tok == token.CHAN {
+		p.next()
+		if p.tok == token.ARROW {
+			p.next()
+			dir = ast.SEND
+		}
+	} else {
+		p.expect(token.ARROW)
+		p.expect(token.CHAN)
+		dir = ast.RECV
+	}
+	value := p.parseType()
+
+	return &ast.ChanType{pos, dir, value}
+}
+
+// If the result is an identifier, it is not resolved.
+func (p *parser) tryIdentOrType(ellipsisOk bool) ast.Expr {
+	switch p.tok {
+	case token.IDENT:
+		return p.parseTypeName()
+	case token.LBRACK:
+		return p.parseArrayType(ellipsisOk)
+	case token.STRUCT:
+		return p.parseStructType()
+	case token.MUL:
+		return p.parsePointerType()
+	case token.FUNC:
+		typ, _ := p.parseFuncType()
+		return typ
+	case token.INTERFACE:
+		return p.parseInterfaceType()
+	case token.MAP:
+		return p.parseMapType()
+	case token.CHAN, token.ARROW:
+		return p.parseChanType()
+	case token.LPAREN:
+		lparen := p.pos
+		p.next()
+		typ := p.parseType()
+		rparen := p.expect(token.RPAREN)
+		return &ast.ParenExpr{lparen, typ, rparen}
+	}
+
+	// no type found
+	return nil
+}
+
+func (p *parser) tryType() ast.Expr {
+	typ := p.tryIdentOrType(false)
+	if typ != nil {
+		p.resolve(typ)
+	}
+	return typ
+}
+
+// ----------------------------------------------------------------------------
+// Blocks
+
+func (p *parser) parseStmtList() (list []ast.Stmt) {
+	if p.trace {
+		defer un(trace(p, "StatementList"))
+	}
+
+	for p.tok != token.CASE && p.tok != token.DEFAULT && p.tok != token.RBRACE && p.tok != token.EOF {
+		list = append(list, p.parseStmt())
+	}
+
+	return
+}
+
+func (p *parser) parseBody(scope *ast.Scope) *ast.BlockStmt {
+	if p.trace {
+		defer un(trace(p, "Body"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	p.topScope = scope // open function scope
+	p.openLabelScope()
+	list := p.parseStmtList()
+	p.closeLabelScope()
+	p.closeScope()
+	rbrace := p.expect(token.RBRACE)
+
+	return &ast.BlockStmt{lbrace, list, rbrace}
+}
+
+func (p *parser) parseBlockStmt() *ast.BlockStmt {
+	if p.trace {
+		defer un(trace(p, "BlockStmt"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	p.openScope()
+	list := p.parseStmtList()
+	p.closeScope()
+	rbrace := p.expect(token.RBRACE)
+
+	return &ast.BlockStmt{lbrace, list, rbrace}
+}
+
+// ----------------------------------------------------------------------------
+// Expressions
+
+func (p *parser) parseFuncTypeOrLit() ast.Expr {
+	if p.trace {
+		defer un(trace(p, "FuncTypeOrLit"))
+	}
+
+	typ, scope := p.parseFuncType()
+	if p.tok != token.LBRACE {
+		// function type only
+		return typ
+	}
+
+	p.exprLev++
+	body := p.parseBody(scope)
+	p.exprLev--
+
+	return &ast.FuncLit{typ, body}
+}
+
+// parseOperand may return an expression or a raw type (incl. array
+// types of the form [...]T. Callers must verify the result.
+// If lhs is set and the result is an identifier, it is not resolved.
+//
+func (p *parser) parseOperand(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Operand"))
+	}
+
+	switch p.tok {
+	case token.IDENT:
+		x := p.parseIdent()
+		if !lhs {
+			p.resolve(x)
+		}
+		return x
+
+	case token.INT, token.FLOAT, token.IMAG, token.CHAR, token.STRING:
+		x := &ast.BasicLit{p.pos, p.tok, p.lit}
+		p.next()
+		return x
+
+	case token.LPAREN:
+		lparen := p.pos
+		p.next()
+		p.exprLev++
+		x := p.parseRhs()
+		p.exprLev--
+		rparen := p.expect(token.RPAREN)
+		return &ast.ParenExpr{lparen, x, rparen}
+
+	case token.FUNC:
+		return p.parseFuncTypeOrLit()
+
+	default:
+		if typ := p.tryIdentOrType(true); typ != nil {
+			// could be type for composite literal or conversion
+			_, isIdent := typ.(*ast.Ident)
+			assert(!isIdent, "type cannot be identifier")
+			return typ
+		}
+	}
+
+	pos := p.pos
+	p.errorExpected(pos, "operand")
+	p.next() // make progress
+	return &ast.BadExpr{pos, p.pos}
+}
+
+func (p *parser) parseSelector(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Selector"))
+	}
+
+	sel := p.parseIdent()
+
+	return &ast.SelectorExpr{x, sel}
+}
+
+func (p *parser) parseTypeAssertion(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "TypeAssertion"))
+	}
+
+	p.expect(token.LPAREN)
+	var typ ast.Expr
+	if p.tok == token.TYPE {
+		// type switch: typ == nil
+		p.next()
+	} else {
+		typ = p.parseType()
+	}
+	p.expect(token.RPAREN)
+
+	return &ast.TypeAssertExpr{x, typ}
+}
+
+func (p *parser) parseIndexOrSlice(x ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "IndexOrSlice"))
+	}
+
+	lbrack := p.expect(token.LBRACK)
+	p.exprLev++
+	var low, high ast.Expr
+	isSlice := false
+	if p.tok != token.COLON {
+		low = p.parseRhs()
+	}
+	if p.tok == token.COLON {
+		isSlice = true
+		p.next()
+		if p.tok != token.RBRACK {
+			high = p.parseRhs()
+		}
+	}
+	p.exprLev--
+	rbrack := p.expect(token.RBRACK)
+
+	if isSlice {
+		return &ast.SliceExpr{x, lbrack, low, high, rbrack}
+	}
+	return &ast.IndexExpr{x, lbrack, low, rbrack}
+}
+
+func (p *parser) parseCallOrConversion(fun ast.Expr) *ast.CallExpr {
+	if p.trace {
+		defer un(trace(p, "CallOrConversion"))
+	}
+
+	lparen := p.expect(token.LPAREN)
+	p.exprLev++
+	var list []ast.Expr
+	var ellipsis token.Pos
+	for p.tok != token.RPAREN && p.tok != token.EOF && !ellipsis.IsValid() {
+		list = append(list, p.parseRhs())
+		if p.tok == token.ELLIPSIS {
+			ellipsis = p.pos
+			p.next()
+		}
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+	}
+	p.exprLev--
+	rparen := p.expect(token.RPAREN)
+
+	return &ast.CallExpr{fun, lparen, list, ellipsis, rparen}
+}
+
+func (p *parser) parseElement(keyOk bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Element"))
+	}
+
+	if p.tok == token.LBRACE {
+		return p.parseLiteralValue(nil)
+	}
+
+	x := p.parseExpr(keyOk) // don't resolve if map key
+	if keyOk {
+		if p.tok == token.COLON {
+			colon := p.pos
+			p.next()
+			return &ast.KeyValueExpr{x, colon, p.parseElement(false)}
+		}
+		p.resolve(x) // not a map key
+	}
+
+	return x
+}
+
+func (p *parser) parseElementList() (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "ElementList"))
+	}
+
+	for p.tok != token.RBRACE && p.tok != token.EOF {
+		list = append(list, p.parseElement(true))
+		if p.tok != token.COMMA {
+			break
+		}
+		p.next()
+	}
+
+	return
+}
+
+func (p *parser) parseLiteralValue(typ ast.Expr) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "LiteralValue"))
+	}
+
+	lbrace := p.expect(token.LBRACE)
+	var elts []ast.Expr
+	p.exprLev++
+	if p.tok != token.RBRACE {
+		elts = p.parseElementList()
+	}
+	p.exprLev--
+	rbrace := p.expect(token.RBRACE)
+	return &ast.CompositeLit{typ, lbrace, elts, rbrace}
+}
+
+// checkExpr checks that x is an expression (and not a type).
+func (p *parser) checkExpr(x ast.Expr) ast.Expr {
+	switch t := unparen(x).(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.BasicLit:
+	case *ast.FuncLit:
+	case *ast.CompositeLit:
+	case *ast.ParenExpr:
+		panic("unreachable")
+	case *ast.SelectorExpr:
+	case *ast.IndexExpr:
+	case *ast.SliceExpr:
+	case *ast.TypeAssertExpr:
+		if t.Type == nil {
+			// the form X.(type) is only allowed in type switch expressions
+			p.errorExpected(x.Pos(), "expression")
+			x = &ast.BadExpr{x.Pos(), x.End()}
+		}
+	case *ast.CallExpr:
+	case *ast.StarExpr:
+	case *ast.UnaryExpr:
+		if t.Op == token.RANGE {
+			// the range operator is only allowed at the top of a for statement
+			p.errorExpected(x.Pos(), "expression")
+			x = &ast.BadExpr{x.Pos(), x.End()}
+		}
+	case *ast.BinaryExpr:
+	default:
+		// all other nodes are not proper expressions
+		p.errorExpected(x.Pos(), "expression")
+		x = &ast.BadExpr{x.Pos(), x.End()}
+	}
+	return x
+}
+
+// isTypeName returns true iff x is a (qualified) TypeName.
+func isTypeName(x ast.Expr) bool {
+	switch t := x.(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.SelectorExpr:
+		_, isIdent := t.X.(*ast.Ident)
+		return isIdent
+	default:
+		return false // all other nodes are not type names
+	}
+	return true
+}
+
+// isLiteralType returns true iff x is a legal composite literal type.
+func isLiteralType(x ast.Expr) bool {
+	switch t := x.(type) {
+	case *ast.BadExpr:
+	case *ast.Ident:
+	case *ast.SelectorExpr:
+		_, isIdent := t.X.(*ast.Ident)
+		return isIdent
+	case *ast.ArrayType:
+	case *ast.StructType:
+	case *ast.MapType:
+	default:
+		return false // all other nodes are not legal composite literal types
+	}
+	return true
+}
+
+// If x is of the form *T, deref returns T, otherwise it returns x.
+func deref(x ast.Expr) ast.Expr {
+	if p, isPtr := x.(*ast.StarExpr); isPtr {
+		x = p.X
+	}
+	return x
+}
+
+// If x is of the form (T), unparen returns unparen(T), otherwise it returns x.
+func unparen(x ast.Expr) ast.Expr {
+	if p, isParen := x.(*ast.ParenExpr); isParen {
+		x = unparen(p.X)
+	}
+	return x
+}
+
+// checkExprOrType checks that x is an expression or a type
+// (and not a raw type such as [...]T).
+//
+func (p *parser) checkExprOrType(x ast.Expr) ast.Expr {
+	switch t := unparen(x).(type) {
+	case *ast.ParenExpr:
+		panic("unreachable")
+	case *ast.UnaryExpr:
+		if t.Op == token.RANGE {
+			// the range operator is only allowed at the top of a for statement
+			p.errorExpected(x.Pos(), "expression")
+			x = &ast.BadExpr{x.Pos(), x.End()}
+		}
+	case *ast.ArrayType:
+		if len, isEllipsis := t.Len.(*ast.Ellipsis); isEllipsis {
+			p.error(len.Pos(), "expected array length, found '...'")
+			x = &ast.BadExpr{x.Pos(), x.End()}
+		}
+	}
+
+	// all other nodes are expressions or types
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parsePrimaryExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "PrimaryExpr"))
+	}
+
+	x := p.parseOperand(lhs)
+L:
+	for {
+		switch p.tok {
+		case token.PERIOD:
+			p.next()
+			if lhs {
+				p.resolve(x)
+			}
+			switch p.tok {
+			case token.IDENT:
+				x = p.parseSelector(p.checkExpr(x))
+			case token.LPAREN:
+				x = p.parseTypeAssertion(p.checkExpr(x))
+			default:
+				pos := p.pos
+				p.next() // make progress
+				p.errorExpected(pos, "selector or type assertion")
+				x = &ast.BadExpr{pos, p.pos}
+			}
+		case token.LBRACK:
+			if lhs {
+				p.resolve(x)
+			}
+			x = p.parseIndexOrSlice(p.checkExpr(x))
+		case token.LPAREN:
+			if lhs {
+				p.resolve(x)
+			}
+			x = p.parseCallOrConversion(p.checkExprOrType(x))
+		case token.LBRACE:
+			if isLiteralType(x) && (p.exprLev >= 0 || !isTypeName(x)) {
+				if lhs {
+					p.resolve(x)
+				}
+				x = p.parseLiteralValue(x)
+			} else {
+				break L
+			}
+		default:
+			break L
+		}
+		lhs = false // no need to try to resolve again
+	}
+
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parseUnaryExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "UnaryExpr"))
+	}
+
+	switch p.tok {
+	case token.ADD, token.SUB, token.NOT, token.XOR, token.AND, token.RANGE:
+		pos, op := p.pos, p.tok
+		p.next()
+		x := p.parseUnaryExpr(false)
+		return &ast.UnaryExpr{pos, op, p.checkExpr(x)}
+
+	case token.ARROW:
+		// channel type or receive expression
+		pos := p.pos
+		p.next()
+		if p.tok == token.CHAN {
+			p.next()
+			value := p.parseType()
+			return &ast.ChanType{pos, ast.RECV, value}
+		}
+
+		x := p.parseUnaryExpr(false)
+		return &ast.UnaryExpr{pos, token.ARROW, p.checkExpr(x)}
+
+	case token.MUL:
+		// pointer type or unary "*" expression
+		pos := p.pos
+		p.next()
+		x := p.parseUnaryExpr(false)
+		return &ast.StarExpr{pos, p.checkExprOrType(x)}
+	}
+
+	return p.parsePrimaryExpr(lhs)
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+func (p *parser) parseBinaryExpr(lhs bool, prec1 int) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "BinaryExpr"))
+	}
+
+	x := p.parseUnaryExpr(lhs)
+	for prec := p.tok.Precedence(); prec >= prec1; prec-- {
+		for p.tok.Precedence() == prec {
+			pos, op := p.pos, p.tok
+			p.next()
+			if lhs {
+				p.resolve(x)
+				lhs = false
+			}
+			y := p.parseBinaryExpr(false, prec+1)
+			x = &ast.BinaryExpr{p.checkExpr(x), pos, op, p.checkExpr(y)}
+		}
+	}
+
+	return x
+}
+
+// If lhs is set and the result is an identifier, it is not resolved.
+// TODO(gri): parseExpr may return a type or even a raw type ([..]int) -
+//            should reject when a type/raw type is obviously not allowed
+func (p *parser) parseExpr(lhs bool) ast.Expr {
+	if p.trace {
+		defer un(trace(p, "Expression"))
+	}
+
+	return p.parseBinaryExpr(lhs, token.LowestPrec+1)
+}
+
+func (p *parser) parseRhs() ast.Expr {
+	return p.parseExpr(false)
+}
+
+// ----------------------------------------------------------------------------
+// Statements
+
+func (p *parser) parseSimpleStmt(labelOk bool) ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "SimpleStmt"))
+	}
+
+	x := p.parseLhsList()
+
+	switch p.tok {
+	case
+		token.DEFINE, token.ASSIGN, token.ADD_ASSIGN,
+		token.SUB_ASSIGN, token.MUL_ASSIGN, token.QUO_ASSIGN,
+		token.REM_ASSIGN, token.AND_ASSIGN, token.OR_ASSIGN,
+		token.XOR_ASSIGN, token.SHL_ASSIGN, token.SHR_ASSIGN, token.AND_NOT_ASSIGN:
+		// assignment statement
+		pos, tok := p.pos, p.tok
+		p.next()
+		y := p.parseRhsList()
+		return &ast.AssignStmt{x, pos, tok, y}
+	}
+
+	if len(x) > 1 {
+		p.errorExpected(x[0].Pos(), "1 expression")
+		// continue with first expression
+	}
+
+	switch p.tok {
+	case token.COLON:
+		// labeled statement
+		colon := p.pos
+		p.next()
+		if label, isIdent := x[0].(*ast.Ident); labelOk && isIdent {
+			// Go spec: The scope of a label is the body of the function
+			// in which it is declared and excludes the body of any nested
+			// function.
+			stmt := &ast.LabeledStmt{label, colon, p.parseStmt()}
+			p.declare(stmt, p.labelScope, ast.Lbl, label)
+			return stmt
+		}
+		p.error(x[0].Pos(), "illegal label declaration")
+		return &ast.BadStmt{x[0].Pos(), colon + 1}
+
+	case token.ARROW:
+		// send statement
+		arrow := p.pos
+		p.next() // consume "<-"
+		y := p.parseRhs()
+		return &ast.SendStmt{x[0], arrow, y}
+
+	case token.INC, token.DEC:
+		// increment or decrement
+		s := &ast.IncDecStmt{x[0], p.pos, p.tok}
+		p.next() // consume "++" or "--"
+		return s
+	}
+
+	// expression
+	return &ast.ExprStmt{x[0]}
+}
+
+func (p *parser) parseCallExpr() *ast.CallExpr {
+	x := p.parseRhs()
+	if call, isCall := x.(*ast.CallExpr); isCall {
+		return call
+	}
+	p.errorExpected(x.Pos(), "function/method call")
+	return nil
+}
+
+func (p *parser) parseGoStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "GoStmt"))
+	}
+
+	pos := p.expect(token.GO)
+	call := p.parseCallExpr()
+	p.expectSemi()
+	if call == nil {
+		return &ast.BadStmt{pos, pos + 2} // len("go")
+	}
+
+	return &ast.GoStmt{pos, call}
+}
+
+func (p *parser) parseDeferStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "DeferStmt"))
+	}
+
+	pos := p.expect(token.DEFER)
+	call := p.parseCallExpr()
+	p.expectSemi()
+	if call == nil {
+		return &ast.BadStmt{pos, pos + 5} // len("defer")
+	}
+
+	return &ast.DeferStmt{pos, call}
+}
+
+func (p *parser) parseReturnStmt() *ast.ReturnStmt {
+	if p.trace {
+		defer un(trace(p, "ReturnStmt"))
+	}
+
+	pos := p.pos
+	p.expect(token.RETURN)
+	var x []ast.Expr
+	if p.tok != token.SEMICOLON && p.tok != token.RBRACE {
+		x = p.parseRhsList()
+	}
+	p.expectSemi()
+
+	return &ast.ReturnStmt{pos, x}
+}
+
+func (p *parser) parseBranchStmt(tok token.Token) *ast.BranchStmt {
+	if p.trace {
+		defer un(trace(p, "BranchStmt"))
+	}
+
+	pos := p.expect(tok)
+	var label *ast.Ident
+	if tok != token.FALLTHROUGH && p.tok == token.IDENT {
+		label = p.parseIdent()
+		// add to list of unresolved targets
+		n := len(p.targetStack) - 1
+		p.targetStack[n] = append(p.targetStack[n], label)
+	}
+	p.expectSemi()
+
+	return &ast.BranchStmt{pos, tok, label}
+}
+
+func (p *parser) makeExpr(s ast.Stmt) ast.Expr {
+	if s == nil {
+		return nil
+	}
+	if es, isExpr := s.(*ast.ExprStmt); isExpr {
+		return p.checkExpr(es.X)
+	}
+	p.error(s.Pos(), "expected condition, found simple statement")
+	return &ast.BadExpr{s.Pos(), s.End()}
+}
+
+func (p *parser) parseIfStmt() *ast.IfStmt {
+	if p.trace {
+		defer un(trace(p, "IfStmt"))
+	}
+
+	pos := p.expect(token.IF)
+	p.openScope()
+	defer p.closeScope()
+
+	var s ast.Stmt
+	var x ast.Expr
+	{
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok == token.SEMICOLON {
+			p.next()
+			x = p.parseRhs()
+		} else {
+			s = p.parseSimpleStmt(false)
+			if p.tok == token.SEMICOLON {
+				p.next()
+				x = p.parseRhs()
+			} else {
+				x = p.makeExpr(s)
+				s = nil
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	body := p.parseBlockStmt()
+	var else_ ast.Stmt
+	if p.tok == token.ELSE {
+		p.next()
+		else_ = p.parseStmt()
+	} else {
+		p.expectSemi()
+	}
+
+	return &ast.IfStmt{pos, s, x, body, else_}
+}
+
+func (p *parser) parseTypeList() (list []ast.Expr) {
+	if p.trace {
+		defer un(trace(p, "TypeList"))
+	}
+
+	list = append(list, p.parseType())
+	for p.tok == token.COMMA {
+		p.next()
+		list = append(list, p.parseType())
+	}
+
+	return
+}
+
+func (p *parser) parseCaseClause(exprSwitch bool) *ast.CaseClause {
+	if p.trace {
+		defer un(trace(p, "CaseClause"))
+	}
+
+	pos := p.pos
+	var list []ast.Expr
+	if p.tok == token.CASE {
+		p.next()
+		if exprSwitch {
+			list = p.parseRhsList()
+		} else {
+			list = p.parseTypeList()
+		}
+	} else {
+		p.expect(token.DEFAULT)
+	}
+
+	colon := p.expect(token.COLON)
+	p.openScope()
+	body := p.parseStmtList()
+	p.closeScope()
+
+	return &ast.CaseClause{pos, list, colon, body}
+}
+
+func isExprSwitch(s ast.Stmt) bool {
+	if s == nil {
+		return true
+	}
+	if e, ok := s.(*ast.ExprStmt); ok {
+		if a, ok := e.X.(*ast.TypeAssertExpr); ok {
+			return a.Type != nil // regular type assertion
+		}
+		return true
+	}
+	return false
+}
+
+func (p *parser) parseSwitchStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "SwitchStmt"))
+	}
+
+	pos := p.expect(token.SWITCH)
+	p.openScope()
+	defer p.closeScope()
+
+	var s1, s2 ast.Stmt
+	if p.tok != token.LBRACE {
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok != token.SEMICOLON {
+			s2 = p.parseSimpleStmt(false)
+		}
+		if p.tok == token.SEMICOLON {
+			p.next()
+			s1 = s2
+			s2 = nil
+			if p.tok != token.LBRACE {
+				s2 = p.parseSimpleStmt(false)
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	exprSwitch := isExprSwitch(s2)
+	lbrace := p.expect(token.LBRACE)
+	var list []ast.Stmt
+	for p.tok == token.CASE || p.tok == token.DEFAULT {
+		list = append(list, p.parseCaseClause(exprSwitch))
+	}
+	rbrace := p.expect(token.RBRACE)
+	p.expectSemi()
+	body := &ast.BlockStmt{lbrace, list, rbrace}
+
+	if exprSwitch {
+		return &ast.SwitchStmt{pos, s1, p.makeExpr(s2), body}
+	}
+	// type switch
+	// TODO(gri): do all the checks!
+	return &ast.TypeSwitchStmt{pos, s1, s2, body}
+}
+
+func (p *parser) parseCommClause() *ast.CommClause {
+	if p.trace {
+		defer un(trace(p, "CommClause"))
+	}
+
+	p.openScope()
+	pos := p.pos
+	var comm ast.Stmt
+	if p.tok == token.CASE {
+		p.next()
+		lhs := p.parseLhsList()
+		if p.tok == token.ARROW {
+			// SendStmt
+			if len(lhs) > 1 {
+				p.errorExpected(lhs[0].Pos(), "1 expression")
+				// continue with first expression
+			}
+			arrow := p.pos
+			p.next()
+			rhs := p.parseRhs()
+			comm = &ast.SendStmt{lhs[0], arrow, rhs}
+		} else {
+			// RecvStmt
+			pos := p.pos
+			tok := p.tok
+			var rhs ast.Expr
+			if tok == token.ASSIGN || tok == token.DEFINE {
+				// RecvStmt with assignment
+				if len(lhs) > 2 {
+					p.errorExpected(lhs[0].Pos(), "1 or 2 expressions")
+					// continue with first two expressions
+					lhs = lhs[0:2]
+				}
+				p.next()
+				rhs = p.parseRhs()
+			} else {
+				// rhs must be single receive operation
+				if len(lhs) > 1 {
+					p.errorExpected(lhs[0].Pos(), "1 expression")
+					// continue with first expression
+				}
+				rhs = lhs[0]
+				lhs = nil // there is no lhs
+			}
+			if x, isUnary := rhs.(*ast.UnaryExpr); !isUnary || x.Op != token.ARROW {
+				p.errorExpected(rhs.Pos(), "send or receive operation")
+				rhs = &ast.BadExpr{rhs.Pos(), rhs.End()}
+			}
+			if lhs != nil {
+				comm = &ast.AssignStmt{lhs, pos, tok, []ast.Expr{rhs}}
+			} else {
+				comm = &ast.ExprStmt{rhs}
+			}
+		}
+	} else {
+		p.expect(token.DEFAULT)
+	}
+
+	colon := p.expect(token.COLON)
+	body := p.parseStmtList()
+	p.closeScope()
+
+	return &ast.CommClause{pos, comm, colon, body}
+}
+
+func (p *parser) parseSelectStmt() *ast.SelectStmt {
+	if p.trace {
+		defer un(trace(p, "SelectStmt"))
+	}
+
+	pos := p.expect(token.SELECT)
+	lbrace := p.expect(token.LBRACE)
+	var list []ast.Stmt
+	for p.tok == token.CASE || p.tok == token.DEFAULT {
+		list = append(list, p.parseCommClause())
+	}
+	rbrace := p.expect(token.RBRACE)
+	p.expectSemi()
+	body := &ast.BlockStmt{lbrace, list, rbrace}
+
+	return &ast.SelectStmt{pos, body}
+}
+
+func (p *parser) parseForStmt() ast.Stmt {
+	if p.trace {
+		defer un(trace(p, "ForStmt"))
+	}
+
+	pos := p.expect(token.FOR)
+	p.openScope()
+	defer p.closeScope()
+
+	var s1, s2, s3 ast.Stmt
+	if p.tok != token.LBRACE {
+		prevLev := p.exprLev
+		p.exprLev = -1
+		if p.tok != token.SEMICOLON {
+			s2 = p.parseSimpleStmt(false)
+		}
+		if p.tok == token.SEMICOLON {
+			p.next()
+			s1 = s2
+			s2 = nil
+			if p.tok != token.SEMICOLON {
+				s2 = p.parseSimpleStmt(false)
+			}
+			p.expectSemi()
+			if p.tok != token.LBRACE {
+				s3 = p.parseSimpleStmt(false)
+			}
+		}
+		p.exprLev = prevLev
+	}
+
+	body := p.parseBlockStmt()
+	p.expectSemi()
+
+	if as, isAssign := s2.(*ast.AssignStmt); isAssign {
+		// possibly a for statement with a range clause; check assignment operator
+		if as.Tok != token.ASSIGN && as.Tok != token.DEFINE {
+			p.errorExpected(as.TokPos, "'=' or ':='")
+			return &ast.BadStmt{pos, body.End()}
+		}
+		// check lhs
+		var key, value ast.Expr
+		switch len(as.Lhs) {
+		case 2:
+			key, value = as.Lhs[0], as.Lhs[1]
+		case 1:
+			key = as.Lhs[0]
+		default:
+			p.errorExpected(as.Lhs[0].Pos(), "1 or 2 expressions")
+			return &ast.BadStmt{pos, body.End()}
+		}
+		// check rhs
+		if len(as.Rhs) != 1 {
+			p.errorExpected(as.Rhs[0].Pos(), "1 expression")
+			return &ast.BadStmt{pos, body.End()}
+		}
+		if rhs, isUnary := as.Rhs[0].(*ast.UnaryExpr); isUnary && rhs.Op == token.RANGE {
+			// rhs is range expression
+			// (any short variable declaration was handled by parseSimpleStat above)
+			return &ast.RangeStmt{pos, key, value, as.TokPos, as.Tok, rhs.X, body}
+		}
+		p.errorExpected(s2.Pos(), "range clause")
+		return &ast.BadStmt{pos, body.End()}
+	}
+
+	// regular for statement
+	return &ast.ForStmt{pos, s1, p.makeExpr(s2), s3, body}
+}
+
+func (p *parser) parseStmt() (s ast.Stmt) {
+	if p.trace {
+		defer un(trace(p, "Statement"))
+	}
+
+	switch p.tok {
+	case token.CONST, token.TYPE, token.VAR:
+		s = &ast.DeclStmt{p.parseDecl()}
+	case
+		// tokens that may start a top-level expression
+		token.IDENT, token.INT, token.FLOAT, token.CHAR, token.STRING, token.FUNC, token.LPAREN, // operand
+		token.LBRACK, token.STRUCT, // composite type
+		token.MUL, token.AND, token.ARROW, token.ADD, token.SUB, token.XOR: // unary operators
+		s = p.parseSimpleStmt(true)
+		// because of the required look-ahead, labeled statements are
+		// parsed by parseSimpleStmt - don't expect a semicolon after
+		// them
+		if _, isLabeledStmt := s.(*ast.LabeledStmt); !isLabeledStmt {
+			p.expectSemi()
+		}
+	case token.GO:
+		s = p.parseGoStmt()
+	case token.DEFER:
+		s = p.parseDeferStmt()
+	case token.RETURN:
+		s = p.parseReturnStmt()
+	case token.BREAK, token.CONTINUE, token.GOTO, token.FALLTHROUGH:
+		s = p.parseBranchStmt(p.tok)
+	case token.LBRACE:
+		s = p.parseBlockStmt()
+		p.expectSemi()
+	case token.IF:
+		s = p.parseIfStmt()
+	case token.SWITCH:
+		s = p.parseSwitchStmt()
+	case token.SELECT:
+		s = p.parseSelectStmt()
+	case token.FOR:
+		s = p.parseForStmt()
+	case token.SEMICOLON:
+		s = &ast.EmptyStmt{p.pos}
+		p.next()
+	case token.RBRACE:
+		// a semicolon may be omitted before a closing "}"
+		s = &ast.EmptyStmt{p.pos}
+	default:
+		// no statement found
+		pos := p.pos
+		p.errorExpected(pos, "statement")
+		p.next() // make progress
+		s = &ast.BadStmt{pos, p.pos}
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Declarations
+
+type parseSpecFunction func(p *parser, doc *ast.CommentGroup, iota int) ast.Spec
+
+func parseImportSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "ImportSpec"))
+	}
+
+	var ident *ast.Ident
+	switch p.tok {
+	case token.PERIOD:
+		ident = &ast.Ident{p.pos, ".", nil}
+		p.next()
+	case token.IDENT:
+		ident = p.parseIdent()
+	}
+
+	var path *ast.BasicLit
+	if p.tok == token.STRING {
+		path = &ast.BasicLit{p.pos, p.tok, p.lit}
+		p.next()
+	} else {
+		p.expect(token.STRING) // use expect() error handling
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	// collect imports
+	spec := &ast.ImportSpec{doc, ident, path, p.lineComment}
+	p.imports = append(p.imports, spec)
+
+	return spec
+}
+
+func parseConstSpec(p *parser, doc *ast.CommentGroup, iota int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "ConstSpec"))
+	}
+
+	idents := p.parseIdentList()
+	typ := p.tryType()
+	var values []ast.Expr
+	if typ != nil || p.tok == token.ASSIGN || iota == 0 {
+		p.expect(token.ASSIGN)
+		values = p.parseRhsList()
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	// Go spec: The scope of a constant or variable identifier declared inside
+	// a function begins at the end of the ConstSpec or VarSpec and ends at
+	// the end of the innermost containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.ValueSpec{doc, idents, typ, values, p.lineComment}
+	p.declare(spec, p.topScope, ast.Con, idents...)
+
+	return spec
+}
+
+func parseTypeSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "TypeSpec"))
+	}
+
+	ident := p.parseIdent()
+
+	// Go spec: The scope of a type identifier declared inside a function begins
+	// at the identifier in the TypeSpec and ends at the end of the innermost
+	// containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.TypeSpec{doc, ident, nil, nil}
+	p.declare(spec, p.topScope, ast.Typ, ident)
+
+	spec.Type = p.parseType()
+	p.expectSemi() // call before accessing p.linecomment
+	spec.Comment = p.lineComment
+
+	return spec
+}
+
+func parseVarSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+	if p.trace {
+		defer un(trace(p, "VarSpec"))
+	}
+
+	idents := p.parseIdentList()
+	typ := p.tryType()
+	var values []ast.Expr
+	if typ == nil || p.tok == token.ASSIGN {
+		p.expect(token.ASSIGN)
+		values = p.parseRhsList()
+	}
+	p.expectSemi() // call before accessing p.linecomment
+
+	// Go spec: The scope of a constant or variable identifier declared inside
+	// a function begins at the end of the ConstSpec or VarSpec and ends at
+	// the end of the innermost containing block.
+	// (Global identifiers are resolved in a separate phase after parsing.)
+	spec := &ast.ValueSpec{doc, idents, typ, values, p.lineComment}
+	p.declare(spec, p.topScope, ast.Var, idents...)
+
+	return spec
+}
+
+func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction) *ast.GenDecl {
+	if p.trace {
+		defer un(trace(p, "GenDecl("+keyword.String()+")"))
+	}
+
+	doc := p.leadComment
+	pos := p.expect(keyword)
+	var lparen, rparen token.Pos
+	var list []ast.Spec
+	if p.tok == token.LPAREN {
+		lparen = p.pos
+		p.next()
+		for iota := 0; p.tok != token.RPAREN && p.tok != token.EOF; iota++ {
+			list = append(list, f(p, p.leadComment, iota))
+		}
+		rparen = p.expect(token.RPAREN)
+		p.expectSemi()
+	} else {
+		list = append(list, f(p, nil, 0))
+	}
+
+	return &ast.GenDecl{doc, pos, keyword, lparen, list, rparen}
+}
+
+func (p *parser) parseReceiver(scope *ast.Scope) *ast.FieldList {
+	if p.trace {
+		defer un(trace(p, "Receiver"))
+	}
+
+	pos := p.pos
+	par := p.parseParameters(scope, false)
+
+	// must have exactly one receiver
+	if par.NumFields() != 1 {
+		p.errorExpected(pos, "exactly one receiver")
+		// TODO determine a better range for BadExpr below
+		par.List = []*ast.Field{&ast.Field{Type: &ast.BadExpr{pos, pos}}}
+		return par
+	}
+
+	// recv type must be of the form ["*"] identifier
+	recv := par.List[0]
+	base := deref(recv.Type)
+	if _, isIdent := base.(*ast.Ident); !isIdent {
+		p.errorExpected(base.Pos(), "(unqualified) identifier")
+		par.List = []*ast.Field{&ast.Field{Type: &ast.BadExpr{recv.Pos(), recv.End()}}}
+	}
+
+	return par
+}
+
+func (p *parser) parseFuncDecl() *ast.FuncDecl {
+	if p.trace {
+		defer un(trace(p, "FunctionDecl"))
+	}
+
+	doc := p.leadComment
+	pos := p.expect(token.FUNC)
+	scope := ast.NewScope(p.topScope) // function scope
+
+	var recv *ast.FieldList
+	if p.tok == token.LPAREN {
+		recv = p.parseReceiver(scope)
+	}
+
+	ident := p.parseIdent()
+
+	params, results := p.parseSignature(scope)
+
+	var body *ast.BlockStmt
+	if p.tok == token.LBRACE {
+		body = p.parseBody(scope)
+	}
+	p.expectSemi()
+
+	decl := &ast.FuncDecl{doc, recv, ident, &ast.FuncType{pos, params, results}, body}
+	if recv == nil {
+		// Go spec: The scope of an identifier denoting a constant, type,
+		// variable, or function (but not method) declared at top level
+		// (outside any function) is the package block.
+		//
+		// init() functions cannot be referred to and there may
+		// be more than one - don't put them in the pkgScope
+		if ident.Name != "init" {
+			p.declare(decl, p.pkgScope, ast.Fun, ident)
+		}
+	}
+
+	return decl
+}
+
+func (p *parser) parseDecl() ast.Decl {
+	if p.trace {
+		defer un(trace(p, "Declaration"))
+	}
+
+	var f parseSpecFunction
+	switch p.tok {
+	case token.CONST:
+		f = parseConstSpec
+
+	case token.TYPE:
+		f = parseTypeSpec
+
+	case token.VAR:
+		f = parseVarSpec
+
+	case token.FUNC:
+		return p.parseFuncDecl()
+
+	default:
+		pos := p.pos
+		p.errorExpected(pos, "declaration")
+		p.next() // make progress
+		decl := &ast.BadDecl{pos, p.pos}
+		return decl
+	}
+
+	return p.parseGenDecl(p.tok, f)
+}
+
+func (p *parser) parseDeclList() (list []ast.Decl) {
+	if p.trace {
+		defer un(trace(p, "DeclList"))
+	}
+
+	for p.tok != token.EOF {
+		list = append(list, p.parseDecl())
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Source files
+
+func (p *parser) parseFile() *ast.File {
+	if p.trace {
+		defer un(trace(p, "File"))
+	}
+
+	// package clause
+	doc := p.leadComment
+	pos := p.expect(token.PACKAGE)
+	// Go spec: The package clause is not a declaration;
+	// the package name does not appear in any scope.
+	ident := p.parseIdent()
+	if ident.Name == "_" {
+		p.error(p.pos, "invalid package name _")
+	}
+	p.expectSemi()
+
+	var decls []ast.Decl
+
+	// Don't bother parsing the rest if we had errors already.
+	// Likely not a Go source file at all.
+
+	if p.ErrorCount() == 0 && p.mode&PackageClauseOnly == 0 {
+		// import decls
+		for p.tok == token.IMPORT {
+			decls = append(decls, p.parseGenDecl(token.IMPORT, parseImportSpec))
+		}
+
+		if p.mode&ImportsOnly == 0 {
+			// rest of package body
+			for p.tok != token.EOF {
+				decls = append(decls, p.parseDecl())
+			}
+		}
+	}
+
+	assert(p.topScope == p.pkgScope, "imbalanced scopes")
+
+	// resolve global identifiers within the same file
+	i := 0
+	for _, ident := range p.unresolved {
+		// i <= index for current ident
+		assert(ident.Obj == unresolved, "object already resolved")
+		ident.Obj = p.pkgScope.Lookup(ident.Name) // also removes unresolved sentinel
+		if ident.Obj == nil {
+			p.unresolved[i] = ident
+			i++
+		}
+	}
+
+	// TODO(gri): store p.imports in AST
+	return &ast.File{doc, pos, ident, decls, p.pkgScope, p.imports, p.unresolved[0:i], p.comments}
+}
diff --git a/src/pkg/go/printer/testdata/slow.golden b/src/pkg/go/printer/testdata/slow.golden
new file mode 100644
index 000000000..43a15cb1d
--- /dev/null
+++ b/src/pkg/go/printer/testdata/slow.golden
@@ -0,0 +1,85 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package deepequal_test
+
+import (
+	"testing"
+	"google3/spam/archer/frontend/deepequal"
+)
+
+func TestTwoNilValues(t *testing.T) {
+	if err := deepequal.Check(nil, nil); err != nil {
+		t.Errorf("expected nil, saw %v", err)
+	}
+}
+
+type Foo struct {
+	bar	*Bar
+	bang	*Bar
+}
+
+type Bar struct {
+	baz	*Baz
+	foo	[]*Foo
+}
+
+type Baz struct {
+	entries		map[int]interface{}
+	whatever	string
+}
+
+func newFoo() *Foo {
+	return &Foo{bar: &Bar{baz: &Baz{
+		entries: map[int]interface{}{
+			42:	&Foo{},
+			21:	&Bar{},
+			11:	&Baz{whatever: "it's just a test"}}}},
+		bang: &Bar{foo: []*Foo{
+			&Foo{bar: &Bar{baz: &Baz{
+				entries: map[int]interface{}{
+					43:	&Foo{},
+					22:	&Bar{},
+					13:	&Baz{whatever: "this is nuts"}}}},
+				bang: &Bar{foo: []*Foo{
+					&Foo{bar: &Bar{baz: &Baz{
+						entries: map[int]interface{}{
+							61:	&Foo{},
+							71:	&Bar{},
+							11:	&Baz{whatever: "no, it's Go"}}}},
+						bang: &Bar{foo: []*Foo{
+							&Foo{bar: &Bar{baz: &Baz{
+								entries: map[int]interface{}{
+									0:	&Foo{},
+									-2:	&Bar{},
+									-11:	&Baz{whatever: "we need to go deeper"}}}},
+								bang: &Bar{foo: []*Foo{
+									&Foo{bar: &Bar{baz: &Baz{
+										entries: map[int]interface{}{
+											-2:	&Foo{},
+											-5:	&Bar{},
+											-7:	&Baz{whatever: "are you serious?"}}}},
+										bang:	&Bar{foo: []*Foo{}}},
+									&Foo{bar: &Bar{baz: &Baz{
+										entries: map[int]interface{}{
+											-100:	&Foo{},
+											50:	&Bar{},
+											20:	&Baz{whatever: "na, not really ..."}}}},
+										bang:	&Bar{foo: []*Foo{}}}}}}}}},
+					&Foo{bar: &Bar{baz: &Baz{
+						entries: map[int]interface{}{
+							2:	&Foo{},
+							1:	&Bar{},
+							-1:	&Baz{whatever: "... it's just a test."}}}},
+						bang:	&Bar{foo: []*Foo{}}}}}}}}}
+}
+
+func TestElaborate(t *testing.T) {
+	a := newFoo()
+	b := newFoo()
+
+	if err := deepequal.Check(a, b); err != nil {
+		t.Errorf("expected nil, saw %v", err)
+	}
+}
diff --git a/src/pkg/go/printer/testdata/slow.input b/src/pkg/go/printer/testdata/slow.input
new file mode 100644
index 000000000..0e5a23d88
--- /dev/null
+++ b/src/pkg/go/printer/testdata/slow.input
@@ -0,0 +1,85 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package deepequal_test
+
+import (
+        "testing"
+        "google3/spam/archer/frontend/deepequal"
+)
+
+func TestTwoNilValues(t *testing.T) {
+        if err := deepequal.Check(nil, nil); err != nil {
+                t.Errorf("expected nil, saw %v", err)
+        }
+}
+
+type Foo struct {
+        bar *Bar
+        bang *Bar
+}
+
+type Bar struct {
+        baz *Baz
+        foo []*Foo
+}
+
+type Baz struct {
+        entries  map[int]interface{}
+        whatever string
+}
+
+func newFoo() (*Foo) {
+return &Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+42: &Foo{},
+21: &Bar{},
+11: &Baz{ whatever: "it's just a test" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+43: &Foo{},
+22: &Bar{},
+13: &Baz{ whatever: "this is nuts" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+61: &Foo{},
+71: &Bar{},
+11: &Baz{ whatever: "no, it's Go" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+0: &Foo{},
+-2: &Bar{},
+-11: &Baz{ whatever: "we need to go deeper" }}}},
+        bang: &Bar{foo: []*Foo{
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+-2: &Foo{},
+-5: &Bar{},
+-7: &Baz{ whatever: "are you serious?" }}}},
+        bang: &Bar{foo: []*Foo{}}},
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+-100: &Foo{},
+50: &Bar{},
+20: &Baz{ whatever: "na, not really ..." }}}},
+        bang: &Bar{foo: []*Foo{}}}}}}}}},
+&Foo{bar: &Bar{ baz: &Baz{
+entries: map[int]interface{}{
+2: &Foo{},
+1: &Bar{},
+-1: &Baz{ whatever: "... it's just a test." }}}},
+        bang: &Bar{foo: []*Foo{}}}}}}}}}
+}
+
+func TestElaborate(t *testing.T) {
+        a := newFoo()
+        b := newFoo()
+
+        if err := deepequal.Check(a, b); err != nil {
+                t.Errorf("expected nil, saw %v", err)
+        }
+}
diff --git a/src/pkg/go/printer/testdata/statements.golden b/src/pkg/go/printer/testdata/statements.golden
new file mode 100644
index 000000000..a6d85107f
--- /dev/null
+++ b/src/pkg/go/printer/testdata/statements.golden
@@ -0,0 +1,412 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package statements
+
+var expr bool
+
+func use(x interface{})	{}
+
+// Formatting of if-statement headers.
+func _() {
+	if true {
+	}
+	if true {
+	}	// no semicolon printed
+	if expr {
+	}
+	if expr {
+	}	// no semicolon printed
+	if expr {
+	}	// no parens printed
+	if expr {
+	}	// no semicolon and parens printed
+	if x := expr; true {
+		use(x)
+	}
+	if x := expr; expr {
+		use(x)
+	}
+}
+
+// Formatting of switch-statement headers.
+func _() {
+	switch {
+	}
+	switch {
+	}	// no semicolon printed
+	switch expr {
+	}
+	switch expr {
+	}	// no semicolon printed
+	switch expr {
+	}	// no parens printed
+	switch expr {
+	}	// no semicolon and parens printed
+	switch x := expr; {
+	default:
+		use(
+			x)
+	}
+	switch x := expr; expr {
+	default:
+		use(x)
+	}
+}
+
+// Formatting of switch statement bodies.
+func _() {
+	switch {
+	}
+
+	switch x := 0; x {
+	case 1:
+		use(x)
+		use(x)	// followed by an empty line
+
+	case 2:	// followed by an empty line
+
+		use(x)	// followed by an empty line
+
+	case 3:	// no empty lines
+		use(x)
+		use(x)
+	}
+
+	switch x {
+	case 0:
+		use(x)
+	case 1:	// this comment should have no effect on the previous or next line
+		use(x)
+	}
+
+	switch x := 0; x {
+	case 1:
+		x = 0
+		// this comment should be indented
+	case 2:
+		x = 0
+	// this comment should not be indented, it is aligned with the next case
+	case 3:
+		x = 0
+		/* indented comment
+		   aligned
+		   aligned
+		*/
+		// bla
+		/* and more */
+	case 4:
+		x = 0
+	/* not indented comment
+	   aligned
+	   aligned
+	*/
+	// bla
+	/* and more */
+	case 5:
+	}
+}
+
+// Formatting of selected select statements.
+func _() {
+	select {}
+	select { /* this comment should not be tab-aligned because the closing } is on the same line */
+	}
+	select {	/* this comment should be tab-aligned */
+	}
+	select {	// this comment should be tab-aligned
+	}
+	select {
+	case <-c:
+	}
+}
+
+// Formatting of for-statement headers.
+func _() {
+	for {
+	}
+	for expr {
+	}
+	for expr {
+	}	// no parens printed
+	for {
+	}	// no semicolons printed
+	for x := expr; ; {
+		use(x)
+	}
+	for expr {
+	}	// no semicolons printed
+	for expr {
+	}	// no semicolons and parens printed
+	for ; ; expr = false {
+	}
+	for x := expr; expr; {
+		use(x)
+	}
+	for x := expr; ; expr = false {
+		use(x)
+	}
+	for ; expr; expr = false {
+	}
+	for x := expr; expr; expr = false {
+		use(x)
+	}
+	for x := range []int{} {
+		use(x)
+	}
+	for x := range []int{} {
+		use(x)
+	}	// no parens printed
+}
+
+// Don't remove mandatory parentheses around composite literals in control clauses.
+func _() {
+	// strip parentheses - no composite literals or composite literals don't start with a type name
+	if x {
+	}
+	if x {
+	}
+	if []T{} {
+	}
+	if []T{} {
+	}
+	if []T{} {
+	}
+
+	for x {
+	}
+	for x {
+	}
+	for []T{} {
+	}
+	for []T{} {
+	}
+	for []T{} {
+	}
+
+	switch x {
+	}
+	switch x {
+	}
+	switch []T{} {
+	}
+	switch []T{} {
+	}
+
+	for _ = range []T{T{42}} {
+	}
+
+	// leave parentheses - composite literals start with a type name
+	if (T{}) {
+	}
+	if (T{}) {
+	}
+	if (T{}) {
+	}
+
+	for (T{}) {
+	}
+	for (T{}) {
+	}
+	for (T{}) {
+	}
+
+	switch (T{}) {
+	}
+	switch (T{}) {
+	}
+
+	for _ = range (T1{T{42}}) {
+	}
+
+	if x == (T{42}[0]) {
+	}
+	if (x == T{42}[0]) {
+	}
+	if x == (T{42}[0]) {
+	}
+	if x == (T{42}[0]) {
+	}
+	if x == (T{42}[0]) {
+	}
+	if x == a+b*(T{42}[0]) {
+	}
+	if (x == a+b*T{42}[0]) {
+	}
+	if x == a+b*(T{42}[0]) {
+	}
+	if x == a+(b * (T{42}[0])) {
+	}
+	if x == a+b*(T{42}[0]) {
+	}
+	if (a + b*(T{42}[0])) == x {
+	}
+	if (a + b*(T{42}[0])) == x {
+	}
+
+	if struct{ x bool }{false}.x {
+	}
+	if (struct{ x bool }{false}.x) == false {
+	}
+	if struct{ x bool }{false}.x == false {
+	}
+}
+
+// Extra empty lines inside functions. Do respect source code line
+// breaks between statement boundaries but print at most one empty
+// line at a time.
+func _() {
+
+	const _ = 0
+
+	const _ = 1
+	type _ int
+	type _ float
+
+	var _ = 0
+	var x = 1
+
+	// Each use(x) call below should have at most one empty line before and after.
+	// Known bug: The first use call may have more than one empty line before
+	//            (see go/printer/nodes.go, func linebreak).
+
+
+	use(x)
+
+	if x < x {
+
+		use(x)
+
+	} else {
+
+		use(x)
+
+	}
+}
+
+// Formatting around labels.
+func _() {
+L:
+}
+
+func _() {
+	// this comment should be indented
+L:	// no semicolon needed
+}
+
+func _() {
+	switch 0 {
+	case 0:
+	L0:
+		;	// semicolon required
+	case 1:
+	L1:
+		;	// semicolon required
+	default:
+	L2:	// no semicolon needed
+	}
+}
+
+func _() {
+	f()
+L1:
+	f()
+L2:
+	;
+L3:
+}
+
+func _() {
+	// this comment should be indented
+L:
+}
+
+func _() {
+L:
+	_ = 0
+}
+
+func _() {
+	// this comment should be indented
+L:
+	_ = 0
+}
+
+func _() {
+	for {
+	L1:
+		_ = 0
+	L2:
+		_ = 0
+	}
+}
+
+func _() {
+	// this comment should be indented
+	for {
+	L1:
+		_ = 0
+	L2:
+		_ = 0
+	}
+}
+
+func _() {
+	if true {
+		_ = 0
+	}
+	_ = 0	// the indentation here should not be affected by the long label name
+AnOverlongLabel:
+	_ = 0
+
+	if true {
+		_ = 0
+	}
+	_ = 0
+
+L:
+	_ = 0
+}
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+	MoreCode()
+}
+
+func _() {
+	for {
+		goto L
+	}
+L:	// A comment on the same line as the label, followed by a single empty line.
+	// Known bug: There may be more than one empty line before MoreCode()
+	//            (see go/printer/nodes.go, func linebreak).
+
+
+	MoreCode()
+}
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}
+
+func _() {
+	for {
+		goto AVeryLongLabelThatShouldNotAffectFormatting
+	}
+AVeryLongLabelThatShouldNotAffectFormatting:
+	// There should be a single empty line after this comment.
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}
diff --git a/src/pkg/go/printer/testdata/statements.input b/src/pkg/go/printer/testdata/statements.input
new file mode 100644
index 000000000..86a753c5a
--- /dev/null
+++ b/src/pkg/go/printer/testdata/statements.input
@@ -0,0 +1,351 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package statements
+
+var expr bool
+
+func use(x interface{}) {}
+
+// Formatting of if-statement headers.
+func _() {
+	if true {}
+	if; true {}  // no semicolon printed
+	if expr{}
+	if;expr{}  // no semicolon printed
+	if (expr){}  // no parens printed
+	if;((expr)){}  // no semicolon and parens printed
+	if x:=expr;true{
+	use(x)}
+	if x:=expr; expr {use(x)}
+}
+
+
+// Formatting of switch-statement headers.
+func _() {
+	switch {}
+	switch;{}  // no semicolon printed
+	switch expr {}
+	switch;expr{}  // no semicolon printed
+	switch (expr) {}  // no parens printed
+	switch;((expr)){}  // no semicolon and parens printed
+	switch x := expr; { default:use(
+x)
+	}
+	switch x := expr; expr {default:use(x)}
+}
+
+
+// Formatting of switch statement bodies.
+func _() {
+	switch {
+	}
+
+	switch x := 0; x {
+	case 1:
+		use(x)
+		use(x)  // followed by an empty line
+
+	case 2:  // followed by an empty line
+
+		use(x)  // followed by an empty line
+
+	case 3:  // no empty lines
+		use(x)
+		use(x)
+	}
+
+	switch x {
+	case 0:
+		use(x)
+	case 1:  // this comment should have no effect on the previous or next line
+		use(x)
+	}
+
+	switch x := 0; x {
+	case 1:
+		x = 0
+		// this comment should be indented
+	case 2:
+		x = 0
+	// this comment should not be indented, it is aligned with the next case
+	case 3:
+		x = 0
+		/* indented comment
+		   aligned
+		   aligned
+		*/
+		// bla
+		/* and more */
+	case 4:
+		x = 0
+	/* not indented comment
+	   aligned
+	   aligned
+	*/
+	// bla
+	/* and more */
+	case 5:
+	}
+}
+
+
+// Formatting of selected select statements.
+func _() {
+	select {
+	}
+	select { /* this comment should not be tab-aligned because the closing } is on the same line */ }
+	select { /* this comment should be tab-aligned */
+	}
+	select { // this comment should be tab-aligned
+	}
+	select { case <-c: }
+}
+
+
+// Formatting of for-statement headers.
+func _() {
+	for{}
+	for expr {}
+	for (expr) {}  // no parens printed
+	for;;{}  // no semicolons printed
+	for x :=expr;; {use( x)}
+	for; expr;{}  // no semicolons printed
+	for; ((expr));{}  // no semicolons and parens printed
+	for; ; expr = false {}
+	for x :=expr; expr; {use(x)}
+	for x := expr;; expr=false {use(x)}
+	for;expr;expr =false {
+	}
+	for x := expr;expr;expr = false { use(x) }
+	for x := range []int{} { use(x) }
+	for x := range (([]int{})) { use(x) }  // no parens printed
+}
+
+
+// Don't remove mandatory parentheses around composite literals in control clauses.
+func _() {
+	// strip parentheses - no composite literals or composite literals don't start with a type name
+	if (x) {}
+	if (((x))) {}
+	if ([]T{}) {}
+	if (([]T{})) {}
+	if ; (((([]T{})))) {}
+
+	for (x) {}
+	for (((x))) {}
+	for ([]T{}) {}
+	for (([]T{})) {}
+	for ; (((([]T{})))) ; {}
+
+	switch (x) {}
+	switch (((x))) {}
+	switch ([]T{}) {}
+	switch ; (((([]T{})))) {}
+
+	for _ = range ((([]T{T{42}}))) {}
+
+	// leave parentheses - composite literals start with a type name
+	if (T{}) {}
+	if ((T{})) {}
+	if ; ((((T{})))) {}
+
+	for (T{}) {}
+	for ((T{})) {}
+	for ; ((((T{})))) ; {}
+
+	switch (T{}) {}
+	switch ; ((((T{})))) {}
+
+	for _ = range (((T1{T{42}}))) {}
+
+	if x == (T{42}[0]) {}
+	if (x == T{42}[0]) {}
+	if (x == (T{42}[0])) {}
+	if (x == (((T{42}[0])))) {}
+	if (((x == (T{42}[0])))) {}
+	if x == a + b*(T{42}[0]) {}
+	if (x == a + b*T{42}[0]) {}
+	if (x == a + b*(T{42}[0])) {}
+	if (x == a + ((b * (T{42}[0])))) {}
+	if (((x == a + b * (T{42}[0])))) {}
+	if (((a + b * (T{42}[0])) == x)) {}
+	if (((a + b * (T{42}[0])))) == x {}
+
+	if (struct{x bool}{false}.x) {}
+	if (struct{x bool}{false}.x) == false {}
+	if (struct{x bool}{false}.x == false) {}
+}
+
+
+// Extra empty lines inside functions. Do respect source code line
+// breaks between statement boundaries but print at most one empty
+// line at a time.
+func _() {
+
+	const _ = 0
+
+	const _ = 1
+	type _ int
+	type _ float
+
+	var _ = 0
+	var x = 1
+
+	// Each use(x) call below should have at most one empty line before and after.
+	// Known bug: The first use call may have more than one empty line before
+	//            (see go/printer/nodes.go, func linebreak).
+
+
+
+	use(x)
+
+	if x < x {
+
+		use(x)
+
+	} else {
+
+		use(x)
+
+	}
+}
+
+
+// Formatting around labels.
+func _() {
+	L:
+}
+
+
+func _() {
+	// this comment should be indented
+	L: ;  // no semicolon needed
+}
+
+
+func _() {
+	switch 0 {
+	case 0:
+		L0: ;  // semicolon required
+	case 1:
+		L1: ;  // semicolon required
+	default:
+		L2: ;  // no semicolon needed
+	}
+}
+
+
+func _() {
+	f()
+L1:
+	f()
+L2:
+	;
+L3:
+}
+
+
+func _() {
+	// this comment should be indented
+	L:
+}
+
+
+func _() {
+	L: _ = 0
+}
+
+
+func _() {
+	// this comment should be indented
+	L: _ = 0
+}
+
+
+func _() {
+	for {
+	L1: _ = 0
+	L2:
+		_ = 0
+	}
+}
+
+
+func _() {
+		// this comment should be indented
+	for {
+	L1: _ = 0
+	L2:
+		_ = 0
+	}
+}
+
+
+func _() {
+	if true {
+		_ = 0
+	}
+	_ = 0  // the indentation here should not be affected by the long label name
+AnOverlongLabel:
+	_ = 0
+	
+	if true {
+		_ = 0
+	}
+	_ = 0
+
+L:	_ = 0
+}
+
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto L
+	}
+L:	// A comment on the same line as the label, followed by a single empty line.
+	// Known bug: There may be more than one empty line before MoreCode()
+	//            (see go/printer/nodes.go, func linebreak).
+
+
+
+
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto L
+	}
+L:
+
+
+
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}
+
+
+func _() {
+	for {
+		goto AVeryLongLabelThatShouldNotAffectFormatting
+	}
+AVeryLongLabelThatShouldNotAffectFormatting:
+	// There should be a single empty line after this comment.
+
+	// There should be a single empty line before this comment.
+	MoreCode()
+}
diff --git a/src/pkg/go/scanner/Makefile b/src/pkg/go/scanner/Makefile
new file mode 100644
index 000000000..453faac00
--- /dev/null
+++ b/src/pkg/go/scanner/Makefile
@@ -0,0 +1,12 @@
+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../Make.inc
+
+TARG=go/scanner
+GOFILES=\
+	errors.go\
+	scanner.go\
+
+include ../../../Make.pkg
diff --git a/src/pkg/go/scanner/errors.go b/src/pkg/go/scanner/errors.go
new file mode 100644
index 000000000..a0927e416
--- /dev/null
+++ b/src/pkg/go/scanner/errors.go
@@ -0,0 +1,168 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package scanner
+
+import (
+	"fmt"
+	"go/token"
+	"io"
+	"os"
+	"sort"
+)
+
+// An implementation of an ErrorHandler may be provided to the Scanner.
+// If a syntax error is encountered and a handler was installed, Error
+// is called with a position and an error message. The position points
+// to the beginning of the offending token.
+//
+type ErrorHandler interface {
+	Error(pos token.Position, msg string)
+}
+
+// ErrorVector implements the ErrorHandler interface. It maintains a list
+// of errors which can be retrieved with GetErrorList and GetError. The
+// zero value for an ErrorVector is an empty ErrorVector ready to use.
+//
+// A common usage pattern is to embed an ErrorVector alongside a
+// scanner in a data structure that uses the scanner. By passing a
+// reference to an ErrorVector to the scanner's Init call, default
+// error handling is obtained.
+//
+type ErrorVector struct {
+	errors []*Error
+}
+
+// Reset resets an ErrorVector to no errors.
+func (h *ErrorVector) Reset() { h.errors = h.errors[:0] }
+
+// ErrorCount returns the number of errors collected.
+func (h *ErrorVector) ErrorCount() int { return len(h.errors) }
+
+// Within ErrorVector, an error is represented by an Error node. The
+// position Pos, if valid, points to the beginning of the offending
+// token, and the error condition is described by Msg.
+//
+type Error struct {
+	Pos token.Position
+	Msg string
+}
+
+func (e *Error) String() string {
+	if e.Pos.Filename != "" || e.Pos.IsValid() {
+		// don't print "<unknown position>"
+		// TODO(gri) reconsider the semantics of Position.IsValid
+		return e.Pos.String() + ": " + e.Msg
+	}
+	return e.Msg
+}
+
+// An ErrorList is a (possibly sorted) list of Errors.
+type ErrorList []*Error
+
+// ErrorList implements the sort Interface.
+func (p ErrorList) Len() int      { return len(p) }
+func (p ErrorList) Swap(i, j int) { p[i], p[j] = p[j], p[i] }
+
+func (p ErrorList) Less(i, j int) bool {
+	e := &p[i].Pos
+	f := &p[j].Pos
+	// Note that it is not sufficient to simply compare file offsets because
+	// the offsets do not reflect modified line information (through //line
+	// comments).
+	if e.Filename < f.Filename {
+		return true
+	}
+	if e.Filename == f.Filename {
+		if e.Line < f.Line {
+			return true
+		}
+		if e.Line == f.Line {
+			return e.Column < f.Column
+		}
+	}
+	return false
+}
+
+func (p ErrorList) String() string {
+	switch len(p) {
+	case 0:
+		return "unspecified error"
+	case 1:
+		return p[0].String()
+	}
+	return fmt.Sprintf("%s (and %d more errors)", p[0].String(), len(p)-1)
+}
+
+// These constants control the construction of the ErrorList
+// returned by GetErrors.
+//
+const (
+	Raw         = iota // leave error list unchanged
+	Sorted             // sort error list by file, line, and column number
+	NoMultiples        // sort error list and leave only the first error per line
+)
+
+// GetErrorList returns the list of errors collected by an ErrorVector.
+// The construction of the ErrorList returned is controlled by the mode
+// parameter. If there are no errors, the result is nil.
+//
+func (h *ErrorVector) GetErrorList(mode int) ErrorList {
+	if len(h.errors) == 0 {
+		return nil
+	}
+
+	list := make(ErrorList, len(h.errors))
+	copy(list, h.errors)
+
+	if mode >= Sorted {
+		sort.Sort(list)
+	}
+
+	if mode >= NoMultiples {
+		var last token.Position // initial last.Line is != any legal error line
+		i := 0
+		for _, e := range list {
+			if e.Pos.Filename != last.Filename || e.Pos.Line != last.Line {
+				last = e.Pos
+				list[i] = e
+				i++
+			}
+		}
+		list = list[0:i]
+	}
+
+	return list
+}
+
+// GetError is like GetErrorList, but it returns an os.Error instead
+// so that a nil result can be assigned to an os.Error variable and
+// remains nil.
+//
+func (h *ErrorVector) GetError(mode int) os.Error {
+	if len(h.errors) == 0 {
+		return nil
+	}
+
+	return h.GetErrorList(mode)
+}
+
+// ErrorVector implements the ErrorHandler interface.
+func (h *ErrorVector) Error(pos token.Position, msg string) {
+	h.errors = append(h.errors, &Error{pos, msg})
+}
+
+// PrintError is a utility function that prints a list of errors to w,
+// one error per line, if the err parameter is an ErrorList. Otherwise
+// it prints the err string.
+//
+func PrintError(w io.Writer, err os.Error) {
+	if list, ok := err.(ErrorList); ok {
+		for _, e := range list {
+			fmt.Fprintf(w, "%s\n", e)
+		}
+	} else {
+		fmt.Fprintf(w, "%s\n", err)
+	}
+}
diff --git a/src/pkg/go/scanner/scanner.go b/src/pkg/go/scanner/scanner.go
new file mode 100644
index 000000000..7f3dd2373
--- /dev/null
+++ b/src/pkg/go/scanner/scanner.go
@@ -0,0 +1,670 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package scanner implements a scanner for Go source text. Takes a []byte as
+// source which can then be tokenized through repeated calls to the Scan
+// function. Typical use:
+//
+//	var s Scanner
+//	fset := token.NewFileSet()  // position information is relative to fset
+//      file := fset.AddFile(filename, fset.Base(), len(src))  // register file
+//	s.Init(file, src, nil /* no error handler */, 0)
+//	for {
+//		pos, tok, lit := s.Scan()
+//		if tok == token.EOF {
+//			break
+//		}
+//		// do something here with pos, tok, and lit
+//	}
+//
+package scanner
+
+import (
+	"bytes"
+	"fmt"
+	"go/token"
+	"path/filepath"
+	"strconv"
+	"unicode"
+	"utf8"
+)
+
+// A Scanner holds the scanner's internal state while processing
+// a given text.  It can be allocated as part of another data
+// structure but must be initialized via Init before use.
+//
+type Scanner struct {
+	// immutable state
+	file *token.File  // source file handle
+	dir  string       // directory portion of file.Name()
+	src  []byte       // source
+	err  ErrorHandler // error reporting; or nil
+	mode uint         // scanning mode
+
+	// scanning state
+	ch         int  // current character
+	offset     int  // character offset
+	rdOffset   int  // reading offset (position after current character)
+	lineOffset int  // current line offset
+	insertSemi bool // insert a semicolon before next newline
+
+	// public state - ok to modify
+	ErrorCount int // number of errors encountered
+}
+
+// Read the next Unicode char into S.ch.
+// S.ch < 0 means end-of-file.
+//
+func (S *Scanner) next() {
+	if S.rdOffset < len(S.src) {
+		S.offset = S.rdOffset
+		if S.ch == '\n' {
+			S.lineOffset = S.offset
+			S.file.AddLine(S.offset)
+		}
+		r, w := int(S.src[S.rdOffset]), 1
+		switch {
+		case r == 0:
+			S.error(S.offset, "illegal character NUL")
+		case r >= 0x80:
+			// not ASCII
+			r, w = utf8.DecodeRune(S.src[S.rdOffset:])
+			if r == utf8.RuneError && w == 1 {
+				S.error(S.offset, "illegal UTF-8 encoding")
+			}
+		}
+		S.rdOffset += w
+		S.ch = r
+	} else {
+		S.offset = len(S.src)
+		if S.ch == '\n' {
+			S.lineOffset = S.offset
+			S.file.AddLine(S.offset)
+		}
+		S.ch = -1 // eof
+	}
+}
+
+// The mode parameter to the Init function is a set of flags (or 0).
+// They control scanner behavior.
+//
+const (
+	ScanComments      = 1 << iota // return comments as COMMENT tokens
+	AllowIllegalChars             // do not report an error for illegal chars
+	InsertSemis                   // automatically insert semicolons
+)
+
+// Init prepares the scanner S to tokenize the text src by setting the
+// scanner at the beginning of src. The scanner uses the file set file
+// for position information and it adds line information for each line.
+// It is ok to re-use the same file when re-scanning the same file as
+// line information which is already present is ignored. Init causes a
+// panic if the file size does not match the src size.
+//
+// Calls to Scan will use the error handler err if they encounter a
+// syntax error and err is not nil. Also, for each error encountered,
+// the Scanner field ErrorCount is incremented by one. The mode parameter
+// determines how comments, illegal characters, and semicolons are handled.
+//
+// Note that Init may call err if there is an error in the first character
+// of the file.
+//
+func (S *Scanner) Init(file *token.File, src []byte, err ErrorHandler, mode uint) {
+	// Explicitly initialize all fields since a scanner may be reused.
+	if file.Size() != len(src) {
+		panic("file size does not match src len")
+	}
+	S.file = file
+	S.dir, _ = filepath.Split(file.Name())
+	S.src = src
+	S.err = err
+	S.mode = mode
+
+	S.ch = ' '
+	S.offset = 0
+	S.rdOffset = 0
+	S.lineOffset = 0
+	S.insertSemi = false
+	S.ErrorCount = 0
+
+	S.next()
+}
+
+func (S *Scanner) error(offs int, msg string) {
+	if S.err != nil {
+		S.err.Error(S.file.Position(S.file.Pos(offs)), msg)
+	}
+	S.ErrorCount++
+}
+
+var prefix = []byte("//line ")
+
+func (S *Scanner) interpretLineComment(text []byte) {
+	if bytes.HasPrefix(text, prefix) {
+		// get filename and line number, if any
+		if i := bytes.LastIndex(text, []byte{':'}); i > 0 {
+			if line, err := strconv.Atoi(string(text[i+1:])); err == nil && line > 0 {
+				// valid //line filename:line comment;
+				filename := filepath.Clean(string(text[len(prefix):i]))
+				if !filepath.IsAbs(filename) {
+					// make filename relative to current directory
+					filename = filepath.Join(S.dir, filename)
+				}
+				// update scanner position
+				S.file.AddLineInfo(S.lineOffset, filename, line-1) // -1 since comment applies to next line
+			}
+		}
+	}
+}
+
+func (S *Scanner) scanComment() {
+	// initial '/' already consumed; S.ch == '/' || S.ch == '*'
+	offs := S.offset - 1 // position of initial '/'
+
+	if S.ch == '/' {
+		//-style comment
+		S.next()
+		for S.ch != '\n' && S.ch >= 0 {
+			S.next()
+		}
+		if offs == S.lineOffset {
+			// comment starts at the beginning of the current line
+			S.interpretLineComment(S.src[offs:S.offset])
+		}
+		return
+	}
+
+	/*-style comment */
+	S.next()
+	for S.ch >= 0 {
+		ch := S.ch
+		S.next()
+		if ch == '*' && S.ch == '/' {
+			S.next()
+			return
+		}
+	}
+
+	S.error(offs, "comment not terminated")
+}
+
+func (S *Scanner) findLineEnd() bool {
+	// initial '/' already consumed
+
+	defer func(offs int) {
+		// reset scanner state to where it was upon calling findLineEnd
+		S.ch = '/'
+		S.offset = offs
+		S.rdOffset = offs + 1
+		S.next() // consume initial '/' again
+	}(S.offset - 1)
+
+	// read ahead until a newline, EOF, or non-comment token is found
+	for S.ch == '/' || S.ch == '*' {
+		if S.ch == '/' {
+			//-style comment always contains a newline
+			return true
+		}
+		/*-style comment: look for newline */
+		S.next()
+		for S.ch >= 0 {
+			ch := S.ch
+			if ch == '\n' {
+				return true
+			}
+			S.next()
+			if ch == '*' && S.ch == '/' {
+				S.next()
+				break
+			}
+		}
+		S.skipWhitespace() // S.insertSemi is set
+		if S.ch < 0 || S.ch == '\n' {
+			return true
+		}
+		if S.ch != '/' {
+			// non-comment token
+			return false
+		}
+		S.next() // consume '/'
+	}
+
+	return false
+}
+
+func isLetter(ch int) bool {
+	return 'a' <= ch && ch <= 'z' || 'A' <= ch && ch <= 'Z' || ch == '_' || ch >= 0x80 && unicode.IsLetter(ch)
+}
+
+func isDigit(ch int) bool {
+	return '0' <= ch && ch <= '9' || ch >= 0x80 && unicode.IsDigit(ch)
+}
+
+func (S *Scanner) scanIdentifier() token.Token {
+	offs := S.offset
+	for isLetter(S.ch) || isDigit(S.ch) {
+		S.next()
+	}
+	return token.Lookup(S.src[offs:S.offset])
+}
+
+func digitVal(ch int) int {
+	switch {
+	case '0' <= ch && ch <= '9':
+		return ch - '0'
+	case 'a' <= ch && ch <= 'f':
+		return ch - 'a' + 10
+	case 'A' <= ch && ch <= 'F':
+		return ch - 'A' + 10
+	}
+	return 16 // larger than any legal digit val
+}
+
+func (S *Scanner) scanMantissa(base int) {
+	for digitVal(S.ch) < base {
+		S.next()
+	}
+}
+
+func (S *Scanner) scanNumber(seenDecimalPoint bool) token.Token {
+	// digitVal(S.ch) < 10
+	tok := token.INT
+
+	if seenDecimalPoint {
+		tok = token.FLOAT
+		S.scanMantissa(10)
+		goto exponent
+	}
+
+	if S.ch == '0' {
+		// int or float
+		offs := S.offset
+		S.next()
+		if S.ch == 'x' || S.ch == 'X' {
+			// hexadecimal int
+			S.next()
+			S.scanMantissa(16)
+			if S.offset-offs <= 2 {
+				// only scanned "0x" or "0X"
+				S.error(offs, "illegal hexadecimal number")
+			}
+		} else {
+			// octal int or float
+			seenDecimalDigit := false
+			S.scanMantissa(8)
+			if S.ch == '8' || S.ch == '9' {
+				// illegal octal int or float
+				seenDecimalDigit = true
+				S.scanMantissa(10)
+			}
+			if S.ch == '.' || S.ch == 'e' || S.ch == 'E' || S.ch == 'i' {
+				goto fraction
+			}
+			// octal int
+			if seenDecimalDigit {
+				S.error(offs, "illegal octal number")
+			}
+		}
+		goto exit
+	}
+
+	// decimal int or float
+	S.scanMantissa(10)
+
+fraction:
+	if S.ch == '.' {
+		tok = token.FLOAT
+		S.next()
+		S.scanMantissa(10)
+	}
+
+exponent:
+	if S.ch == 'e' || S.ch == 'E' {
+		tok = token.FLOAT
+		S.next()
+		if S.ch == '-' || S.ch == '+' {
+			S.next()
+		}
+		S.scanMantissa(10)
+	}
+
+	if S.ch == 'i' {
+		tok = token.IMAG
+		S.next()
+	}
+
+exit:
+	return tok
+}
+
+func (S *Scanner) scanEscape(quote int) {
+	offs := S.offset
+
+	var i, base, max uint32
+	switch S.ch {
+	case 'a', 'b', 'f', 'n', 'r', 't', 'v', '\\', quote:
+		S.next()
+		return
+	case '0', '1', '2', '3', '4', '5', '6', '7':
+		i, base, max = 3, 8, 255
+	case 'x':
+		S.next()
+		i, base, max = 2, 16, 255
+	case 'u':
+		S.next()
+		i, base, max = 4, 16, unicode.MaxRune
+	case 'U':
+		S.next()
+		i, base, max = 8, 16, unicode.MaxRune
+	default:
+		S.next() // always make progress
+		S.error(offs, "unknown escape sequence")
+		return
+	}
+
+	var x uint32
+	for ; i > 0 && S.ch != quote && S.ch >= 0; i-- {
+		d := uint32(digitVal(S.ch))
+		if d >= base {
+			S.error(S.offset, "illegal character in escape sequence")
+			break
+		}
+		x = x*base + d
+		S.next()
+	}
+	// in case of an error, consume remaining chars
+	for ; i > 0 && S.ch != quote && S.ch >= 0; i-- {
+		S.next()
+	}
+	if x > max || 0xd800 <= x && x < 0xe000 {
+		S.error(offs, "escape sequence is invalid Unicode code point")
+	}
+}
+
+func (S *Scanner) scanChar() {
+	// '\'' opening already consumed
+	offs := S.offset - 1
+
+	n := 0
+	for S.ch != '\'' {
+		ch := S.ch
+		n++
+		S.next()
+		if ch == '\n' || ch < 0 {
+			S.error(offs, "character literal not terminated")
+			n = 1
+			break
+		}
+		if ch == '\\' {
+			S.scanEscape('\'')
+		}
+	}
+
+	S.next()
+
+	if n != 1 {
+		S.error(offs, "illegal character literal")
+	}
+}
+
+func (S *Scanner) scanString() {
+	// '"' opening already consumed
+	offs := S.offset - 1
+
+	for S.ch != '"' {
+		ch := S.ch
+		S.next()
+		if ch == '\n' || ch < 0 {
+			S.error(offs, "string not terminated")
+			break
+		}
+		if ch == '\\' {
+			S.scanEscape('"')
+		}
+	}
+
+	S.next()
+}
+
+func (S *Scanner) scanRawString() {
+	// '`' opening already consumed
+	offs := S.offset - 1
+
+	for S.ch != '`' {
+		ch := S.ch
+		S.next()
+		if ch < 0 {
+			S.error(offs, "string not terminated")
+			break
+		}
+	}
+
+	S.next()
+}
+
+func (S *Scanner) skipWhitespace() {
+	for S.ch == ' ' || S.ch == '\t' || S.ch == '\n' && !S.insertSemi || S.ch == '\r' {
+		S.next()
+	}
+}
+
+// Helper functions for scanning multi-byte tokens such as >> += >>= .
+// Different routines recognize different length tok_i based on matches
+// of ch_i. If a token ends in '=', the result is tok1 or tok3
+// respectively. Otherwise, the result is tok0 if there was no other
+// matching character, or tok2 if the matching character was ch2.
+
+func (S *Scanner) switch2(tok0, tok1 token.Token) token.Token {
+	if S.ch == '=' {
+		S.next()
+		return tok1
+	}
+	return tok0
+}
+
+func (S *Scanner) switch3(tok0, tok1 token.Token, ch2 int, tok2 token.Token) token.Token {
+	if S.ch == '=' {
+		S.next()
+		return tok1
+	}
+	if S.ch == ch2 {
+		S.next()
+		return tok2
+	}
+	return tok0
+}
+
+func (S *Scanner) switch4(tok0, tok1 token.Token, ch2 int, tok2, tok3 token.Token) token.Token {
+	if S.ch == '=' {
+		S.next()
+		return tok1
+	}
+	if S.ch == ch2 {
+		S.next()
+		if S.ch == '=' {
+			S.next()
+			return tok3
+		}
+		return tok2
+	}
+	return tok0
+}
+
+// Scan scans the next token and returns the token position,
+// the token, and the literal string corresponding to the
+// token. The source end is indicated by token.EOF.
+//
+// If the returned token is token.SEMICOLON, the corresponding
+// literal string is ";" if the semicolon was present in the source,
+// and "\n" if the semicolon was inserted because of a newline or
+// at EOF.
+//
+// For more tolerant parsing, Scan will return a valid token if
+// possible even if a syntax error was encountered. Thus, even
+// if the resulting token sequence contains no illegal tokens,
+// a client may not assume that no error occurred. Instead it
+// must check the scanner's ErrorCount or the number of calls
+// of the error handler, if there was one installed.
+//
+// Scan adds line information to the file added to the file
+// set with Init. Token positions are relative to that file
+// and thus relative to the file set.
+//
+func (S *Scanner) Scan() (token.Pos, token.Token, string) {
+scanAgain:
+	S.skipWhitespace()
+
+	// current token start
+	insertSemi := false
+	offs := S.offset
+	tok := token.ILLEGAL
+
+	// determine token value
+	switch ch := S.ch; {
+	case isLetter(ch):
+		tok = S.scanIdentifier()
+		switch tok {
+		case token.IDENT, token.BREAK, token.CONTINUE, token.FALLTHROUGH, token.RETURN:
+			insertSemi = true
+		}
+	case digitVal(ch) < 10:
+		insertSemi = true
+		tok = S.scanNumber(false)
+	default:
+		S.next() // always make progress
+		switch ch {
+		case -1:
+			if S.insertSemi {
+				S.insertSemi = false // EOF consumed
+				return S.file.Pos(offs), token.SEMICOLON, "\n"
+			}
+			tok = token.EOF
+		case '\n':
+			// we only reach here if S.insertSemi was
+			// set in the first place and exited early
+			// from S.skipWhitespace()
+			S.insertSemi = false // newline consumed
+			return S.file.Pos(offs), token.SEMICOLON, "\n"
+		case '"':
+			insertSemi = true
+			tok = token.STRING
+			S.scanString()
+		case '\'':
+			insertSemi = true
+			tok = token.CHAR
+			S.scanChar()
+		case '`':
+			insertSemi = true
+			tok = token.STRING
+			S.scanRawString()
+		case ':':
+			tok = S.switch2(token.COLON, token.DEFINE)
+		case '.':
+			if digitVal(S.ch) < 10 {
+				insertSemi = true
+				tok = S.scanNumber(true)
+			} else if S.ch == '.' {
+				S.next()
+				if S.ch == '.' {
+					S.next()
+					tok = token.ELLIPSIS
+				}
+			} else {
+				tok = token.PERIOD
+			}
+		case ',':
+			tok = token.COMMA
+		case ';':
+			tok = token.SEMICOLON
+		case '(':
+			tok = token.LPAREN
+		case ')':
+			insertSemi = true
+			tok = token.RPAREN
+		case '[':
+			tok = token.LBRACK
+		case ']':
+			insertSemi = true
+			tok = token.RBRACK
+		case '{':
+			tok = token.LBRACE
+		case '}':
+			insertSemi = true
+			tok = token.RBRACE
+		case '+':
+			tok = S.switch3(token.ADD, token.ADD_ASSIGN, '+', token.INC)
+			if tok == token.INC {
+				insertSemi = true
+			}
+		case '-':
+			tok = S.switch3(token.SUB, token.SUB_ASSIGN, '-', token.DEC)
+			if tok == token.DEC {
+				insertSemi = true
+			}
+		case '*':
+			tok = S.switch2(token.MUL, token.MUL_ASSIGN)
+		case '/':
+			if S.ch == '/' || S.ch == '*' {
+				// comment
+				if S.insertSemi && S.findLineEnd() {
+					// reset position to the beginning of the comment
+					S.ch = '/'
+					S.offset = offs
+					S.rdOffset = offs + 1
+					S.insertSemi = false // newline consumed
+					return S.file.Pos(offs), token.SEMICOLON, "\n"
+				}
+				S.scanComment()
+				if S.mode&ScanComments == 0 {
+					// skip comment
+					S.insertSemi = false // newline consumed
+					goto scanAgain
+				}
+				tok = token.COMMENT
+			} else {
+				tok = S.switch2(token.QUO, token.QUO_ASSIGN)
+			}
+		case '%':
+			tok = S.switch2(token.REM, token.REM_ASSIGN)
+		case '^':
+			tok = S.switch2(token.XOR, token.XOR_ASSIGN)
+		case '<':
+			if S.ch == '-' {
+				S.next()
+				tok = token.ARROW
+			} else {
+				tok = S.switch4(token.LSS, token.LEQ, '<', token.SHL, token.SHL_ASSIGN)
+			}
+		case '>':
+			tok = S.switch4(token.GTR, token.GEQ, '>', token.SHR, token.SHR_ASSIGN)
+		case '=':
+			tok = S.switch2(token.ASSIGN, token.EQL)
+		case '!':
+			tok = S.switch2(token.NOT, token.NEQ)
+		case '&':
+			if S.ch == '^' {
+				S.next()
+				tok = S.switch2(token.AND_NOT, token.AND_NOT_ASSIGN)
+			} else {
+				tok = S.switch3(token.AND, token.AND_ASSIGN, '&', token.LAND)
+			}
+		case '|':
+			tok = S.switch3(token.OR, token.OR_ASSIGN, '|', token.LOR)
+		default:
+			if S.mode&AllowIllegalChars == 0 {
+				S.error(offs, fmt.Sprintf("illegal character %#U", ch))
+			}
+			insertSemi = S.insertSemi // preserve insertSemi info
+		}
+	}
+
+	if S.mode&InsertSemis != 0 {
+		S.insertSemi = insertSemi
+	}
+
+	// TODO(gri): The scanner API should change such that the literal string
+	//            is only valid if an actual literal was scanned. This will
+	//            permit a more efficient implementation.
+	return S.file.Pos(offs), tok, string(S.src[offs:S.offset])
+}
diff --git a/src/pkg/go/scanner/scanner_test.go b/src/pkg/go/scanner/scanner_test.go
new file mode 100644
index 000000000..eb9e1cb81
--- /dev/null
+++ b/src/pkg/go/scanner/scanner_test.go
@@ -0,0 +1,672 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package scanner
+
+import (
+	"go/token"
+	"os"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+var fset = token.NewFileSet()
+
+const /* class */ (
+	special = iota
+	literal
+	operator
+	keyword
+)
+
+func tokenclass(tok token.Token) int {
+	switch {
+	case tok.IsLiteral():
+		return literal
+	case tok.IsOperator():
+		return operator
+	case tok.IsKeyword():
+		return keyword
+	}
+	return special
+}
+
+type elt struct {
+	tok   token.Token
+	lit   string
+	class int
+}
+
+var tokens = [...]elt{
+	// Special tokens
+	{token.COMMENT, "/* a comment */", special},
+	{token.COMMENT, "// a comment \n", special},
+
+	// Identifiers and basic type literals
+	{token.IDENT, "foobar", literal},
+	{token.IDENT, "a۰۱۸", literal},
+	{token.IDENT, "foo६४", literal},
+	{token.IDENT, "bar９８７６", literal},
+	{token.INT, "0", literal},
+	{token.INT, "1", literal},
+	{token.INT, "123456789012345678890", literal},
+	{token.INT, "01234567", literal},
+	{token.INT, "0xcafebabe", literal},
+	{token.FLOAT, "0.", literal},
+	{token.FLOAT, ".0", literal},
+	{token.FLOAT, "3.14159265", literal},
+	{token.FLOAT, "1e0", literal},
+	{token.FLOAT, "1e+100", literal},
+	{token.FLOAT, "1e-100", literal},
+	{token.FLOAT, "2.71828e-1000", literal},
+	{token.IMAG, "0i", literal},
+	{token.IMAG, "1i", literal},
+	{token.IMAG, "012345678901234567889i", literal},
+	{token.IMAG, "123456789012345678890i", literal},
+	{token.IMAG, "0.i", literal},
+	{token.IMAG, ".0i", literal},
+	{token.IMAG, "3.14159265i", literal},
+	{token.IMAG, "1e0i", literal},
+	{token.IMAG, "1e+100i", literal},
+	{token.IMAG, "1e-100i", literal},
+	{token.IMAG, "2.71828e-1000i", literal},
+	{token.CHAR, "'a'", literal},
+	{token.CHAR, "'\\000'", literal},
+	{token.CHAR, "'\\xFF'", literal},
+	{token.CHAR, "'\\uff16'", literal},
+	{token.CHAR, "'\\U0000ff16'", literal},
+	{token.STRING, "`foobar`", literal},
+	{token.STRING, "`" + `foo
+	                        bar` +
+		"`",
+		literal,
+	},
+
+	// Operators and delimiters
+	{token.ADD, "+", operator},
+	{token.SUB, "-", operator},
+	{token.MUL, "*", operator},
+	{token.QUO, "/", operator},
+	{token.REM, "%", operator},
+
+	{token.AND, "&", operator},
+	{token.OR, "|", operator},
+	{token.XOR, "^", operator},
+	{token.SHL, "<<", operator},
+	{token.SHR, ">>", operator},
+	{token.AND_NOT, "&^", operator},
+
+	{token.ADD_ASSIGN, "+=", operator},
+	{token.SUB_ASSIGN, "-=", operator},
+	{token.MUL_ASSIGN, "*=", operator},
+	{token.QUO_ASSIGN, "/=", operator},
+	{token.REM_ASSIGN, "%=", operator},
+
+	{token.AND_ASSIGN, "&=", operator},
+	{token.OR_ASSIGN, "|=", operator},
+	{token.XOR_ASSIGN, "^=", operator},
+	{token.SHL_ASSIGN, "<<=", operator},
+	{token.SHR_ASSIGN, ">>=", operator},
+	{token.AND_NOT_ASSIGN, "&^=", operator},
+
+	{token.LAND, "&&", operator},
+	{token.LOR, "||", operator},
+	{token.ARROW, "<-", operator},
+	{token.INC, "++", operator},
+	{token.DEC, "--", operator},
+
+	{token.EQL, "==", operator},
+	{token.LSS, "<", operator},
+	{token.GTR, ">", operator},
+	{token.ASSIGN, "=", operator},
+	{token.NOT, "!", operator},
+
+	{token.NEQ, "!=", operator},
+	{token.LEQ, "<=", operator},
+	{token.GEQ, ">=", operator},
+	{token.DEFINE, ":=", operator},
+	{token.ELLIPSIS, "...", operator},
+
+	{token.LPAREN, "(", operator},
+	{token.LBRACK, "[", operator},
+	{token.LBRACE, "{", operator},
+	{token.COMMA, ",", operator},
+	{token.PERIOD, ".", operator},
+
+	{token.RPAREN, ")", operator},
+	{token.RBRACK, "]", operator},
+	{token.RBRACE, "}", operator},
+	{token.SEMICOLON, ";", operator},
+	{token.COLON, ":", operator},
+
+	// Keywords
+	{token.BREAK, "break", keyword},
+	{token.CASE, "case", keyword},
+	{token.CHAN, "chan", keyword},
+	{token.CONST, "const", keyword},
+	{token.CONTINUE, "continue", keyword},
+
+	{token.DEFAULT, "default", keyword},
+	{token.DEFER, "defer", keyword},
+	{token.ELSE, "else", keyword},
+	{token.FALLTHROUGH, "fallthrough", keyword},
+	{token.FOR, "for", keyword},
+
+	{token.FUNC, "func", keyword},
+	{token.GO, "go", keyword},
+	{token.GOTO, "goto", keyword},
+	{token.IF, "if", keyword},
+	{token.IMPORT, "import", keyword},
+
+	{token.INTERFACE, "interface", keyword},
+	{token.MAP, "map", keyword},
+	{token.PACKAGE, "package", keyword},
+	{token.RANGE, "range", keyword},
+	{token.RETURN, "return", keyword},
+
+	{token.SELECT, "select", keyword},
+	{token.STRUCT, "struct", keyword},
+	{token.SWITCH, "switch", keyword},
+	{token.TYPE, "type", keyword},
+	{token.VAR, "var", keyword},
+}
+
+const whitespace = "  \t  \n\n\n" // to separate tokens
+
+type testErrorHandler struct {
+	t *testing.T
+}
+
+func (h *testErrorHandler) Error(pos token.Position, msg string) {
+	h.t.Errorf("Error() called (msg = %s)", msg)
+}
+
+func newlineCount(s string) int {
+	n := 0
+	for i := 0; i < len(s); i++ {
+		if s[i] == '\n' {
+			n++
+		}
+	}
+	return n
+}
+
+func checkPos(t *testing.T, lit string, p token.Pos, expected token.Position) {
+	pos := fset.Position(p)
+	if pos.Filename != expected.Filename {
+		t.Errorf("bad filename for %q: got %s, expected %s", lit, pos.Filename, expected.Filename)
+	}
+	if pos.Offset != expected.Offset {
+		t.Errorf("bad position for %q: got %d, expected %d", lit, pos.Offset, expected.Offset)
+	}
+	if pos.Line != expected.Line {
+		t.Errorf("bad line for %q: got %d, expected %d", lit, pos.Line, expected.Line)
+	}
+	if pos.Column != expected.Column {
+		t.Errorf("bad column for %q: got %d, expected %d", lit, pos.Column, expected.Column)
+	}
+}
+
+// Verify that calling Scan() provides the correct results.
+func TestScan(t *testing.T) {
+	// make source
+	var src string
+	for _, e := range tokens {
+		src += e.lit + whitespace
+	}
+	src_linecount := newlineCount(src)
+	whitespace_linecount := newlineCount(whitespace)
+
+	// verify scan
+	var s Scanner
+	s.Init(fset.AddFile("", fset.Base(), len(src)), []byte(src), &testErrorHandler{t}, ScanComments)
+	index := 0
+	epos := token.Position{"", 0, 1, 1} // expected position
+	for {
+		pos, tok, lit := s.Scan()
+		e := elt{token.EOF, "", special}
+		if index < len(tokens) {
+			e = tokens[index]
+		}
+		if tok == token.EOF {
+			lit = "<EOF>"
+			epos.Line = src_linecount
+			epos.Column = 2
+		}
+		checkPos(t, lit, pos, epos)
+		if tok != e.tok {
+			t.Errorf("bad token for %q: got %s, expected %s", lit, tok.String(), e.tok.String())
+		}
+		if e.tok.IsLiteral() && lit != e.lit {
+			t.Errorf("bad literal for %q: got %q, expected %q", lit, lit, e.lit)
+		}
+		if tokenclass(tok) != e.class {
+			t.Errorf("bad class for %q: got %d, expected %d", lit, tokenclass(tok), e.class)
+		}
+		epos.Offset += len(lit) + len(whitespace)
+		epos.Line += newlineCount(lit) + whitespace_linecount
+		if tok == token.COMMENT && lit[1] == '/' {
+			// correct for unaccounted '/n' in //-style comment
+			epos.Offset++
+			epos.Line++
+		}
+		index++
+		if tok == token.EOF {
+			break
+		}
+	}
+	if s.ErrorCount != 0 {
+		t.Errorf("found %d errors", s.ErrorCount)
+	}
+}
+
+func checkSemi(t *testing.T, line string, mode uint) {
+	var S Scanner
+	file := fset.AddFile("TestSemis", fset.Base(), len(line))
+	S.Init(file, []byte(line), nil, mode)
+	pos, tok, lit := S.Scan()
+	for tok != token.EOF {
+		if tok == token.ILLEGAL {
+			// the illegal token literal indicates what
+			// kind of semicolon literal to expect
+			semiLit := "\n"
+			if lit[0] == '#' {
+				semiLit = ";"
+			}
+			// next token must be a semicolon
+			semiPos := file.Position(pos)
+			semiPos.Offset++
+			semiPos.Column++
+			pos, tok, lit = S.Scan()
+			if tok == token.SEMICOLON {
+				if lit != semiLit {
+					t.Errorf(`bad literal for %q: got %q, expected %q`, line, lit, semiLit)
+				}
+				checkPos(t, line, pos, semiPos)
+			} else {
+				t.Errorf("bad token for %q: got %s, expected ;", line, tok.String())
+			}
+		} else if tok == token.SEMICOLON {
+			t.Errorf("bad token for %q: got ;, expected no ;", line)
+		}
+		pos, tok, lit = S.Scan()
+	}
+}
+
+var lines = []string{
+	// # indicates a semicolon present in the source
+	// $ indicates an automatically inserted semicolon
+	"",
+	"#;",
+	"foo$\n",
+	"123$\n",
+	"1.2$\n",
+	"'x'$\n",
+	`"x"` + "$\n",
+	"`x`$\n",
+
+	"+\n",
+	"-\n",
+	"*\n",
+	"/\n",
+	"%\n",
+
+	"&\n",
+	"|\n",
+	"^\n",
+	"<<\n",
+	">>\n",
+	"&^\n",
+
+	"+=\n",
+	"-=\n",
+	"*=\n",
+	"/=\n",
+	"%=\n",
+
+	"&=\n",
+	"|=\n",
+	"^=\n",
+	"<<=\n",
+	">>=\n",
+	"&^=\n",
+
+	"&&\n",
+	"||\n",
+	"<-\n",
+	"++$\n",
+	"--$\n",
+
+	"==\n",
+	"<\n",
+	">\n",
+	"=\n",
+	"!\n",
+
+	"!=\n",
+	"<=\n",
+	">=\n",
+	":=\n",
+	"...\n",
+
+	"(\n",
+	"[\n",
+	"{\n",
+	",\n",
+	".\n",
+
+	")$\n",
+	"]$\n",
+	"}$\n",
+	"#;\n",
+	":\n",
+
+	"break$\n",
+	"case\n",
+	"chan\n",
+	"const\n",
+	"continue$\n",
+
+	"default\n",
+	"defer\n",
+	"else\n",
+	"fallthrough$\n",
+	"for\n",
+
+	"func\n",
+	"go\n",
+	"goto\n",
+	"if\n",
+	"import\n",
+
+	"interface\n",
+	"map\n",
+	"package\n",
+	"range\n",
+	"return$\n",
+
+	"select\n",
+	"struct\n",
+	"switch\n",
+	"type\n",
+	"var\n",
+
+	"foo$//comment\n",
+	"foo$//comment",
+	"foo$/*comment*/\n",
+	"foo$/*\n*/",
+	"foo$/*comment*/    \n",
+	"foo$/*\n*/    ",
+
+	"foo    $// comment\n",
+	"foo    $// comment",
+	"foo    $/*comment*/\n",
+	"foo    $/*\n*/",
+	"foo    $/*  */ /* \n */ bar$/**/\n",
+	"foo    $/*0*/ /*1*/ /*2*/\n",
+
+	"foo    $/*comment*/    \n",
+	"foo    $/*0*/ /*1*/ /*2*/    \n",
+	"foo	$/**/ /*-------------*/       /*----\n*/bar       $/*  \n*/baa$\n",
+	"foo    $/* an EOF terminates a line */",
+	"foo    $/* an EOF terminates a line */ /*",
+	"foo    $/* an EOF terminates a line */ //",
+
+	"package main$\n\nfunc main() {\n\tif {\n\t\treturn /* */ }$\n}$\n",
+	"package main$",
+}
+
+func TestSemis(t *testing.T) {
+	for _, line := range lines {
+		checkSemi(t, line, AllowIllegalChars|InsertSemis)
+		checkSemi(t, line, AllowIllegalChars|InsertSemis|ScanComments)
+
+		// if the input ended in newlines, the input must tokenize the
+		// same with or without those newlines
+		for i := len(line) - 1; i >= 0 && line[i] == '\n'; i-- {
+			checkSemi(t, line[0:i], AllowIllegalChars|InsertSemis)
+			checkSemi(t, line[0:i], AllowIllegalChars|InsertSemis|ScanComments)
+		}
+	}
+}
+
+type segment struct {
+	srcline  string // a line of source text
+	filename string // filename for current token
+	line     int    // line number for current token
+}
+
+var segments = []segment{
+	// exactly one token per line since the test consumes one token per segment
+	{"  line1", filepath.Join("dir", "TestLineComments"), 1},
+	{"\nline2", filepath.Join("dir", "TestLineComments"), 2},
+	{"\nline3  //line File1.go:100", filepath.Join("dir", "TestLineComments"), 3}, // bad line comment, ignored
+	{"\nline4", filepath.Join("dir", "TestLineComments"), 4},
+	{"\n//line File1.go:100\n  line100", filepath.Join("dir", "File1.go"), 100},
+	{"\n//line File2.go:200\n  line200", filepath.Join("dir", "File2.go"), 200},
+	{"\n//line :1\n  line1", "dir", 1},
+	{"\n//line foo:42\n  line42", filepath.Join("dir", "foo"), 42},
+	{"\n //line foo:42\n  line44", filepath.Join("dir", "foo"), 44},           // bad line comment, ignored
+	{"\n//line foo 42\n  line46", filepath.Join("dir", "foo"), 46},            // bad line comment, ignored
+	{"\n//line foo:42 extra text\n  line48", filepath.Join("dir", "foo"), 48}, // bad line comment, ignored
+	{"\n//line ./foo:42\n  line42", filepath.Join("dir", "foo"), 42},
+	{"\n//line a/b/c/File1.go:100\n  line100", filepath.Join("dir", "a", "b", "c", "File1.go"), 100},
+}
+
+var unixsegments = []segment{
+	{"\n//line /bar:42\n  line42", "/bar", 42},
+}
+
+var winsegments = []segment{
+	{"\n//line c:\\bar:42\n  line42", "c:\\bar", 42},
+	{"\n//line c:\\dir\\File1.go:100\n  line100", "c:\\dir\\File1.go", 100},
+}
+
+// Verify that comments of the form "//line filename:line" are interpreted correctly.
+func TestLineComments(t *testing.T) {
+	segs := segments
+	if runtime.GOOS == "windows" {
+		segs = append(segs, winsegments...)
+	} else {
+		segs = append(segs, unixsegments...)
+	}
+
+	// make source
+	var src string
+	for _, e := range segs {
+		src += e.srcline
+	}
+
+	// verify scan
+	var S Scanner
+	file := fset.AddFile(filepath.Join("dir", "TestLineComments"), fset.Base(), len(src))
+	S.Init(file, []byte(src), nil, 0)
+	for _, s := range segs {
+		p, _, lit := S.Scan()
+		pos := file.Position(p)
+		checkPos(t, lit, p, token.Position{s.filename, pos.Offset, s.line, pos.Column})
+	}
+
+	if S.ErrorCount != 0 {
+		t.Errorf("found %d errors", S.ErrorCount)
+	}
+}
+
+// Verify that initializing the same scanner more then once works correctly.
+func TestInit(t *testing.T) {
+	var s Scanner
+
+	// 1st init
+	src1 := "if true { }"
+	f1 := fset.AddFile("src1", fset.Base(), len(src1))
+	s.Init(f1, []byte(src1), nil, 0)
+	if f1.Size() != len(src1) {
+		t.Errorf("bad file size: got %d, expected %d", f1.Size(), len(src1))
+	}
+	s.Scan()              // if
+	s.Scan()              // true
+	_, tok, _ := s.Scan() // {
+	if tok != token.LBRACE {
+		t.Errorf("bad token: got %s, expected %s", tok.String(), token.LBRACE)
+	}
+
+	// 2nd init
+	src2 := "go true { ]"
+	f2 := fset.AddFile("src2", fset.Base(), len(src2))
+	s.Init(f2, []byte(src2), nil, 0)
+	if f2.Size() != len(src2) {
+		t.Errorf("bad file size: got %d, expected %d", f2.Size(), len(src2))
+	}
+	_, tok, _ = s.Scan() // go
+	if tok != token.GO {
+		t.Errorf("bad token: got %s, expected %s", tok.String(), token.GO)
+	}
+
+	if s.ErrorCount != 0 {
+		t.Errorf("found %d errors", s.ErrorCount)
+	}
+}
+
+func TestIllegalChars(t *testing.T) {
+	var s Scanner
+
+	const src = "*?*$*@*"
+	file := fset.AddFile("", fset.Base(), len(src))
+	s.Init(file, []byte(src), &testErrorHandler{t}, AllowIllegalChars)
+	for offs, ch := range src {
+		pos, tok, lit := s.Scan()
+		if poffs := file.Offset(pos); poffs != offs {
+			t.Errorf("bad position for %s: got %d, expected %d", lit, poffs, offs)
+		}
+		if tok == token.ILLEGAL && lit != string(ch) {
+			t.Errorf("bad token: got %s, expected %s", lit, string(ch))
+		}
+	}
+
+	if s.ErrorCount != 0 {
+		t.Errorf("found %d errors", s.ErrorCount)
+	}
+}
+
+func TestStdErrorHander(t *testing.T) {
+	const src = "@\n" + // illegal character, cause an error
+		"@ @\n" + // two errors on the same line
+		"//line File2:20\n" +
+		"@\n" + // different file, but same line
+		"//line File2:1\n" +
+		"@ @\n" + // same file, decreasing line number
+		"//line File1:1\n" +
+		"@ @ @" // original file, line 1 again
+
+	v := new(ErrorVector)
+	var s Scanner
+	s.Init(fset.AddFile("File1", fset.Base(), len(src)), []byte(src), v, 0)
+	for {
+		if _, tok, _ := s.Scan(); tok == token.EOF {
+			break
+		}
+	}
+
+	list := v.GetErrorList(Raw)
+	if len(list) != 9 {
+		t.Errorf("found %d raw errors, expected 9", len(list))
+		PrintError(os.Stderr, list)
+	}
+
+	list = v.GetErrorList(Sorted)
+	if len(list) != 9 {
+		t.Errorf("found %d sorted errors, expected 9", len(list))
+		PrintError(os.Stderr, list)
+	}
+
+	list = v.GetErrorList(NoMultiples)
+	if len(list) != 4 {
+		t.Errorf("found %d one-per-line errors, expected 4", len(list))
+		PrintError(os.Stderr, list)
+	}
+
+	if v.ErrorCount() != s.ErrorCount {
+		t.Errorf("found %d errors, expected %d", v.ErrorCount(), s.ErrorCount)
+	}
+}
+
+type errorCollector struct {
+	cnt int            // number of errors encountered
+	msg string         // last error message encountered
+	pos token.Position // last error position encountered
+}
+
+func (h *errorCollector) Error(pos token.Position, msg string) {
+	h.cnt++
+	h.msg = msg
+	h.pos = pos
+}
+
+func checkError(t *testing.T, src string, tok token.Token, pos int, err string) {
+	var s Scanner
+	var h errorCollector
+	s.Init(fset.AddFile("", fset.Base(), len(src)), []byte(src), &h, ScanComments)
+	_, tok0, _ := s.Scan()
+	_, tok1, _ := s.Scan()
+	if tok0 != tok {
+		t.Errorf("%q: got %s, expected %s", src, tok0, tok)
+	}
+	if tok1 != token.EOF {
+		t.Errorf("%q: got %s, expected EOF", src, tok1)
+	}
+	cnt := 0
+	if err != "" {
+		cnt = 1
+	}
+	if h.cnt != cnt {
+		t.Errorf("%q: got cnt %d, expected %d", src, h.cnt, cnt)
+	}
+	if h.msg != err {
+		t.Errorf("%q: got msg %q, expected %q", src, h.msg, err)
+	}
+	if h.pos.Offset != pos {
+		t.Errorf("%q: got offset %d, expected %d", src, h.pos.Offset, pos)
+	}
+}
+
+var errors = []struct {
+	src string
+	tok token.Token
+	pos int
+	err string
+}{
+	{"\a", token.ILLEGAL, 0, "illegal character U+0007"},
+	{`#`, token.ILLEGAL, 0, "illegal character U+0023 '#'"},
+	{`…`, token.ILLEGAL, 0, "illegal character U+2026 '…'"},
+	{`' '`, token.CHAR, 0, ""},
+	{`''`, token.CHAR, 0, "illegal character literal"},
+	{`'\8'`, token.CHAR, 2, "unknown escape sequence"},
+	{`'\08'`, token.CHAR, 3, "illegal character in escape sequence"},
+	{`'\x0g'`, token.CHAR, 4, "illegal character in escape sequence"},
+	{`'\Uffffffff'`, token.CHAR, 2, "escape sequence is invalid Unicode code point"},
+	{`'`, token.CHAR, 0, "character literal not terminated"},
+	{`""`, token.STRING, 0, ""},
+	{`"`, token.STRING, 0, "string not terminated"},
+	{"``", token.STRING, 0, ""},
+	{"`", token.STRING, 0, "string not terminated"},
+	{"/**/", token.COMMENT, 0, ""},
+	{"/*", token.COMMENT, 0, "comment not terminated"},
+	{"077", token.INT, 0, ""},
+	{"078.", token.FLOAT, 0, ""},
+	{"07801234567.", token.FLOAT, 0, ""},
+	{"078e0", token.FLOAT, 0, ""},
+	{"078", token.INT, 0, "illegal octal number"},
+	{"07800000009", token.INT, 0, "illegal octal number"},
+	{"0x", token.INT, 0, "illegal hexadecimal number"},
+	{"0X", token.INT, 0, "illegal hexadecimal number"},
+	{"\"abc\x00def\"", token.STRING, 4, "illegal character NUL"},
+	{"\"abc\x80def\"", token.STRING, 4, "illegal UTF-8 encoding"},
+}
+
+func TestScanErrors(t *testing.T) {
+	for _, e := range errors {
+		checkError(t, e.src, e.tok, e.pos, e.err)
+	}
+}
diff --git a/src/pkg/go/token/Makefile b/src/pkg/go/token/Makefile
new file mode 100644
index 000000000..4a4e64dc8
--- /dev/null
+++ b/src/pkg/go/token/Makefile
@@ -0,0 +1,12 @@
+# Copyright 2009 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../Make.inc
+
+TARG=go/token
+GOFILES=\
+	position.go\
+	token.go\
+
+include ../../../Make.pkg
diff --git a/src/pkg/go/token/position.go b/src/pkg/go/token/position.go
new file mode 100644
index 000000000..c559e19f8
--- /dev/null
+++ b/src/pkg/go/token/position.go
@@ -0,0 +1,424 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// TODO(gri) consider making this a separate package outside the go directory.
+
+package token
+
+import (
+	"fmt"
+	"sort"
+	"sync"
+)
+
+// Position describes an arbitrary source position
+// including the file, line, and column location.
+// A Position is valid if the line number is > 0.
+//
+type Position struct {
+	Filename string // filename, if any
+	Offset   int    // offset, starting at 0
+	Line     int    // line number, starting at 1
+	Column   int    // column number, starting at 1 (character count)
+}
+
+// IsValid returns true if the position is valid.
+func (pos *Position) IsValid() bool { return pos.Line > 0 }
+
+// String returns a string in one of several forms:
+//
+//	file:line:column    valid position with file name
+//	line:column         valid position without file name
+//	file                invalid position with file name
+//	-                   invalid position without file name
+//
+func (pos Position) String() string {
+	s := pos.Filename
+	if pos.IsValid() {
+		if s != "" {
+			s += ":"
+		}
+		s += fmt.Sprintf("%d:%d", pos.Line, pos.Column)
+	}
+	if s == "" {
+		s = "-"
+	}
+	return s
+}
+
+// Pos is a compact encoding of a source position within a file set.
+// It can be converted into a Position for a more convenient, but much
+// larger, representation.
+//
+// The Pos value for a given file is a number in the range [base, base+size],
+// where base and size are specified when adding the file to the file set via
+// AddFile.
+//
+// To create the Pos value for a specific source offset, first add
+// the respective file to the current file set (via FileSet.AddFile)
+// and then call File.Pos(offset) for that file. Given a Pos value p
+// for a specific file set fset, the corresponding Position value is
+// obtained by calling fset.Position(p).
+//
+// Pos values can be compared directly with the usual comparison operators:
+// If two Pos values p and q are in the same file, comparing p and q is
+// equivalent to comparing the respective source file offsets. If p and q
+// are in different files, p < q is true if the file implied by p was added
+// to the respective file set before the file implied by q.
+//
+type Pos int
+
+// The zero value for Pos is NoPos; there is no file and line information
+// associated with it, and NoPos().IsValid() is false. NoPos is always
+// smaller than any other Pos value. The corresponding Position value
+// for NoPos is the zero value for Position.
+// 
+const NoPos Pos = 0
+
+// IsValid returns true if the position is valid.
+func (p Pos) IsValid() bool {
+	return p != NoPos
+}
+
+func searchFiles(a []*File, x int) int {
+	return sort.Search(len(a), func(i int) bool { return a[i].base > x }) - 1
+}
+
+func (s *FileSet) file(p Pos) *File {
+	if f := s.last; f != nil && f.base <= int(p) && int(p) <= f.base+f.size {
+		return f
+	}
+	if i := searchFiles(s.files, int(p)); i >= 0 {
+		f := s.files[i]
+		// f.base <= int(p) by definition of searchFiles
+		if int(p) <= f.base+f.size {
+			s.last = f
+			return f
+		}
+	}
+	return nil
+}
+
+// File returns the file which contains the position p.
+// If no such file is found (for instance for p == NoPos),
+// the result is nil.
+//
+func (s *FileSet) File(p Pos) (f *File) {
+	if p != NoPos {
+		s.mutex.RLock()
+		f = s.file(p)
+		s.mutex.RUnlock()
+	}
+	return
+}
+
+func (f *File) position(p Pos) (pos Position) {
+	offset := int(p) - f.base
+	pos.Offset = offset
+	pos.Filename, pos.Line, pos.Column = f.info(offset)
+	return
+}
+
+// Position converts a Pos in the fileset into a general Position.
+func (s *FileSet) Position(p Pos) (pos Position) {
+	if p != NoPos {
+		// TODO(gri) consider optimizing the case where p
+		//           is in the last file added, or perhaps
+		//           looked at - will eliminate one level
+		//           of search
+		s.mutex.RLock()
+		if f := s.file(p); f != nil {
+			pos = f.position(p)
+		}
+		s.mutex.RUnlock()
+	}
+	return
+}
+
+type lineInfo struct {
+	offset   int
+	filename string
+	line     int
+}
+
+// AddLineInfo adds alternative file and line number information for
+// a given file offset. The offset must be larger than the offset for
+// the previously added alternative line info and smaller than the
+// file size; otherwise the information is ignored.
+//
+// AddLineInfo is typically used to register alternative position
+// information for //line filename:line comments in source files.
+//
+func (f *File) AddLineInfo(offset int, filename string, line int) {
+	f.set.mutex.Lock()
+	if i := len(f.infos); i == 0 || f.infos[i-1].offset < offset && offset < f.size {
+		f.infos = append(f.infos, lineInfo{offset, filename, line})
+	}
+	f.set.mutex.Unlock()
+}
+
+// A File is a handle for a file belonging to a FileSet.
+// A File has a name, size, and line offset table.
+//
+type File struct {
+	set  *FileSet
+	name string // file name as provided to AddFile
+	base int    // Pos value range for this file is [base...base+size]
+	size int    // file size as provided to AddFile
+
+	// lines and infos are protected by set.mutex
+	lines []int
+	infos []lineInfo
+}
+
+// Name returns the file name of file f as registered with AddFile.
+func (f *File) Name() string {
+	return f.name
+}
+
+// Base returns the base offset of file f as registered with AddFile.
+func (f *File) Base() int {
+	return f.base
+}
+
+// Size returns the size of file f as registered with AddFile.
+func (f *File) Size() int {
+	return f.size
+}
+
+// LineCount returns the number of lines in file f.
+func (f *File) LineCount() int {
+	f.set.mutex.RLock()
+	n := len(f.lines)
+	f.set.mutex.RUnlock()
+	return n
+}
+
+// AddLine adds the line offset for a new line.
+// The line offset must be larger than the offset for the previous line
+// and smaller than the file size; otherwise the line offset is ignored.
+//
+func (f *File) AddLine(offset int) {
+	f.set.mutex.Lock()
+	if i := len(f.lines); (i == 0 || f.lines[i-1] < offset) && offset < f.size {
+		f.lines = append(f.lines, offset)
+	}
+	f.set.mutex.Unlock()
+}
+
+// SetLines sets the line offsets for a file and returns true if successful.
+// The line offsets are the offsets of the first character of each line;
+// for instance for the content "ab\nc\n" the line offsets are {0, 3}.
+// An empty file has an empty line offset table.
+// Each line offset must be larger than the offset for the previous line
+// and smaller than the file size; otherwise SetLines fails and returns
+// false.
+//
+func (f *File) SetLines(lines []int) bool {
+	// verify validity of lines table
+	size := f.size
+	for i, offset := range lines {
+		if i > 0 && offset <= lines[i-1] || size <= offset {
+			return false
+		}
+	}
+
+	// set lines table
+	f.set.mutex.Lock()
+	f.lines = lines
+	f.set.mutex.Unlock()
+	return true
+}
+
+// SetLinesForContent sets the line offsets for the given file content.
+func (f *File) SetLinesForContent(content []byte) {
+	var lines []int
+	line := 0
+	for offset, b := range content {
+		if line >= 0 {
+			lines = append(lines, line)
+		}
+		line = -1
+		if b == '\n' {
+			line = offset + 1
+		}
+	}
+
+	// set lines table
+	f.set.mutex.Lock()
+	f.lines = lines
+	f.set.mutex.Unlock()
+}
+
+// Pos returns the Pos value for the given file offset;
+// the offset must be <= f.Size().
+// f.Pos(f.Offset(p)) == p.
+//
+func (f *File) Pos(offset int) Pos {
+	if offset > f.size {
+		panic("illegal file offset")
+	}
+	return Pos(f.base + offset)
+}
+
+// Offset returns the offset for the given file position p;
+// p must be a valid Pos value in that file.
+// f.Offset(f.Pos(offset)) == offset.
+//
+func (f *File) Offset(p Pos) int {
+	if int(p) < f.base || int(p) > f.base+f.size {
+		panic("illegal Pos value")
+	}
+	return int(p) - f.base
+}
+
+// Line returns the line number for the given file position p;
+// p must be a Pos value in that file or NoPos.
+//
+func (f *File) Line(p Pos) int {
+	// TODO(gri) this can be implemented much more efficiently
+	return f.Position(p).Line
+}
+
+// Position returns the Position value for the given file position p;
+// p must be a Pos value in that file or NoPos.
+//
+func (f *File) Position(p Pos) (pos Position) {
+	if p != NoPos {
+		if int(p) < f.base || int(p) > f.base+f.size {
+			panic("illegal Pos value")
+		}
+		pos = f.position(p)
+	}
+	return
+}
+
+func searchInts(a []int, x int) int {
+	// This function body is a manually inlined version of:
+	//
+	//   return sort.Search(len(a), func(i int) bool { return a[i] > x }) - 1
+	//
+	// With better compiler optimizations, this may not be needed in the
+	// future, but at the moment this change improves the go/printer
+	// benchmark performance by ~30%. This has a direct impact on the
+	// speed of gofmt and thus seems worthwhile (2011-04-29).
+	i, j := 0, len(a)
+	for i < j {
+		h := i + (j-i)/2 // avoid overflow when computing h
+		// i ≤ h < j
+		if a[h] <= x {
+			i = h + 1
+		} else {
+			j = h
+		}
+	}
+	return i - 1
+}
+
+func searchLineInfos(a []lineInfo, x int) int {
+	return sort.Search(len(a), func(i int) bool { return a[i].offset > x }) - 1
+}
+
+// info returns the file name, line, and column number for a file offset.
+func (f *File) info(offset int) (filename string, line, column int) {
+	filename = f.name
+	if i := searchInts(f.lines, offset); i >= 0 {
+		line, column = i+1, offset-f.lines[i]+1
+	}
+	if len(f.infos) > 0 {
+		// almost no files have extra line infos
+		if i := searchLineInfos(f.infos, offset); i >= 0 {
+			alt := &f.infos[i]
+			filename = alt.filename
+			if i := searchInts(f.lines, alt.offset); i >= 0 {
+				line += alt.line - i - 1
+			}
+		}
+	}
+	return
+}
+
+// A FileSet represents a set of source files.
+// Methods of file sets are synchronized; multiple goroutines
+// may invoke them concurrently.
+//
+type FileSet struct {
+	mutex sync.RWMutex // protects the file set
+	base  int          // base offset for the next file
+	files []*File      // list of files in the order added to the set
+	last  *File        // cache of last file looked up
+}
+
+// NewFileSet creates a new file set.
+func NewFileSet() *FileSet {
+	s := new(FileSet)
+	s.base = 1 // 0 == NoPos
+	return s
+}
+
+// Base returns the minimum base offset that must be provided to
+// AddFile when adding the next file.
+//
+func (s *FileSet) Base() int {
+	s.mutex.RLock()
+	b := s.base
+	s.mutex.RUnlock()
+	return b
+
+}
+
+// AddFile adds a new file with a given filename, base offset, and file size
+// to the file set s and returns the file. Multiple files may have the same
+// name. The base offset must not be smaller than the FileSet's Base(), and
+// size must not be negative.
+//
+// Adding the file will set the file set's Base() value to base + size + 1
+// as the minimum base value for the next file. The following relationship
+// exists between a Pos value p for a given file offset offs:
+//
+//	int(p) = base + offs
+//
+// with offs in the range [0, size] and thus p in the range [base, base+size].
+// For convenience, File.Pos may be used to create file-specific position
+// values from a file offset.
+//
+func (s *FileSet) AddFile(filename string, base, size int) *File {
+	s.mutex.Lock()
+	defer s.mutex.Unlock()
+	if base < s.base || size < 0 {
+		panic("illegal base or size")
+	}
+	// base >= s.base && size >= 0
+	f := &File{s, filename, base, size, []int{0}, nil}
+	base += size + 1 // +1 because EOF also has a position
+	if base < 0 {
+		panic("token.Pos offset overflow (> 2G of source code in file set)")
+	}
+	// add the file to the file set
+	s.base = base
+	s.files = append(s.files, f)
+	s.last = f
+	return f
+}
+
+// Files returns the files added to the file set.
+func (s *FileSet) Files() <-chan *File {
+	ch := make(chan *File)
+	go func() {
+		for i := 0; ; i++ {
+			var f *File
+			s.mutex.RLock()
+			if i < len(s.files) {
+				f = s.files[i]
+			}
+			s.mutex.RUnlock()
+			if f == nil {
+				break
+			}
+			ch <- f
+		}
+		close(ch)
+	}()
+	return ch
+}
diff --git a/src/pkg/go/token/position_test.go b/src/pkg/go/token/position_test.go
new file mode 100644
index 000000000..30bec5991
--- /dev/null
+++ b/src/pkg/go/token/position_test.go
@@ -0,0 +1,180 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package token
+
+import (
+	"fmt"
+	"testing"
+)
+
+func checkPos(t *testing.T, msg string, p, q Position) {
+	if p.Filename != q.Filename {
+		t.Errorf("%s: expected filename = %q; got %q", msg, q.Filename, p.Filename)
+	}
+	if p.Offset != q.Offset {
+		t.Errorf("%s: expected offset = %d; got %d", msg, q.Offset, p.Offset)
+	}
+	if p.Line != q.Line {
+		t.Errorf("%s: expected line = %d; got %d", msg, q.Line, p.Line)
+	}
+	if p.Column != q.Column {
+		t.Errorf("%s: expected column = %d; got %d", msg, q.Column, p.Column)
+	}
+}
+
+func TestNoPos(t *testing.T) {
+	if NoPos.IsValid() {
+		t.Errorf("NoPos should not be valid")
+	}
+	var fset *FileSet
+	checkPos(t, "nil NoPos", fset.Position(NoPos), Position{})
+	fset = NewFileSet()
+	checkPos(t, "fset NoPos", fset.Position(NoPos), Position{})
+}
+
+var tests = []struct {
+	filename string
+	source   []byte // may be nil
+	size     int
+	lines    []int
+}{
+	{"a", []byte{}, 0, []int{}},
+	{"b", []byte("01234"), 5, []int{0}},
+	{"c", []byte("\n\n\n\n\n\n\n\n\n"), 9, []int{0, 1, 2, 3, 4, 5, 6, 7, 8}},
+	{"d", nil, 100, []int{0, 5, 10, 20, 30, 70, 71, 72, 80, 85, 90, 99}},
+	{"e", nil, 777, []int{0, 80, 100, 120, 130, 180, 267, 455, 500, 567, 620}},
+	{"f", []byte("package p\n\nimport \"fmt\""), 23, []int{0, 10, 11}},
+	{"g", []byte("package p\n\nimport \"fmt\"\n"), 24, []int{0, 10, 11}},
+	{"h", []byte("package p\n\nimport \"fmt\"\n "), 25, []int{0, 10, 11, 24}},
+}
+
+func linecol(lines []int, offs int) (int, int) {
+	prevLineOffs := 0
+	for line, lineOffs := range lines {
+		if offs < lineOffs {
+			return line, offs - prevLineOffs + 1
+		}
+		prevLineOffs = lineOffs
+	}
+	return len(lines), offs - prevLineOffs + 1
+}
+
+func verifyPositions(t *testing.T, fset *FileSet, f *File, lines []int) {
+	for offs := 0; offs < f.Size(); offs++ {
+		p := f.Pos(offs)
+		offs2 := f.Offset(p)
+		if offs2 != offs {
+			t.Errorf("%s, Offset: expected offset %d; got %d", f.Name(), offs, offs2)
+		}
+		line, col := linecol(lines, offs)
+		msg := fmt.Sprintf("%s (offs = %d, p = %d)", f.Name(), offs, p)
+		checkPos(t, msg, f.Position(f.Pos(offs)), Position{f.Name(), offs, line, col})
+		checkPos(t, msg, fset.Position(p), Position{f.Name(), offs, line, col})
+	}
+}
+
+func makeTestSource(size int, lines []int) []byte {
+	src := make([]byte, size)
+	for _, offs := range lines {
+		if offs > 0 {
+			src[offs-1] = '\n'
+		}
+	}
+	return src
+}
+
+func TestPositions(t *testing.T) {
+	const delta = 7 // a non-zero base offset increment
+	fset := NewFileSet()
+	for _, test := range tests {
+		// verify consistency of test case
+		if test.source != nil && len(test.source) != test.size {
+			t.Errorf("%s: inconsistent test case: expected file size %d; got %d", test.filename, test.size, len(test.source))
+		}
+
+		// add file and verify name and size
+		f := fset.AddFile(test.filename, fset.Base()+delta, test.size)
+		if f.Name() != test.filename {
+			t.Errorf("expected filename %q; got %q", test.filename, f.Name())
+		}
+		if f.Size() != test.size {
+			t.Errorf("%s: expected file size %d; got %d", f.Name(), test.size, f.Size())
+		}
+		if fset.File(f.Pos(0)) != f {
+			t.Errorf("%s: f.Pos(0) was not found in f", f.Name())
+		}
+
+		// add lines individually and verify all positions
+		for i, offset := range test.lines {
+			f.AddLine(offset)
+			if f.LineCount() != i+1 {
+				t.Errorf("%s, AddLine: expected line count %d; got %d", f.Name(), i+1, f.LineCount())
+			}
+			// adding the same offset again should be ignored
+			f.AddLine(offset)
+			if f.LineCount() != i+1 {
+				t.Errorf("%s, AddLine: expected unchanged line count %d; got %d", f.Name(), i+1, f.LineCount())
+			}
+			verifyPositions(t, fset, f, test.lines[0:i+1])
+		}
+
+		// add lines with SetLines and verify all positions
+		if ok := f.SetLines(test.lines); !ok {
+			t.Errorf("%s: SetLines failed", f.Name())
+		}
+		if f.LineCount() != len(test.lines) {
+			t.Errorf("%s, SetLines: expected line count %d; got %d", f.Name(), len(test.lines), f.LineCount())
+		}
+		verifyPositions(t, fset, f, test.lines)
+
+		// add lines with SetLinesForContent and verify all positions
+		src := test.source
+		if src == nil {
+			// no test source available - create one from scratch
+			src = makeTestSource(test.size, test.lines)
+		}
+		f.SetLinesForContent(src)
+		if f.LineCount() != len(test.lines) {
+			t.Errorf("%s, SetLinesForContent: expected line count %d; got %d", f.Name(), len(test.lines), f.LineCount())
+		}
+		verifyPositions(t, fset, f, test.lines)
+	}
+}
+
+func TestLineInfo(t *testing.T) {
+	fset := NewFileSet()
+	f := fset.AddFile("foo", fset.Base(), 500)
+	lines := []int{0, 42, 77, 100, 210, 220, 277, 300, 333, 401}
+	// add lines individually and provide alternative line information
+	for _, offs := range lines {
+		f.AddLine(offs)
+		f.AddLineInfo(offs, "bar", 42)
+	}
+	// verify positions for all offsets
+	for offs := 0; offs <= f.Size(); offs++ {
+		p := f.Pos(offs)
+		_, col := linecol(lines, offs)
+		msg := fmt.Sprintf("%s (offs = %d, p = %d)", f.Name(), offs, p)
+		checkPos(t, msg, f.Position(f.Pos(offs)), Position{"bar", offs, 42, col})
+		checkPos(t, msg, fset.Position(p), Position{"bar", offs, 42, col})
+	}
+}
+
+func TestFiles(t *testing.T) {
+	fset := NewFileSet()
+	for i, test := range tests {
+		fset.AddFile(test.filename, fset.Base(), test.size)
+		j := 0
+		for g := range fset.Files() {
+			if g.Name() != tests[j].filename {
+				t.Errorf("expected filename = %s; got %s", tests[j].filename, g.Name())
+			}
+			j++
+		}
+		if j != i+1 {
+			t.Errorf("expected %d files; got %d", i+1, j)
+		}
+	}
+}
diff --git a/src/pkg/go/token/token.go b/src/pkg/go/token/token.go
new file mode 100644
index 000000000..557374052
--- /dev/null
+++ b/src/pkg/go/token/token.go
@@ -0,0 +1,310 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package token defines constants representing the lexical tokens of the Go
+// programming language and basic operations on tokens (printing, predicates).
+//
+package token
+
+import "strconv"
+
+// Token is the set of lexical tokens of the Go programming language.
+type Token int
+
+// The list of tokens.
+const (
+	// Special tokens
+	ILLEGAL Token = iota
+	EOF
+	COMMENT
+
+	literal_beg
+	// Identifiers and basic type literals
+	// (these tokens stand for classes of literals)
+	IDENT  // main
+	INT    // 12345
+	FLOAT  // 123.45
+	IMAG   // 123.45i
+	CHAR   // 'a'
+	STRING // "abc"
+	literal_end
+
+	operator_beg
+	// Operators and delimiters
+	ADD // +
+	SUB // -
+	MUL // *
+	QUO // /
+	REM // %
+
+	AND     // &
+	OR      // |
+	XOR     // ^
+	SHL     // <<
+	SHR     // >>
+	AND_NOT // &^
+
+	ADD_ASSIGN // +=
+	SUB_ASSIGN // -=
+	MUL_ASSIGN // *=
+	QUO_ASSIGN // /=
+	REM_ASSIGN // %=
+
+	AND_ASSIGN     // &=
+	OR_ASSIGN      // |=
+	XOR_ASSIGN     // ^=
+	SHL_ASSIGN     // <<=
+	SHR_ASSIGN     // >>=
+	AND_NOT_ASSIGN // &^=
+
+	LAND  // &&
+	LOR   // ||
+	ARROW // <-
+	INC   // ++
+	DEC   // --
+
+	EQL    // ==
+	LSS    // <
+	GTR    // >
+	ASSIGN // =
+	NOT    // !
+
+	NEQ      // !=
+	LEQ      // <=
+	GEQ      // >=
+	DEFINE   // :=
+	ELLIPSIS // ...
+
+	LPAREN // (
+	LBRACK // [
+	LBRACE // {
+	COMMA  // ,
+	PERIOD // .
+
+	RPAREN    // )
+	RBRACK    // ]
+	RBRACE    // }
+	SEMICOLON // ;
+	COLON     // :
+	operator_end
+
+	keyword_beg
+	// Keywords
+	BREAK
+	CASE
+	CHAN
+	CONST
+	CONTINUE
+
+	DEFAULT
+	DEFER
+	ELSE
+	FALLTHROUGH
+	FOR
+
+	FUNC
+	GO
+	GOTO
+	IF
+	IMPORT
+
+	INTERFACE
+	MAP
+	PACKAGE
+	RANGE
+	RETURN
+
+	SELECT
+	STRUCT
+	SWITCH
+	TYPE
+	VAR
+	keyword_end
+)
+
+var tokens = [...]string{
+	ILLEGAL: "ILLEGAL",
+
+	EOF:     "EOF",
+	COMMENT: "COMMENT",
+
+	IDENT:  "IDENT",
+	INT:    "INT",
+	FLOAT:  "FLOAT",
+	IMAG:   "IMAG",
+	CHAR:   "CHAR",
+	STRING: "STRING",
+
+	ADD: "+",
+	SUB: "-",
+	MUL: "*",
+	QUO: "/",
+	REM: "%",
+
+	AND:     "&",
+	OR:      "|",
+	XOR:     "^",
+	SHL:     "<<",
+	SHR:     ">>",
+	AND_NOT: "&^",
+
+	ADD_ASSIGN: "+=",
+	SUB_ASSIGN: "-=",
+	MUL_ASSIGN: "*=",
+	QUO_ASSIGN: "/=",
+	REM_ASSIGN: "%=",
+
+	AND_ASSIGN:     "&=",
+	OR_ASSIGN:      "|=",
+	XOR_ASSIGN:     "^=",
+	SHL_ASSIGN:     "<<=",
+	SHR_ASSIGN:     ">>=",
+	AND_NOT_ASSIGN: "&^=",
+
+	LAND:  "&&",
+	LOR:   "||",
+	ARROW: "<-",
+	INC:   "++",
+	DEC:   "--",
+
+	EQL:    "==",
+	LSS:    "<",
+	GTR:    ">",
+	ASSIGN: "=",
+	NOT:    "!",
+
+	NEQ:      "!=",
+	LEQ:      "<=",
+	GEQ:      ">=",
+	DEFINE:   ":=",
+	ELLIPSIS: "...",
+
+	LPAREN: "(",
+	LBRACK: "[",
+	LBRACE: "{",
+	COMMA:  ",",
+	PERIOD: ".",
+
+	RPAREN:    ")",
+	RBRACK:    "]",
+	RBRACE:    "}",
+	SEMICOLON: ";",
+	COLON:     ":",
+
+	BREAK:    "break",
+	CASE:     "case",
+	CHAN:     "chan",
+	CONST:    "const",
+	CONTINUE: "continue",
+
+	DEFAULT:     "default",
+	DEFER:       "defer",
+	ELSE:        "else",
+	FALLTHROUGH: "fallthrough",
+	FOR:         "for",
+
+	FUNC:   "func",
+	GO:     "go",
+	GOTO:   "goto",
+	IF:     "if",
+	IMPORT: "import",
+
+	INTERFACE: "interface",
+	MAP:       "map",
+	PACKAGE:   "package",
+	RANGE:     "range",
+	RETURN:    "return",
+
+	SELECT: "select",
+	STRUCT: "struct",
+	SWITCH: "switch",
+	TYPE:   "type",
+	VAR:    "var",
+}
+
+// String returns the string corresponding to the token tok.
+// For operators, delimiters, and keywords the string is the actual
+// token character sequence (e.g., for the token ADD, the string is
+// "+"). For all other tokens the string corresponds to the token
+// constant name (e.g. for the token IDENT, the string is "IDENT").
+//
+func (tok Token) String() string {
+	s := ""
+	if 0 <= tok && tok < Token(len(tokens)) {
+		s = tokens[tok]
+	}
+	if s == "" {
+		s = "token(" + strconv.Itoa(int(tok)) + ")"
+	}
+	return s
+}
+
+// A set of constants for precedence-based expression parsing.
+// Non-operators have lowest precedence, followed by operators
+// starting with precedence 1 up to unary operators. The highest
+// precedence corresponds serves as "catch-all" precedence for
+// selector, indexing, and other operator and delimiter tokens.
+//
+const (
+	LowestPrec  = 0 // non-operators
+	UnaryPrec   = 6
+	HighestPrec = 7
+)
+
+// Precedence returns the operator precedence of the binary
+// operator op. If op is not a binary operator, the result
+// is LowestPrecedence.
+//
+func (op Token) Precedence() int {
+	switch op {
+	case LOR:
+		return 1
+	case LAND:
+		return 2
+	case EQL, NEQ, LSS, LEQ, GTR, GEQ:
+		return 3
+	case ADD, SUB, OR, XOR:
+		return 4
+	case MUL, QUO, REM, SHL, SHR, AND, AND_NOT:
+		return 5
+	}
+	return LowestPrec
+}
+
+var keywords map[string]Token
+
+func init() {
+	keywords = make(map[string]Token)
+	for i := keyword_beg + 1; i < keyword_end; i++ {
+		keywords[tokens[i]] = i
+	}
+}
+
+// Lookup maps an identifier to its keyword token or IDENT (if not a keyword).
+//
+func Lookup(ident []byte) Token {
+	// TODO Maps with []byte key are illegal because []byte does not
+	//      support == . Should find a more efficient solution eventually.
+	if tok, is_keyword := keywords[string(ident)]; is_keyword {
+		return tok
+	}
+	return IDENT
+}
+
+// Predicates
+
+// IsLiteral returns true for tokens corresponding to identifiers
+// and basic type literals; returns false otherwise.
+//
+func (tok Token) IsLiteral() bool { return literal_beg < tok && tok < literal_end }
+
+// IsOperator returns true for tokens corresponding to operators and
+// delimiters; returns false otherwise.
+//
+func (tok Token) IsOperator() bool { return operator_beg < tok && tok < operator_end }
+
+// IsKeyword returns true for tokens corresponding to keywords;
+// returns false otherwise.
+//
+func (tok Token) IsKeyword() bool { return keyword_beg < tok && tok < keyword_end }
diff --git a/src/pkg/go/typechecker/Makefile b/src/pkg/go/typechecker/Makefile
new file mode 100644
index 000000000..83af3ef4e
--- /dev/null
+++ b/src/pkg/go/typechecker/Makefile
@@ -0,0 +1,14 @@
+# Copyright 2010 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../Make.inc
+
+TARG=go/typechecker
+GOFILES=\
+	scope.go\
+	type.go\
+	typechecker.go\
+	universe.go\
+
+include ../../../Make.pkg
diff --git a/src/pkg/go/typechecker/scope.go b/src/pkg/go/typechecker/scope.go
new file mode 100644
index 000000000..d73d1a450
--- /dev/null
+++ b/src/pkg/go/typechecker/scope.go
@@ -0,0 +1,69 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// DEPRECATED FILE - WILL GO AWAY EVENTUALLY.
+//
+// Scope handling is now done in go/parser.
+// The functionality here is only present to
+// keep the typechecker running for now.
+
+package typechecker
+
+import "go/ast"
+
+func (tc *typechecker) openScope() *ast.Scope {
+	tc.topScope = ast.NewScope(tc.topScope)
+	return tc.topScope
+}
+
+func (tc *typechecker) closeScope() {
+	tc.topScope = tc.topScope.Outer
+}
+
+// declInScope declares an object of a given kind and name in scope and sets the object's Decl and N fields.
+// It returns the newly allocated object. If an object with the same name already exists in scope, an error
+// is reported and the object is not inserted.
+func (tc *typechecker) declInScope(scope *ast.Scope, kind ast.ObjKind, name *ast.Ident, decl interface{}, n int) *ast.Object {
+	obj := ast.NewObj(kind, name.Name)
+	obj.Decl = decl
+	//obj.N = n
+	name.Obj = obj
+	if name.Name != "_" {
+		if alt := scope.Insert(obj); alt != nil {
+			tc.Errorf(name.Pos(), "%s already declared at %s", name.Name, tc.fset.Position(alt.Pos()).String())
+		}
+	}
+	return obj
+}
+
+// decl is the same as declInScope(tc.topScope, ...)
+func (tc *typechecker) decl(kind ast.ObjKind, name *ast.Ident, decl interface{}, n int) *ast.Object {
+	return tc.declInScope(tc.topScope, kind, name, decl, n)
+}
+
+// find returns the object with the given name if visible in the current scope hierarchy.
+// If no such object is found, an error is reported and a bad object is returned instead.
+func (tc *typechecker) find(name *ast.Ident) (obj *ast.Object) {
+	for s := tc.topScope; s != nil && obj == nil; s = s.Outer {
+		obj = s.Lookup(name.Name)
+	}
+	if obj == nil {
+		tc.Errorf(name.Pos(), "%s not declared", name.Name)
+		obj = ast.NewObj(ast.Bad, name.Name)
+	}
+	name.Obj = obj
+	return
+}
+
+// findField returns the object with the given name if visible in the type's scope.
+// If no such object is found, an error is reported and a bad object is returned instead.
+func (tc *typechecker) findField(typ *Type, name *ast.Ident) (obj *ast.Object) {
+	// TODO(gri) This is simplistic at the moment and ignores anonymous fields.
+	obj = typ.Scope.Lookup(name.Name)
+	if obj == nil {
+		tc.Errorf(name.Pos(), "%s not declared", name.Name)
+		obj = ast.NewObj(ast.Bad, name.Name)
+	}
+	return
+}
diff --git a/src/pkg/go/typechecker/testdata/test0.src b/src/pkg/go/typechecker/testdata/test0.src
new file mode 100644
index 000000000..4e317f214
--- /dev/null
+++ b/src/pkg/go/typechecker/testdata/test0.src
@@ -0,0 +1,94 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// type declarations
+
+package P0
+
+type (
+	B bool
+	I int32
+	A [10]P
+	T struct {
+		x, y P
+	}
+	P *T
+	R *R
+	F func(A) I
+	Y interface {
+		f(A) I
+	}
+	S []P
+	M map[I]F
+	C chan<- I
+)
+
+type (
+	a/* ERROR "illegal cycle" */ a
+	a/* ERROR "already declared" */ int
+
+	b/* ERROR "illegal cycle" */ c
+	c d
+	d e
+	e b /* ERROR "not a type" */
+
+	t *t
+
+	U V
+	V W
+	W *U
+
+	P1 *S2
+	P2 P1
+
+	S1 struct {
+		a, b, c int
+		u, v, a/* ERROR "already declared" */ float
+	}
+	S2/* ERROR "illegal cycle" */ struct {
+		x S2
+	}
+
+	L1 []L1
+	L2 []int
+
+	A1 [10]int
+	A2/* ERROR "illegal cycle" */ [10]A2
+	A3/* ERROR "illegal cycle" */ [10]struct {
+		x A4
+	}
+	A4 [10]A3
+
+	F1 func()
+	F2 func(x, y, z float)
+	F3 func(x, y, x /* ERROR "already declared" */ float)
+	F4 func() (x, y, x /* ERROR "already declared" */ float)
+	F5 func(x int) (x /* ERROR "already declared" */ float)
+
+	I1 interface{}
+	I2 interface {
+		m1()
+	}
+	I3 interface {
+		m1()
+		m1 /* ERROR "already declared" */ ()
+	}
+	I4 interface {
+		m1(x, y, x /* ERROR "already declared" */ float)
+		m2() (x, y, x /* ERROR "already declared" */ float)
+		m3(x int) (x /* ERROR "already declared" */ float)
+	}
+	I5 interface {
+		m1(I5)
+	}
+
+	C1 chan int
+	C2 <-chan int
+	C3 chan<- C3
+
+	M1 map[Last]string
+	M2 map[string]M2
+
+	Last int
+)
diff --git a/src/pkg/go/typechecker/testdata/test1.src b/src/pkg/go/typechecker/testdata/test1.src
new file mode 100644
index 000000000..b5531fb9f
--- /dev/null
+++ b/src/pkg/go/typechecker/testdata/test1.src
@@ -0,0 +1,13 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// const and var declarations
+
+package P1
+
+const (
+	c1 = 0
+	c2     int = 0
+	c3, c4 = 0
+)
diff --git a/src/pkg/go/typechecker/testdata/test3.src b/src/pkg/go/typechecker/testdata/test3.src
new file mode 100644
index 000000000..2e1a9fa8f
--- /dev/null
+++ b/src/pkg/go/typechecker/testdata/test3.src
@@ -0,0 +1,41 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package P3
+
+// function and method signatures
+
+func _()                                        {}
+func _()                                        {}
+func _(x, x /* ERROR "already declared" */ int) {}
+
+func f()                                 {}
+func f /* ERROR "already declared" */ () {}
+
+func (*foo /* ERROR "invalid receiver" */ ) m() {}
+func (bar /* ERROR "not a type" */ ) m()        {}
+
+func f1(x, _, _ int) (_, _ float)                              {}
+func f2(x, y, x /* ERROR "already declared" */ int)            {}
+func f3(x, y int) (a, b, x /* ERROR "already declared" */ int) {}
+
+func (x *T) m1()                                 {}
+func (x *T) m1 /* ERROR "already declared" */ () {}
+func (x T) m1 /* ERROR "already declared" */ ()  {}
+func (T) m1 /* ERROR "already declared" */ ()    {}
+
+func (x *T) m2(u, x /* ERROR "already declared" */ int)               {}
+func (x *T) m3(a, b, c int) (u, x /* ERROR "already declared" */ int) {}
+// The following are disabled for now because the typechecker
+// in in the process of being rewritten and cannot handle them
+// at the moment
+//func (T) _(x, x /* "already declared" */ int)                   {}
+//func (T) _() (x, x /* "already declared" */ int)                {}
+
+//func (PT) _() {}
+
+var bar int
+
+type T struct{}
+type PT (T)
diff --git a/src/pkg/go/typechecker/testdata/test4.src b/src/pkg/go/typechecker/testdata/test4.src
new file mode 100644
index 000000000..94d3558f9
--- /dev/null
+++ b/src/pkg/go/typechecker/testdata/test4.src
@@ -0,0 +1,11 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Constant declarations
+
+package P4
+
+const (
+	c0 = 0
+)
diff --git a/src/pkg/go/typechecker/type.go b/src/pkg/go/typechecker/type.go
new file mode 100644
index 000000000..1b88eb54b
--- /dev/null
+++ b/src/pkg/go/typechecker/type.go
@@ -0,0 +1,118 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typechecker
+
+import "go/ast"
+
+// A Type represents a Go type.
+type Type struct {
+	Form     Form
+	Obj      *ast.Object // corresponding type name, or nil
+	Scope    *ast.Scope  // fields and methods, always present
+	N        uint        // basic type id, array length, number of function results, or channel direction
+	Key, Elt *Type       // map key and array, pointer, slice, map or channel element
+	Params   *ast.Scope  // function (receiver, input and result) parameters, tuple expressions (results of function calls), or nil
+	Expr     ast.Expr    // corresponding AST expression
+}
+
+// NewType creates a new type of a given form.
+func NewType(form Form) *Type {
+	return &Type{Form: form, Scope: ast.NewScope(nil)}
+}
+
+// Form describes the form of a type.
+type Form int
+
+// The list of possible type forms.
+const (
+	BadType    Form = iota // for error handling
+	Unresolved             // type not fully setup
+	Basic
+	Array
+	Struct
+	Pointer
+	Function
+	Method
+	Interface
+	Slice
+	Map
+	Channel
+	Tuple
+)
+
+var formStrings = [...]string{
+	BadType:    "badType",
+	Unresolved: "unresolved",
+	Basic:      "basic",
+	Array:      "array",
+	Struct:     "struct",
+	Pointer:    "pointer",
+	Function:   "function",
+	Method:     "method",
+	Interface:  "interface",
+	Slice:      "slice",
+	Map:        "map",
+	Channel:    "channel",
+	Tuple:      "tuple",
+}
+
+func (form Form) String() string { return formStrings[form] }
+
+// The list of basic type id's.
+const (
+	Bool = iota
+	Byte
+	Uint
+	Int
+	Float
+	Complex
+	Uintptr
+	String
+
+	Uint8
+	Uint16
+	Uint32
+	Uint64
+
+	Int8
+	Int16
+	Int32
+	Int64
+
+	Float32
+	Float64
+
+	Complex64
+	Complex128
+
+	// TODO(gri) ideal types are missing
+)
+
+var BasicTypes = map[uint]string{
+	Bool:    "bool",
+	Byte:    "byte",
+	Uint:    "uint",
+	Int:     "int",
+	Float:   "float",
+	Complex: "complex",
+	Uintptr: "uintptr",
+	String:  "string",
+
+	Uint8:  "uint8",
+	Uint16: "uint16",
+	Uint32: "uint32",
+	Uint64: "uint64",
+
+	Int8:  "int8",
+	Int16: "int16",
+	Int32: "int32",
+	Int64: "int64",
+
+	Float32: "float32",
+	Float64: "float64",
+
+	Complex64:  "complex64",
+	Complex128: "complex128",
+}
diff --git a/src/pkg/go/typechecker/typechecker.go b/src/pkg/go/typechecker/typechecker.go
new file mode 100644
index 000000000..24480165b
--- /dev/null
+++ b/src/pkg/go/typechecker/typechecker.go
@@ -0,0 +1,468 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// DEPRECATED PACKAGE - SEE go/types INSTEAD.
+// This package implements typechecking of a Go AST.
+// The result of the typecheck is an augmented AST
+// with object and type information for each identifier.
+//
+package typechecker
+
+import (
+	"fmt"
+	"go/ast"
+	"go/token"
+	"go/scanner"
+	"os"
+)
+
+// TODO(gri) don't report errors for objects/types that are marked as bad.
+
+
+const debug = true // set for debugging output
+
+// An importer takes an import path and returns the data describing the
+// respective package's exported interface. The data format is TBD.
+//
+type Importer func(path string) ([]byte, os.Error)
+
+// CheckPackage typechecks a package and augments the AST by setting
+// *ast.Object, *ast.Type, and *ast.Scope fields accordingly. If an
+// importer is provided, it is used to handle imports, otherwise they
+// are ignored (likely leading to typechecking errors).
+//
+// If errors are reported, the AST may be incompletely augmented (fields
+// may be nil) or contain incomplete object, type, or scope information.
+//
+func CheckPackage(fset *token.FileSet, pkg *ast.Package, importer Importer) os.Error {
+	var tc typechecker
+	tc.fset = fset
+	tc.importer = importer
+	tc.checkPackage(pkg)
+	return tc.GetError(scanner.Sorted)
+}
+
+// CheckFile typechecks a single file, but otherwise behaves like
+// CheckPackage. If the complete package consists of more than just
+// one file, the file may not typecheck without errors.
+//
+func CheckFile(fset *token.FileSet, file *ast.File, importer Importer) os.Error {
+	// create a single-file dummy package
+	pkg := &ast.Package{file.Name.Name, nil, nil, map[string]*ast.File{fset.Position(file.Name.NamePos).Filename: file}}
+	return CheckPackage(fset, pkg, importer)
+}
+
+// ----------------------------------------------------------------------------
+// Typechecker state
+
+type typechecker struct {
+	fset *token.FileSet
+	scanner.ErrorVector
+	importer Importer
+	globals  []*ast.Object        // list of global objects
+	topScope *ast.Scope           // current top-most scope
+	cyclemap map[*ast.Object]bool // for cycle detection
+	iota     int                  // current value of iota
+}
+
+func (tc *typechecker) Errorf(pos token.Pos, format string, args ...interface{}) {
+	tc.Error(tc.fset.Position(pos), fmt.Sprintf(format, args...))
+}
+
+func assert(pred bool) {
+	if !pred {
+		panic("internal error")
+	}
+}
+
+/*
+Typechecking is done in several phases:
+
+phase 1: declare all global objects; also collect all function and method declarations
+	- all objects have kind, name, decl fields; the decl field permits
+	  quick lookup of an object's declaration
+	- constant objects have an iota value
+	- type objects have unresolved types with empty scopes, all others have nil types
+	- report global double declarations
+
+phase 2: bind methods to their receiver base types
+	- receiver base types must be declared in the package, thus for
+	  each method a corresponding (unresolved) type must exist
+	- report method double declarations and errors with base types
+
+phase 3: resolve all global objects
+	- sequentially iterate through all objects in the global scope
+	- resolve types for all unresolved types and assign types to
+	  all attached methods
+	- assign types to all other objects, possibly by evaluating
+	  constant and initializer expressions
+	- resolution may recurse; a cyclemap is used to detect cycles
+	- report global typing errors
+
+phase 4: sequentially typecheck function and method bodies
+	- all global objects are declared and have types and values;
+	  all methods have types
+	- sequentially process statements in each body; any object
+	  referred to must be fully defined at this point
+	- report local typing errors
+*/
+
+func (tc *typechecker) checkPackage(pkg *ast.Package) {
+	// setup package scope
+	tc.topScope = Universe
+	tc.openScope()
+	defer tc.closeScope()
+
+	// TODO(gri) there's no file scope at the moment since we ignore imports
+
+	// phase 1: declare all global objects; also collect all function and method declarations
+	var funcs []*ast.FuncDecl
+	for _, file := range pkg.Files {
+		for _, decl := range file.Decls {
+			tc.declGlobal(decl)
+			if f, isFunc := decl.(*ast.FuncDecl); isFunc {
+				funcs = append(funcs, f)
+			}
+		}
+	}
+
+	// phase 2: bind methods to their receiver base types
+	for _, m := range funcs {
+		if m.Recv != nil {
+			tc.bindMethod(m)
+		}
+	}
+
+	// phase 3: resolve all global objects
+	tc.cyclemap = make(map[*ast.Object]bool)
+	for _, obj := range tc.globals {
+		tc.resolve(obj)
+	}
+	assert(len(tc.cyclemap) == 0)
+
+	// 4: sequentially typecheck function and method bodies
+	for _, f := range funcs {
+		ftype, _ := f.Name.Obj.Type.(*Type)
+		tc.checkBlock(f.Body.List, ftype)
+	}
+
+	pkg.Scope = tc.topScope
+}
+
+func (tc *typechecker) declGlobal(global ast.Decl) {
+	switch d := global.(type) {
+	case *ast.BadDecl:
+		// ignore
+
+	case *ast.GenDecl:
+		iota := 0
+		var prev *ast.ValueSpec
+		for _, spec := range d.Specs {
+			switch s := spec.(type) {
+			case *ast.ImportSpec:
+				// TODO(gri) imports go into file scope
+			case *ast.ValueSpec:
+				switch d.Tok {
+				case token.CONST:
+					if s.Values == nil {
+						// create a new spec with type and values from the previous one
+						if prev != nil {
+							s = &ast.ValueSpec{s.Doc, s.Names, prev.Type, prev.Values, s.Comment}
+						} else {
+							// TODO(gri) this should probably go into the const decl code
+							tc.Errorf(s.Pos(), "missing initializer for const %s", s.Names[0].Name)
+						}
+					}
+					for _, name := range s.Names {
+						tc.globals = append(tc.globals, tc.decl(ast.Con, name, s, iota))
+					}
+				case token.VAR:
+					for _, name := range s.Names {
+						tc.globals = append(tc.globals, tc.decl(ast.Var, name, s, 0))
+					}
+				default:
+					panic("unreachable")
+				}
+				prev = s
+				iota++
+			case *ast.TypeSpec:
+				obj := tc.decl(ast.Typ, s.Name, s, 0)
+				tc.globals = append(tc.globals, obj)
+				// give all type objects an unresolved type so
+				// that we can collect methods in the type scope
+				typ := NewType(Unresolved)
+				obj.Type = typ
+				typ.Obj = obj
+			default:
+				panic("unreachable")
+			}
+		}
+
+	case *ast.FuncDecl:
+		if d.Recv == nil {
+			tc.globals = append(tc.globals, tc.decl(ast.Fun, d.Name, d, 0))
+		}
+
+	default:
+		panic("unreachable")
+	}
+}
+
+// If x is of the form *T, deref returns T, otherwise it returns x.
+func deref(x ast.Expr) ast.Expr {
+	if p, isPtr := x.(*ast.StarExpr); isPtr {
+		x = p.X
+	}
+	return x
+}
+
+func (tc *typechecker) bindMethod(method *ast.FuncDecl) {
+	// a method is declared in the receiver base type's scope
+	var scope *ast.Scope
+	base := deref(method.Recv.List[0].Type)
+	if name, isIdent := base.(*ast.Ident); isIdent {
+		// if base is not an *ast.Ident, we had a syntax
+		// error and the parser reported an error already
+		obj := tc.topScope.Lookup(name.Name)
+		if obj == nil {
+			tc.Errorf(name.Pos(), "invalid receiver: %s is not declared in this package", name.Name)
+		} else if obj.Kind != ast.Typ {
+			tc.Errorf(name.Pos(), "invalid receiver: %s is not a type", name.Name)
+		} else {
+			typ := obj.Type.(*Type)
+			assert(typ.Form == Unresolved)
+			scope = typ.Scope
+		}
+	}
+	if scope == nil {
+		// no receiver type found; use a dummy scope
+		// (we still want to type-check the method
+		// body, so make sure there is a name object
+		// and type)
+		// TODO(gri) should we record the scope so
+		// that we don't lose the receiver for type-
+		// checking of the method body?
+		scope = ast.NewScope(nil)
+	}
+	tc.declInScope(scope, ast.Fun, method.Name, method, 0)
+}
+
+func (tc *typechecker) resolve(obj *ast.Object) {
+	// check for declaration cycles
+	if tc.cyclemap[obj] {
+		tc.Errorf(obj.Pos(), "illegal cycle in declaration of %s", obj.Name)
+		obj.Kind = ast.Bad
+		return
+	}
+	tc.cyclemap[obj] = true
+	defer func() {
+		tc.cyclemap[obj] = false, false
+	}()
+
+	// resolve non-type objects
+	typ, _ := obj.Type.(*Type)
+	if typ == nil {
+		switch obj.Kind {
+		case ast.Bad:
+			// ignore
+
+		case ast.Con:
+			tc.declConst(obj)
+
+		case ast.Var:
+			tc.declVar(obj)
+			obj.Type = tc.typeFor(nil, obj.Decl.(*ast.ValueSpec).Type, false)
+
+		case ast.Fun:
+			obj.Type = NewType(Function)
+			t := obj.Decl.(*ast.FuncDecl).Type
+			tc.declSignature(obj.Type.(*Type), nil, t.Params, t.Results)
+
+		default:
+			// type objects have non-nil types when resolve is called
+			if debug {
+				fmt.Printf("kind = %s\n", obj.Kind)
+			}
+			panic("unreachable")
+		}
+		return
+	}
+
+	// resolve type objects
+	if typ.Form == Unresolved {
+		tc.typeFor(typ, typ.Obj.Decl.(*ast.TypeSpec).Type, false)
+
+		// provide types for all methods
+		for _, obj := range typ.Scope.Objects {
+			if obj.Kind == ast.Fun {
+				assert(obj.Type == nil)
+				obj.Type = NewType(Method)
+				f := obj.Decl.(*ast.FuncDecl)
+				t := f.Type
+				tc.declSignature(obj.Type.(*Type), f.Recv, t.Params, t.Results)
+			}
+		}
+	}
+}
+
+func (tc *typechecker) checkBlock(body []ast.Stmt, ftype *Type) {
+	tc.openScope()
+	defer tc.closeScope()
+
+	// inject function/method parameters into block scope, if any
+	if ftype != nil {
+		for _, par := range ftype.Params.Objects {
+			if par.Name != "_" {
+				alt := tc.topScope.Insert(par)
+				assert(alt == nil) // ftype has no double declarations
+			}
+		}
+	}
+
+	for _, stmt := range body {
+		tc.checkStmt(stmt)
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Types
+
+// unparen removes parentheses around x, if any.
+func unparen(x ast.Expr) ast.Expr {
+	if ux, hasParens := x.(*ast.ParenExpr); hasParens {
+		return unparen(ux.X)
+	}
+	return x
+}
+
+func (tc *typechecker) declFields(scope *ast.Scope, fields *ast.FieldList, ref bool) (n uint) {
+	if fields != nil {
+		for _, f := range fields.List {
+			typ := tc.typeFor(nil, f.Type, ref)
+			for _, name := range f.Names {
+				fld := tc.declInScope(scope, ast.Var, name, f, 0)
+				fld.Type = typ
+				n++
+			}
+		}
+	}
+	return n
+}
+
+func (tc *typechecker) declSignature(typ *Type, recv, params, results *ast.FieldList) {
+	assert((typ.Form == Method) == (recv != nil))
+	typ.Params = ast.NewScope(nil)
+	tc.declFields(typ.Params, recv, true)
+	tc.declFields(typ.Params, params, true)
+	typ.N = tc.declFields(typ.Params, results, true)
+}
+
+func (tc *typechecker) typeFor(def *Type, x ast.Expr, ref bool) (typ *Type) {
+	x = unparen(x)
+
+	// type name
+	if t, isIdent := x.(*ast.Ident); isIdent {
+		obj := tc.find(t)
+
+		if obj.Kind != ast.Typ {
+			tc.Errorf(t.Pos(), "%s is not a type", t.Name)
+			if def == nil {
+				typ = NewType(BadType)
+			} else {
+				typ = def
+				typ.Form = BadType
+			}
+			typ.Expr = x
+			return
+		}
+
+		if !ref {
+			tc.resolve(obj) // check for cycles even if type resolved
+		}
+		typ = obj.Type.(*Type)
+
+		if def != nil {
+			// new type declaration: copy type structure
+			def.Form = typ.Form
+			def.N = typ.N
+			def.Key, def.Elt = typ.Key, typ.Elt
+			def.Params = typ.Params
+			def.Expr = x
+			typ = def
+		}
+		return
+	}
+
+	// type literal
+	typ = def
+	if typ == nil {
+		typ = NewType(BadType)
+	}
+	typ.Expr = x
+
+	switch t := x.(type) {
+	case *ast.SelectorExpr:
+		if debug {
+			fmt.Println("qualified identifier unimplemented")
+		}
+		typ.Form = BadType
+
+	case *ast.StarExpr:
+		typ.Form = Pointer
+		typ.Elt = tc.typeFor(nil, t.X, true)
+
+	case *ast.ArrayType:
+		if t.Len != nil {
+			typ.Form = Array
+			// TODO(gri) compute the real length
+			// (this may call resolve recursively)
+			(*typ).N = 42
+		} else {
+			typ.Form = Slice
+		}
+		typ.Elt = tc.typeFor(nil, t.Elt, t.Len == nil)
+
+	case *ast.StructType:
+		typ.Form = Struct
+		tc.declFields(typ.Scope, t.Fields, false)
+
+	case *ast.FuncType:
+		typ.Form = Function
+		tc.declSignature(typ, nil, t.Params, t.Results)
+
+	case *ast.InterfaceType:
+		typ.Form = Interface
+		tc.declFields(typ.Scope, t.Methods, true)
+
+	case *ast.MapType:
+		typ.Form = Map
+		typ.Key = tc.typeFor(nil, t.Key, true)
+		typ.Elt = tc.typeFor(nil, t.Value, true)
+
+	case *ast.ChanType:
+		typ.Form = Channel
+		typ.N = uint(t.Dir)
+		typ.Elt = tc.typeFor(nil, t.Value, true)
+
+	default:
+		if debug {
+			fmt.Printf("x is %T\n", x)
+		}
+		panic("unreachable")
+	}
+
+	return
+}
+
+// ----------------------------------------------------------------------------
+// TODO(gri) implement these place holders
+
+func (tc *typechecker) declConst(*ast.Object) {
+}
+
+func (tc *typechecker) declVar(*ast.Object) {
+}
+
+func (tc *typechecker) checkStmt(ast.Stmt) {
+}
diff --git a/src/pkg/go/typechecker/typechecker_test.go b/src/pkg/go/typechecker/typechecker_test.go
new file mode 100644
index 000000000..4bad4499a
--- /dev/null
+++ b/src/pkg/go/typechecker/typechecker_test.go
@@ -0,0 +1,163 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements a simple typechecker test harness. Packages found
+// in the testDir directory are typechecked. Error messages reported by
+// the typechecker are compared against the error messages expected for
+// the test files.
+//
+// Expected errors are indicated in the test files by putting a comment
+// of the form /* ERROR "rx" */ immediately following an offending token.
+// The harness will verify that an error matching the regular expression
+// rx is reported at that source position. Consecutive comments may be
+// used to indicate multiple errors for the same token position.
+//
+// For instance, the following test file indicates that a "not declared"
+// error should be reported for the undeclared variable x:
+//
+//	package P0
+//	func f() {
+//		_ = x /* ERROR "not declared" */ + 1
+//	}
+// 
+// If the -pkg flag is set, only packages with package names matching
+// the regular expression provided via the flag value are tested.
+
+package typechecker
+
+import (
+	"flag"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/scanner"
+	"go/token"
+	"io/ioutil"
+	"os"
+	"regexp"
+	"sort"
+	"strings"
+	"testing"
+)
+
+const testDir = "./testdata" // location of test packages
+
+var fset = token.NewFileSet()
+
+var (
+	pkgPat = flag.String("pkg", ".*", "regular expression to select test packages by package name")
+	trace  = flag.Bool("trace", false, "print package names")
+)
+
+// ERROR comments must be of the form /* ERROR "rx" */ and rx is
+// a regular expression that matches the expected error message.
+var errRx = regexp.MustCompile(`^/\* *ERROR *"([^"]*)" *\*/$`)
+
+// expectedErrors collects the regular expressions of ERROR comments
+// found in the package files of pkg and returns them in sorted order
+// (by filename and position).
+func expectedErrors(t *testing.T, pkg *ast.Package) (list scanner.ErrorList) {
+	// scan all package files
+	for filename := range pkg.Files {
+		src, err := ioutil.ReadFile(filename)
+		if err != nil {
+			t.Fatalf("expectedErrors(%s): %v", pkg.Name, err)
+		}
+
+		var s scanner.Scanner
+		file := fset.AddFile(filename, fset.Base(), len(src))
+		s.Init(file, src, nil, scanner.ScanComments)
+		var prev token.Pos // position of last non-comment token
+	loop:
+		for {
+			pos, tok, lit := s.Scan()
+			switch tok {
+			case token.EOF:
+				break loop
+			case token.COMMENT:
+				s := errRx.FindStringSubmatch(lit)
+				if len(s) == 2 {
+					list = append(list, &scanner.Error{fset.Position(prev), string(s[1])})
+				}
+			default:
+				prev = pos
+			}
+		}
+	}
+	sort.Sort(list) // multiple files may not be sorted
+	return
+}
+
+func testFilter(f *os.FileInfo) bool {
+	return strings.HasSuffix(f.Name, ".src") && f.Name[0] != '.'
+}
+
+func checkError(t *testing.T, expected, found *scanner.Error) {
+	rx, err := regexp.Compile(expected.Msg)
+	if err != nil {
+		t.Errorf("%s: %v", expected.Pos, err)
+		return
+	}
+
+	match := rx.MatchString(found.Msg)
+
+	if expected.Pos.Offset != found.Pos.Offset {
+		if match {
+			t.Errorf("%s: expected error should have been at %s", expected.Pos, found.Pos)
+		} else {
+			t.Errorf("%s: error matching %q expected", expected.Pos, expected.Msg)
+			return
+		}
+	}
+
+	if !match {
+		t.Errorf("%s: %q does not match %q", expected.Pos, expected.Msg, found.Msg)
+	}
+}
+
+func TestTypeCheck(t *testing.T) {
+	flag.Parse()
+	pkgRx, err := regexp.Compile(*pkgPat)
+	if err != nil {
+		t.Fatalf("illegal flag value %q: %s", *pkgPat, err)
+	}
+
+	pkgs, err := parser.ParseDir(fset, testDir, testFilter, 0)
+	if err != nil {
+		scanner.PrintError(os.Stderr, err)
+		t.Fatalf("packages in %s contain syntax errors", testDir)
+	}
+
+	for _, pkg := range pkgs {
+		if !pkgRx.MatchString(pkg.Name) {
+			continue // only test selected packages
+		}
+
+		if *trace {
+			fmt.Println(pkg.Name)
+		}
+
+		xlist := expectedErrors(t, pkg)
+		err := CheckPackage(fset, pkg, nil)
+		if err != nil {
+			if elist, ok := err.(scanner.ErrorList); ok {
+				// verify that errors match
+				for i := 0; i < len(xlist) && i < len(elist); i++ {
+					checkError(t, xlist[i], elist[i])
+				}
+				// the correct number or errors must have been found
+				if len(xlist) != len(elist) {
+					fmt.Fprintf(os.Stderr, "%s\n", pkg.Name)
+					scanner.PrintError(os.Stderr, elist)
+					fmt.Fprintln(os.Stderr)
+					t.Errorf("TypeCheck(%s): %d errors expected but %d reported", pkg.Name, len(xlist), len(elist))
+				}
+			} else {
+				t.Errorf("TypeCheck(%s): %v", pkg.Name, err)
+			}
+		} else if len(xlist) > 0 {
+			t.Errorf("TypeCheck(%s): %d errors expected but 0 reported", pkg.Name, len(xlist))
+		}
+	}
+}
diff --git a/src/pkg/go/typechecker/universe.go b/src/pkg/go/typechecker/universe.go
new file mode 100644
index 000000000..81c14a05e
--- /dev/null
+++ b/src/pkg/go/typechecker/universe.go
@@ -0,0 +1,36 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package typechecker
+
+import "go/ast"
+
+// TODO(gri) should this be in package ast?
+
+// The Universe scope contains all predeclared identifiers.
+var Universe *ast.Scope
+
+func def(obj *ast.Object) {
+	alt := Universe.Insert(obj)
+	if alt != nil {
+		panic("object declared twice")
+	}
+}
+
+func init() {
+	Universe = ast.NewScope(nil)
+
+	// basic types
+	for n, name := range BasicTypes {
+		typ := NewType(Basic)
+		typ.N = n
+		obj := ast.NewObj(ast.Typ, name)
+		obj.Type = typ
+		typ.Obj = obj
+		def(obj)
+	}
+
+	// built-in functions
+	// TODO(gri) implement this
+}
diff --git a/src/pkg/go/types/Makefile b/src/pkg/go/types/Makefile
new file mode 100644
index 000000000..4ca707c73
--- /dev/null
+++ b/src/pkg/go/types/Makefile
@@ -0,0 +1,16 @@
+# Copyright 2010 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+
+include ../../../Make.inc
+
+TARG=go/types
+GOFILES=\
+	check.go\
+	const.go\
+	exportdata.go\
+	gcimporter.go\
+	types.go\
+	universe.go\
+
+include ../../../Make.pkg
diff --git a/src/pkg/go/types/check.go b/src/pkg/go/types/check.go
new file mode 100644
index 000000000..87e3e93da
--- /dev/null
+++ b/src/pkg/go/types/check.go
@@ -0,0 +1,226 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements the Check function, which typechecks a package.
+
+package types
+
+import (
+	"fmt"
+	"go/ast"
+	"go/scanner"
+	"go/token"
+	"os"
+	"strconv"
+)
+
+const debug = false
+
+type checker struct {
+	fset *token.FileSet
+	scanner.ErrorVector
+	types map[ast.Expr]Type
+}
+
+func (c *checker) errorf(pos token.Pos, format string, args ...interface{}) string {
+	msg := fmt.Sprintf(format, args...)
+	c.Error(c.fset.Position(pos), msg)
+	return msg
+}
+
+// collectFields collects struct fields tok = token.STRUCT), interface methods
+// (tok = token.INTERFACE), and function arguments/results (tok = token.FUNC).
+func (c *checker) collectFields(tok token.Token, list *ast.FieldList, cycleOk bool) (fields ObjList, tags []string, isVariadic bool) {
+	if list != nil {
+		for _, field := range list.List {
+			ftype := field.Type
+			if t, ok := ftype.(*ast.Ellipsis); ok {
+				ftype = t.Elt
+				isVariadic = true
+			}
+			typ := c.makeType(ftype, cycleOk)
+			tag := ""
+			if field.Tag != nil {
+				assert(field.Tag.Kind == token.STRING)
+				tag, _ = strconv.Unquote(field.Tag.Value)
+			}
+			if len(field.Names) > 0 {
+				// named fields
+				for _, name := range field.Names {
+					obj := name.Obj
+					obj.Type = typ
+					fields = append(fields, obj)
+					if tok == token.STRUCT {
+						tags = append(tags, tag)
+					}
+				}
+			} else {
+				// anonymous field
+				switch tok {
+				case token.STRUCT:
+					tags = append(tags, tag)
+					fallthrough
+				case token.FUNC:
+					obj := ast.NewObj(ast.Var, "")
+					obj.Type = typ
+					fields = append(fields, obj)
+				case token.INTERFACE:
+					utyp := Underlying(typ)
+					if typ, ok := utyp.(*Interface); ok {
+						// TODO(gri) This is not good enough. Check for double declarations!
+						fields = append(fields, typ.Methods...)
+					} else if _, ok := utyp.(*Bad); !ok {
+						// if utyp is Bad, don't complain (the root cause was reported before)
+						c.errorf(ftype.Pos(), "interface contains embedded non-interface type")
+					}
+				default:
+					panic("unreachable")
+				}
+			}
+		}
+	}
+	return
+}
+
+// makeType makes a new type for an AST type specification x or returns
+// the type referred to by a type name x. If cycleOk is set, a type may
+// refer to itself directly or indirectly; otherwise cycles are errors.
+//
+func (c *checker) makeType(x ast.Expr, cycleOk bool) (typ Type) {
+	if debug {
+		fmt.Printf("makeType (cycleOk = %v)\n", cycleOk)
+		ast.Print(c.fset, x)
+		defer func() {
+			fmt.Printf("-> %T %v\n\n", typ, typ)
+		}()
+	}
+
+	switch t := x.(type) {
+	case *ast.BadExpr:
+		return &Bad{}
+
+	case *ast.Ident:
+		// type name
+		obj := t.Obj
+		if obj == nil {
+			// unresolved identifier (error has been reported before)
+			return &Bad{Msg: "unresolved identifier"}
+		}
+		if obj.Kind != ast.Typ {
+			msg := c.errorf(t.Pos(), "%s is not a type", t.Name)
+			return &Bad{Msg: msg}
+		}
+		c.checkObj(obj, cycleOk)
+		if !cycleOk && obj.Type.(*Name).Underlying == nil {
+			// TODO(gri) Enable this message again once its position
+			// is independent of the underlying map implementation.
+			// msg := c.errorf(obj.Pos(), "illegal cycle in declaration of %s", obj.Name)
+			msg := "illegal cycle"
+			return &Bad{Msg: msg}
+		}
+		return obj.Type.(Type)
+
+	case *ast.ParenExpr:
+		return c.makeType(t.X, cycleOk)
+
+	case *ast.SelectorExpr:
+		// qualified identifier
+		// TODO (gri) eventually, this code belongs to expression
+		//            type checking - here for the time being
+		if ident, ok := t.X.(*ast.Ident); ok {
+			if obj := ident.Obj; obj != nil {
+				if obj.Kind != ast.Pkg {
+					msg := c.errorf(ident.Pos(), "%s is not a package", obj.Name)
+					return &Bad{Msg: msg}
+				}
+				// TODO(gri) we have a package name but don't
+				// have the mapping from package name to package
+				// scope anymore (created in ast.NewPackage).
+				return &Bad{} // for now
+			}
+		}
+		// TODO(gri) can this really happen (the parser should have excluded this)?
+		msg := c.errorf(t.Pos(), "expected qualified identifier")
+		return &Bad{Msg: msg}
+
+	case *ast.StarExpr:
+		return &Pointer{Base: c.makeType(t.X, true)}
+
+	case *ast.ArrayType:
+		if t.Len != nil {
+			// TODO(gri) compute length
+			return &Array{Elt: c.makeType(t.Elt, cycleOk)}
+		}
+		return &Slice{Elt: c.makeType(t.Elt, true)}
+
+	case *ast.StructType:
+		fields, tags, _ := c.collectFields(token.STRUCT, t.Fields, cycleOk)
+		return &Struct{Fields: fields, Tags: tags}
+
+	case *ast.FuncType:
+		params, _, _ := c.collectFields(token.FUNC, t.Params, true)
+		results, _, isVariadic := c.collectFields(token.FUNC, t.Results, true)
+		return &Func{Recv: nil, Params: params, Results: results, IsVariadic: isVariadic}
+
+	case *ast.InterfaceType:
+		methods, _, _ := c.collectFields(token.INTERFACE, t.Methods, cycleOk)
+		methods.Sort()
+		return &Interface{Methods: methods}
+
+	case *ast.MapType:
+		return &Map{Key: c.makeType(t.Key, true), Elt: c.makeType(t.Key, true)}
+
+	case *ast.ChanType:
+		return &Chan{Dir: t.Dir, Elt: c.makeType(t.Value, true)}
+	}
+
+	panic(fmt.Sprintf("unreachable (%T)", x))
+}
+
+// checkObj type checks an object.
+func (c *checker) checkObj(obj *ast.Object, ref bool) {
+	if obj.Type != nil {
+		// object has already been type checked
+		return
+	}
+
+	switch obj.Kind {
+	case ast.Bad:
+		// ignore
+
+	case ast.Con:
+		// TODO(gri) complete this
+
+	case ast.Typ:
+		typ := &Name{Obj: obj}
+		obj.Type = typ // "mark" object so recursion terminates
+		typ.Underlying = Underlying(c.makeType(obj.Decl.(*ast.TypeSpec).Type, ref))
+
+	case ast.Var:
+		// TODO(gri) complete this
+
+	case ast.Fun:
+		// TODO(gri) complete this
+
+	default:
+		panic("unreachable")
+	}
+}
+
+// Check typechecks a package.
+// It augments the AST by assigning types to all ast.Objects and returns a map
+// of types for all expression nodes in statements, and a scanner.ErrorList if
+// there are errors.
+//
+func Check(fset *token.FileSet, pkg *ast.Package) (types map[ast.Expr]Type, err os.Error) {
+	var c checker
+	c.fset = fset
+	c.types = make(map[ast.Expr]Type)
+
+	for _, obj := range pkg.Scope.Objects {
+		c.checkObj(obj, false)
+	}
+
+	return c.types, c.GetError(scanner.NoMultiples)
+}
diff --git a/src/pkg/go/types/check_test.go b/src/pkg/go/types/check_test.go
new file mode 100644
index 000000000..8be653fcb
--- /dev/null
+++ b/src/pkg/go/types/check_test.go
@@ -0,0 +1,215 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements a typechecker test harness. The packages specified
+// in tests are typechecked. Error messages reported by the typechecker are
+// compared against the error messages expected in the test files.
+//
+// Expected errors are indicated in the test files by putting a comment
+// of the form /* ERROR "rx" */ immediately following an offending token.
+// The harness will verify that an error matching the regular expression
+// rx is reported at that source position. Consecutive comments may be
+// used to indicate multiple errors for the same token position.
+//
+// For instance, the following test file indicates that a "not declared"
+// error should be reported for the undeclared variable x:
+//
+//	package p
+//	func f() {
+//		_ = x /* ERROR "not declared" */ + 1
+//	}
+
+package types
+
+import (
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/scanner"
+	"go/token"
+	"io/ioutil"
+	"os"
+	"regexp"
+	"testing"
+)
+
+// The test filenames do not end in .go so that they are invisible
+// to gofmt since they contain comments that must not change their
+// positions relative to surrounding tokens.
+
+var tests = []struct {
+	name  string
+	files []string
+}{
+	{"test0", []string{"testdata/test0.src"}},
+}
+
+var fset = token.NewFileSet()
+
+// TODO(gri) This functionality should be in token.Fileset.
+func getFile(filename string) *token.File {
+	for f := range fset.Files() {
+		if f.Name() == filename {
+			return f
+		}
+	}
+	return nil
+}
+
+// TODO(gri) This functionality should be in token.Fileset.
+func getPos(filename string, offset int) token.Pos {
+	if f := getFile(filename); f != nil {
+		return f.Pos(offset)
+	}
+	return token.NoPos
+}
+
+// TODO(gri) Need to revisit parser interface. We should be able to use parser.ParseFiles
+//           or a similar function instead.
+func parseFiles(t *testing.T, testname string, filenames []string) (map[string]*ast.File, os.Error) {
+	files := make(map[string]*ast.File)
+	var errors scanner.ErrorList
+	for _, filename := range filenames {
+		if _, exists := files[filename]; exists {
+			t.Fatalf("%s: duplicate file %s", testname, filename)
+		}
+		file, err := parser.ParseFile(fset, filename, nil, parser.DeclarationErrors)
+		if file == nil {
+			t.Fatalf("%s: could not parse file %s", testname, filename)
+		}
+		files[filename] = file
+		if err != nil {
+			// if the parser returns a non-scanner.ErrorList error
+			// the file couldn't be read in the first place and
+			// file == nil; in that case we shouldn't reach here
+			errors = append(errors, err.(scanner.ErrorList)...)
+		}
+
+	}
+	return files, errors
+}
+
+// ERROR comments must be of the form /* ERROR "rx" */ and rx is
+// a regular expression that matches the expected error message.
+//
+var errRx = regexp.MustCompile(`^/\* *ERROR *"([^"]*)" *\*/$`)
+
+// expectedErrors collects the regular expressions of ERROR comments found
+// in files and returns them as a map of error positions to error messages.
+//
+func expectedErrors(t *testing.T, testname string, files map[string]*ast.File) map[token.Pos]string {
+	errors := make(map[token.Pos]string)
+	for filename := range files {
+		src, err := ioutil.ReadFile(filename)
+		if err != nil {
+			t.Fatalf("%s: could not read %s", testname, filename)
+		}
+
+		var s scanner.Scanner
+		// file was parsed already - do not add it again to the file
+		// set otherwise the position information returned here will
+		// not match the position information collected by the parser
+		s.Init(getFile(filename), src, nil, scanner.ScanComments)
+		var prev token.Pos // position of last non-comment token
+
+	scanFile:
+		for {
+			pos, tok, lit := s.Scan()
+			switch tok {
+			case token.EOF:
+				break scanFile
+			case token.COMMENT:
+				s := errRx.FindStringSubmatch(lit)
+				if len(s) == 2 {
+					errors[prev] = string(s[1])
+				}
+			default:
+				prev = pos
+			}
+		}
+	}
+	return errors
+}
+
+func eliminate(t *testing.T, expected map[token.Pos]string, errors os.Error) {
+	if errors == nil {
+		return
+	}
+	for _, error := range errors.(scanner.ErrorList) {
+		// error.Pos is a token.Position, but we want
+		// a token.Pos so we can do a map lookup
+		// TODO(gri) Need to move scanner.Errors over
+		//           to use token.Pos and file set info.
+		pos := getPos(error.Pos.Filename, error.Pos.Offset)
+		if msg, found := expected[pos]; found {
+			// we expect a message at pos; check if it matches
+			rx, err := regexp.Compile(msg)
+			if err != nil {
+				t.Errorf("%s: %v", error.Pos, err)
+				continue
+			}
+			if match := rx.MatchString(error.Msg); !match {
+				t.Errorf("%s: %q does not match %q", error.Pos, error.Msg, msg)
+				continue
+			}
+			// we have a match - eliminate this error
+			expected[pos] = "", false
+		} else {
+			// To keep in mind when analyzing failed test output:
+			// If the same error position occurs multiple times in errors,
+			// this message will be triggered (because the first error at
+			// the position removes this position from the expected errors).
+			t.Errorf("%s: no (multiple?) error expected, but found: %s", error.Pos, error.Msg)
+		}
+	}
+}
+
+func check(t *testing.T, testname string, testfiles []string) {
+	// TODO(gri) Eventually all these different phases should be
+	//           subsumed into a single function call that takes
+	//           a set of files and creates a fully resolved and
+	//           type-checked AST.
+
+	files, err := parseFiles(t, testname, testfiles)
+
+	// we are expecting the following errors
+	// (collect these after parsing the files so that
+	// they are found in the file set)
+	errors := expectedErrors(t, testname, files)
+
+	// verify errors returned by the parser
+	eliminate(t, errors, err)
+
+	// verify errors returned after resolving identifiers
+	pkg, err := ast.NewPackage(fset, files, GcImporter, Universe)
+	eliminate(t, errors, err)
+
+	// verify errors returned by the typechecker
+	_, err = Check(fset, pkg)
+	eliminate(t, errors, err)
+
+	// there should be no expected errors left
+	if len(errors) > 0 {
+		t.Errorf("%s: %d errors not reported:", testname, len(errors))
+		for pos, msg := range errors {
+			t.Errorf("%s: %s\n", fset.Position(pos), msg)
+		}
+	}
+}
+
+func TestCheck(t *testing.T) {
+	// For easy debugging w/o changing the testing code,
+	// if there is a local test file, only test that file.
+	const testfile = "test.go"
+	if fi, err := os.Stat(testfile); err == nil && fi.IsRegular() {
+		fmt.Printf("WARNING: Testing only %s (remove it to run all tests)\n", testfile)
+		check(t, testfile, []string{testfile})
+		return
+	}
+
+	// Otherwise, run all the tests.
+	for _, test := range tests {
+		check(t, test.name, test.files)
+	}
+}
diff --git a/src/pkg/go/types/const.go b/src/pkg/go/types/const.go
new file mode 100644
index 000000000..1ef95d9f9
--- /dev/null
+++ b/src/pkg/go/types/const.go
@@ -0,0 +1,332 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements operations on ideal constants.
+
+package types
+
+import (
+	"big"
+	"go/token"
+	"strconv"
+)
+
+// TODO(gri) Consider changing the API so Const is an interface
+//           and operations on consts don't have to type switch.
+
+// A Const implements an ideal constant Value.
+// The zero value z for a Const is not a valid constant value.
+type Const struct {
+	// representation of constant values:
+	// ideal bool     ->  bool
+	// ideal int      ->  *big.Int
+	// ideal float    ->  *big.Rat
+	// ideal complex  ->  cmplx
+	// ideal string   ->  string
+	val interface{}
+}
+
+// Representation of complex values.
+type cmplx struct {
+	re, im *big.Rat
+}
+
+func assert(cond bool) {
+	if !cond {
+		panic("go/types internal error: assertion failed")
+	}
+}
+
+// MakeConst makes an ideal constant from a literal
+// token and the corresponding literal string.
+func MakeConst(tok token.Token, lit string) Const {
+	switch tok {
+	case token.INT:
+		var x big.Int
+		_, ok := x.SetString(lit, 0)
+		assert(ok)
+		return Const{&x}
+	case token.FLOAT:
+		var y big.Rat
+		_, ok := y.SetString(lit)
+		assert(ok)
+		return Const{&y}
+	case token.IMAG:
+		assert(lit[len(lit)-1] == 'i')
+		var im big.Rat
+		_, ok := im.SetString(lit[0 : len(lit)-1])
+		assert(ok)
+		return Const{cmplx{big.NewRat(0, 1), &im}}
+	case token.CHAR:
+		assert(lit[0] == '\'' && lit[len(lit)-1] == '\'')
+		code, _, _, err := strconv.UnquoteChar(lit[1:len(lit)-1], '\'')
+		assert(err == nil)
+		return Const{big.NewInt(int64(code))}
+	case token.STRING:
+		s, err := strconv.Unquote(lit)
+		assert(err == nil)
+		return Const{s}
+	}
+	panic("unreachable")
+}
+
+// MakeZero returns the zero constant for the given type.
+func MakeZero(typ *Type) Const {
+	// TODO(gri) fix this
+	return Const{0}
+}
+
+// Match attempts to match the internal constant representations of x and y.
+// If the attempt is successful, the result is the values of x and y,
+// if necessary converted to have the same internal representation; otherwise
+// the results are invalid.
+func (x Const) Match(y Const) (u, v Const) {
+	switch a := x.val.(type) {
+	case bool:
+		if _, ok := y.val.(bool); ok {
+			u, v = x, y
+		}
+	case *big.Int:
+		switch y.val.(type) {
+		case *big.Int:
+			u, v = x, y
+		case *big.Rat:
+			var z big.Rat
+			z.SetInt(a)
+			u, v = Const{&z}, y
+		case cmplx:
+			var z big.Rat
+			z.SetInt(a)
+			u, v = Const{cmplx{&z, big.NewRat(0, 1)}}, y
+		}
+	case *big.Rat:
+		switch y.val.(type) {
+		case *big.Int:
+			v, u = y.Match(x)
+		case *big.Rat:
+			u, v = x, y
+		case cmplx:
+			u, v = Const{cmplx{a, big.NewRat(0, 0)}}, y
+		}
+	case cmplx:
+		switch y.val.(type) {
+		case *big.Int, *big.Rat:
+			v, u = y.Match(x)
+		case cmplx:
+			u, v = x, y
+		}
+	case string:
+		if _, ok := y.val.(string); ok {
+			u, v = x, y
+		}
+	default:
+		panic("unreachable")
+	}
+	return
+}
+
+// Convert attempts to convert the constant x to a given type.
+// If the attempt is successful, the result is the new constant;
+// otherwise the result is invalid.
+func (x Const) Convert(typ *Type) Const {
+	// TODO(gri) implement this
+	switch x := x.val.(type) {
+	case bool:
+	case *big.Int:
+	case *big.Rat:
+	case cmplx:
+	case string:
+	}
+	return x
+}
+
+func (x Const) String() string {
+	switch x := x.val.(type) {
+	case bool:
+		if x {
+			return "true"
+		}
+		return "false"
+	case *big.Int:
+		return x.String()
+	case *big.Rat:
+		return x.FloatString(10) // 10 digits of precision after decimal point seems fine
+	case cmplx:
+		// TODO(gri) don't print 0 components
+		return x.re.FloatString(10) + " + " + x.im.FloatString(10) + "i"
+	case string:
+		return x
+	}
+	panic("unreachable")
+}
+
+func (x Const) UnaryOp(op token.Token) Const {
+	panic("unimplemented")
+}
+
+func (x Const) BinaryOp(op token.Token, y Const) Const {
+	var z interface{}
+	switch x := x.val.(type) {
+	case bool:
+		z = binaryBoolOp(x, op, y.val.(bool))
+	case *big.Int:
+		z = binaryIntOp(x, op, y.val.(*big.Int))
+	case *big.Rat:
+		z = binaryFloatOp(x, op, y.val.(*big.Rat))
+	case cmplx:
+		z = binaryCmplxOp(x, op, y.val.(cmplx))
+	case string:
+		z = binaryStringOp(x, op, y.val.(string))
+	default:
+		panic("unreachable")
+	}
+	return Const{z}
+}
+
+func binaryBoolOp(x bool, op token.Token, y bool) interface{} {
+	switch op {
+	case token.EQL:
+		return x == y
+	case token.NEQ:
+		return x != y
+	}
+	panic("unreachable")
+}
+
+func binaryIntOp(x *big.Int, op token.Token, y *big.Int) interface{} {
+	var z big.Int
+	switch op {
+	case token.ADD:
+		return z.Add(x, y)
+	case token.SUB:
+		return z.Sub(x, y)
+	case token.MUL:
+		return z.Mul(x, y)
+	case token.QUO:
+		return z.Quo(x, y)
+	case token.REM:
+		return z.Rem(x, y)
+	case token.AND:
+		return z.And(x, y)
+	case token.OR:
+		return z.Or(x, y)
+	case token.XOR:
+		return z.Xor(x, y)
+	case token.AND_NOT:
+		return z.AndNot(x, y)
+	case token.SHL:
+		panic("unimplemented")
+	case token.SHR:
+		panic("unimplemented")
+	case token.EQL:
+		return x.Cmp(y) == 0
+	case token.NEQ:
+		return x.Cmp(y) != 0
+	case token.LSS:
+		return x.Cmp(y) < 0
+	case token.LEQ:
+		return x.Cmp(y) <= 0
+	case token.GTR:
+		return x.Cmp(y) > 0
+	case token.GEQ:
+		return x.Cmp(y) >= 0
+	}
+	panic("unreachable")
+}
+
+func binaryFloatOp(x *big.Rat, op token.Token, y *big.Rat) interface{} {
+	var z big.Rat
+	switch op {
+	case token.ADD:
+		return z.Add(x, y)
+	case token.SUB:
+		return z.Sub(x, y)
+	case token.MUL:
+		return z.Mul(x, y)
+	case token.QUO:
+		return z.Quo(x, y)
+	case token.EQL:
+		return x.Cmp(y) == 0
+	case token.NEQ:
+		return x.Cmp(y) != 0
+	case token.LSS:
+		return x.Cmp(y) < 0
+	case token.LEQ:
+		return x.Cmp(y) <= 0
+	case token.GTR:
+		return x.Cmp(y) > 0
+	case token.GEQ:
+		return x.Cmp(y) >= 0
+	}
+	panic("unreachable")
+}
+
+func binaryCmplxOp(x cmplx, op token.Token, y cmplx) interface{} {
+	a, b := x.re, x.im
+	c, d := y.re, y.im
+	switch op {
+	case token.ADD:
+		// (a+c) + i(b+d)
+		var re, im big.Rat
+		re.Add(a, c)
+		im.Add(b, d)
+		return cmplx{&re, &im}
+	case token.SUB:
+		// (a-c) + i(b-d)
+		var re, im big.Rat
+		re.Sub(a, c)
+		im.Sub(b, d)
+		return cmplx{&re, &im}
+	case token.MUL:
+		// (ac-bd) + i(bc+ad)
+		var ac, bd, bc, ad big.Rat
+		ac.Mul(a, c)
+		bd.Mul(b, d)
+		bc.Mul(b, c)
+		ad.Mul(a, d)
+		var re, im big.Rat
+		re.Sub(&ac, &bd)
+		im.Add(&bc, &ad)
+		return cmplx{&re, &im}
+	case token.QUO:
+		// (ac+bd)/s + i(bc-ad)/s, with s = cc + dd
+		var ac, bd, bc, ad, s big.Rat
+		ac.Mul(a, c)
+		bd.Mul(b, d)
+		bc.Mul(b, c)
+		ad.Mul(a, d)
+		s.Add(c.Mul(c, c), d.Mul(d, d))
+		var re, im big.Rat
+		re.Add(&ac, &bd)
+		re.Quo(&re, &s)
+		im.Sub(&bc, &ad)
+		im.Quo(&im, &s)
+		return cmplx{&re, &im}
+	case token.EQL:
+		return a.Cmp(c) == 0 && b.Cmp(d) == 0
+	case token.NEQ:
+		return a.Cmp(c) != 0 || b.Cmp(d) != 0
+	}
+	panic("unreachable")
+}
+
+func binaryStringOp(x string, op token.Token, y string) interface{} {
+	switch op {
+	case token.ADD:
+		return x + y
+	case token.EQL:
+		return x == y
+	case token.NEQ:
+		return x != y
+	case token.LSS:
+		return x < y
+	case token.LEQ:
+		return x <= y
+	case token.GTR:
+		return x > y
+	case token.GEQ:
+		return x >= y
+	}
+	panic("unreachable")
+}
diff --git a/src/pkg/go/types/exportdata.go b/src/pkg/go/types/exportdata.go
new file mode 100644
index 000000000..383520320
--- /dev/null
+++ b/src/pkg/go/types/exportdata.go
@@ -0,0 +1,132 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements ExportData.
+
+package types
+
+import (
+	"bufio"
+	"fmt"
+	"io"
+	"os"
+	"strconv"
+	"strings"
+)
+
+func readGopackHeader(buf *bufio.Reader) (name string, size int, err os.Error) {
+	// See $GOROOT/include/ar.h.
+	hdr := make([]byte, 64+12+6+6+8+10+2)
+	_, err = io.ReadFull(buf, hdr)
+	if err != nil {
+		return
+	}
+	if trace {
+		fmt.Printf("header: %s", hdr)
+	}
+	s := strings.TrimSpace(string(hdr[64+12+6+6+8:][:10]))
+	size, err = strconv.Atoi(s)
+	if err != nil || hdr[len(hdr)-2] != '`' || hdr[len(hdr)-1] != '\n' {
+		err = os.NewError("invalid archive header")
+		return
+	}
+	name = strings.TrimSpace(string(hdr[:64]))
+	return
+}
+
+type dataReader struct {
+	*bufio.Reader
+	io.Closer
+}
+
+// ExportData returns a readCloser positioned at the beginning of the
+// export data section of the given object/archive file, or an error.
+// It is the caller's responsibility to close the readCloser.
+//
+func ExportData(filename string) (rc io.ReadCloser, err os.Error) {
+	file, err := os.Open(filename)
+	if err != nil {
+		return
+	}
+
+	defer func() {
+		if err != nil {
+			file.Close()
+			// Add file name to error.
+			err = fmt.Errorf("reading export data: %s: %v", filename, err)
+		}
+	}()
+
+	buf := bufio.NewReader(file)
+
+	// Read first line to make sure this is an object file.
+	line, err := buf.ReadSlice('\n')
+	if err != nil {
+		return
+	}
+	if string(line) == "!<arch>\n" {
+		// Archive file.  Scan to __.PKGDEF, which should
+		// be second archive entry.
+		var name string
+		var size int
+
+		// First entry should be __.SYMDEF.
+		// Read and discard.
+		if name, size, err = readGopackHeader(buf); err != nil {
+			return
+		}
+		if name != "__.SYMDEF" {
+			err = os.NewError("go archive does not begin with __.SYMDEF")
+			return
+		}
+		const block = 4096
+		tmp := make([]byte, block)
+		for size > 0 {
+			n := size
+			if n > block {
+				n = block
+			}
+			_, err = io.ReadFull(buf, tmp[:n])
+			if err != nil {
+				return
+			}
+			size -= n
+		}
+
+		// Second entry should be __.PKGDEF.
+		if name, size, err = readGopackHeader(buf); err != nil {
+			return
+		}
+		if name != "__.PKGDEF" {
+			err = os.NewError("go archive is missing __.PKGDEF")
+			return
+		}
+
+		// Read first line of __.PKGDEF data, so that line
+		// is once again the first line of the input.
+		line, err = buf.ReadSlice('\n')
+		if err != nil {
+			return
+		}
+	}
+
+	// Now at __.PKGDEF in archive or still at beginning of file.
+	// Either way, line should begin with "go object ".
+	if !strings.HasPrefix(string(line), "go object ") {
+		err = os.NewError("not a go object file")
+		return
+	}
+
+	// Skip over object header to export data.
+	// Begins after first line with $$.
+	for line[0] != '$' {
+		line, err = buf.ReadSlice('\n')
+		if err != nil {
+			return
+		}
+	}
+
+	rc = &dataReader{buf, file}
+	return
+}
diff --git a/src/pkg/go/types/gcimporter.go b/src/pkg/go/types/gcimporter.go
new file mode 100644
index 000000000..6ab1806b6
--- /dev/null
+++ b/src/pkg/go/types/gcimporter.go
@@ -0,0 +1,799 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file implements an ast.Importer for gc generated object files.
+// TODO(gri) Eventually move this into a separate package outside types.
+
+package types
+
+import (
+	"big"
+	"fmt"
+	"go/ast"
+	"go/token"
+	"io"
+	"os"
+	"path/filepath"
+	"runtime"
+	"scanner"
+	"strconv"
+)
+
+const trace = false // set to true for debugging
+
+var (
+	pkgRoot = filepath.Join(runtime.GOROOT(), "pkg", runtime.GOOS+"_"+runtime.GOARCH)
+	pkgExts = [...]string{".a", ".5", ".6", ".8"}
+)
+
+// findPkg returns the filename and package id for an import path.
+// If no file was found, an empty filename is returned.
+func findPkg(path string) (filename, id string) {
+	if len(path) == 0 {
+		return
+	}
+
+	id = path
+	var noext string
+	switch path[0] {
+	default:
+		// "x" -> "$GOROOT/pkg/$GOOS_$GOARCH/x.ext", "x"
+		noext = filepath.Join(pkgRoot, path)
+
+	case '.':
+		// "./x" -> "/this/directory/x.ext", "/this/directory/x"
+		cwd, err := os.Getwd()
+		if err != nil {
+			return
+		}
+		noext = filepath.Join(cwd, path)
+		id = noext
+
+	case '/':
+		// "/x" -> "/x.ext", "/x"
+		noext = path
+	}
+
+	// try extensions
+	for _, ext := range pkgExts {
+		filename = noext + ext
+		if f, err := os.Stat(filename); err == nil && f.IsRegular() {
+			return
+		}
+	}
+
+	filename = "" // not found
+	return
+}
+
+// gcParser parses the exports inside a gc compiler-produced
+// object/archive file and populates its scope with the results.
+type gcParser struct {
+	scanner scanner.Scanner
+	tok     int                    // current token
+	lit     string                 // literal string; only valid for Ident, Int, String tokens
+	id      string                 // package id of imported package
+	imports map[string]*ast.Object // package id -> package object
+}
+
+func (p *gcParser) init(filename, id string, src io.Reader, imports map[string]*ast.Object) {
+	p.scanner.Init(src)
+	p.scanner.Error = func(_ *scanner.Scanner, msg string) { p.error(msg) }
+	p.scanner.Mode = scanner.ScanIdents | scanner.ScanInts | scanner.ScanStrings | scanner.ScanComments | scanner.SkipComments
+	p.scanner.Whitespace = 1<<'\t' | 1<<' '
+	p.scanner.Filename = filename // for good error messages
+	p.next()
+	p.id = id
+	p.imports = imports
+}
+
+func (p *gcParser) next() {
+	p.tok = p.scanner.Scan()
+	switch p.tok {
+	case scanner.Ident, scanner.Int, scanner.String:
+		p.lit = p.scanner.TokenText()
+	default:
+		p.lit = ""
+	}
+	if trace {
+		fmt.Printf("%s: %q -> %q\n", scanner.TokenString(p.tok), p.scanner.TokenText(), p.lit)
+	}
+}
+
+// GcImporter implements the ast.Importer signature.
+func GcImporter(imports map[string]*ast.Object, path string) (pkg *ast.Object, err os.Error) {
+	if path == "unsafe" {
+		return Unsafe, nil
+	}
+
+	defer func() {
+		if r := recover(); r != nil {
+			err = r.(importError) // will re-panic if r is not an importError
+			if trace {
+				panic(err) // force a stack trace
+			}
+		}
+	}()
+
+	filename, id := findPkg(path)
+	if filename == "" {
+		err = os.NewError("can't find import: " + id)
+		return
+	}
+
+	if pkg = imports[id]; pkg != nil {
+		return // package was imported before
+	}
+
+	buf, err := ExportData(filename)
+	if err != nil {
+		return
+	}
+	defer buf.Close()
+
+	if trace {
+		fmt.Printf("importing %s (%s)\n", id, filename)
+	}
+
+	var p gcParser
+	p.init(filename, id, buf, imports)
+	pkg = p.parseExport()
+	return
+}
+
+// ----------------------------------------------------------------------------
+// Error handling
+
+// Internal errors are boxed as importErrors.
+type importError struct {
+	pos scanner.Position
+	err os.Error
+}
+
+func (e importError) String() string {
+	return fmt.Sprintf("import error %s (byte offset = %d): %s", e.pos, e.pos.Offset, e.err)
+}
+
+func (p *gcParser) error(err interface{}) {
+	if s, ok := err.(string); ok {
+		err = os.NewError(s)
+	}
+	// panic with a runtime.Error if err is not an os.Error
+	panic(importError{p.scanner.Pos(), err.(os.Error)})
+}
+
+func (p *gcParser) errorf(format string, args ...interface{}) {
+	p.error(fmt.Sprintf(format, args...))
+}
+
+func (p *gcParser) expect(tok int) string {
+	lit := p.lit
+	if p.tok != tok {
+		p.errorf("expected %q, got %q (%q)", scanner.TokenString(tok), scanner.TokenString(p.tok), lit)
+	}
+	p.next()
+	return lit
+}
+
+func (p *gcParser) expectSpecial(tok string) {
+	sep := 'x' // not white space
+	i := 0
+	for i < len(tok) && p.tok == int(tok[i]) && sep > ' ' {
+		sep = p.scanner.Peek() // if sep <= ' ', there is white space before the next token
+		p.next()
+		i++
+	}
+	if i < len(tok) {
+		p.errorf("expected %q, got %q", tok, tok[0:i])
+	}
+}
+
+func (p *gcParser) expectKeyword(keyword string) {
+	lit := p.expect(scanner.Ident)
+	if lit != keyword {
+		p.errorf("expected keyword %s, got %q", keyword, lit)
+	}
+}
+
+// ----------------------------------------------------------------------------
+// Import declarations
+
+// ImportPath = string_lit .
+//
+func (p *gcParser) parsePkgId() *ast.Object {
+	id, err := strconv.Unquote(p.expect(scanner.String))
+	if err != nil {
+		p.error(err)
+	}
+
+	switch id {
+	case "":
+		// id == "" stands for the imported package id
+		// (only known at time of package installation)
+		id = p.id
+	case "unsafe":
+		// package unsafe is not in the imports map - handle explicitly
+		return Unsafe
+	}
+
+	pkg := p.imports[id]
+	if pkg == nil {
+		scope = ast.NewScope(nil)
+		pkg = ast.NewObj(ast.Pkg, "")
+		pkg.Data = scope
+		p.imports[id] = pkg
+	}
+
+	return pkg
+}
+
+// dotIdentifier = ( ident | '·' ) { ident | int | '·' } .
+func (p *gcParser) parseDotIdent() string {
+	ident := ""
+	if p.tok != scanner.Int {
+		sep := 'x' // not white space
+		for (p.tok == scanner.Ident || p.tok == scanner.Int || p.tok == '·') && sep > ' ' {
+			ident += p.lit
+			sep = p.scanner.Peek() // if sep <= ' ', there is white space before the next token
+			p.next()
+		}
+	}
+	if ident == "" {
+		p.expect(scanner.Ident) // use expect() for error handling
+	}
+	return ident
+}
+
+// ExportedName = ImportPath "." dotIdentifier .
+//
+func (p *gcParser) parseExportedName(kind ast.ObjKind) *ast.Object {
+	pkg := p.parsePkgId()
+	p.expect('.')
+	name := p.parseDotIdent()
+
+	// a type may have been declared before - if it exists
+	// already in the respective package scope, return that
+	// type
+	scope := pkg.Data.(*ast.Scope)
+	if kind == ast.Typ {
+		if obj := scope.Lookup(name); obj != nil {
+			assert(obj.Kind == ast.Typ)
+			return obj
+		}
+	}
+
+	// any other object must be a newly declared object -
+	// create it and insert it into the package scope
+	obj := ast.NewObj(kind, name)
+	if scope.Insert(obj) != nil {
+		p.errorf("already declared: %s", obj.Name)
+	}
+
+	// a new type object is a named type and may be referred
+	// to before the underlying type is known - set it up
+	if kind == ast.Typ {
+		obj.Type = &Name{Obj: obj}
+	}
+
+	return obj
+}
+
+// ----------------------------------------------------------------------------
+// Types
+
+// BasicType = identifier .
+//
+func (p *gcParser) parseBasicType() Type {
+	obj := Universe.Lookup(p.expect(scanner.Ident))
+	if obj == nil || obj.Kind != ast.Typ {
+		p.errorf("not a basic type: %s", obj.Name)
+	}
+	return obj.Type.(Type)
+}
+
+// ArrayType = "[" int_lit "]" Type .
+//
+func (p *gcParser) parseArrayType() Type {
+	// "[" already consumed and lookahead known not to be "]"
+	lit := p.expect(scanner.Int)
+	p.expect(']')
+	elt := p.parseType()
+	n, err := strconv.Atoui64(lit)
+	if err != nil {
+		p.error(err)
+	}
+	return &Array{Len: n, Elt: elt}
+}
+
+// MapType = "map" "[" Type "]" Type .
+//
+func (p *gcParser) parseMapType() Type {
+	p.expectKeyword("map")
+	p.expect('[')
+	key := p.parseType()
+	p.expect(']')
+	elt := p.parseType()
+	return &Map{Key: key, Elt: elt}
+}
+
+// Name = identifier | "?" .
+//
+func (p *gcParser) parseName() (name string) {
+	switch p.tok {
+	case scanner.Ident:
+		name = p.lit
+		p.next()
+	case '?':
+		// anonymous
+		p.next()
+	default:
+		p.error("name expected")
+	}
+	return
+}
+
+// Field = Name Type [ ":" string_lit ] .
+//
+func (p *gcParser) parseField() (fld *ast.Object, tag string) {
+	name := p.parseName()
+	ftyp := p.parseType()
+	if name == "" {
+		// anonymous field - ftyp must be T or *T and T must be a type name
+		if _, ok := Deref(ftyp).(*Name); !ok {
+			p.errorf("anonymous field expected")
+		}
+	}
+	if p.tok == ':' {
+		p.next()
+		tag = p.expect(scanner.String)
+	}
+	fld = ast.NewObj(ast.Var, name)
+	fld.Type = ftyp
+	return
+}
+
+// StructType = "struct" "{" [ FieldList ] "}" .
+// FieldList  = Field { ";" Field } .
+//
+func (p *gcParser) parseStructType() Type {
+	var fields []*ast.Object
+	var tags []string
+
+	parseField := func() {
+		fld, tag := p.parseField()
+		fields = append(fields, fld)
+		tags = append(tags, tag)
+	}
+
+	p.expectKeyword("struct")
+	p.expect('{')
+	if p.tok != '}' {
+		parseField()
+		for p.tok == ';' {
+			p.next()
+			parseField()
+		}
+	}
+	p.expect('}')
+
+	return &Struct{Fields: fields, Tags: tags}
+}
+
+// Parameter = ( identifier | "?" ) [ "..." ] Type [ ":" string_lit ] .
+//
+func (p *gcParser) parseParameter() (par *ast.Object, isVariadic bool) {
+	name := p.parseName()
+	if name == "" {
+		name = "_" // cannot access unnamed identifiers
+	}
+	if p.tok == '.' {
+		p.expectSpecial("...")
+		isVariadic = true
+	}
+	ptyp := p.parseType()
+	// ignore argument tag
+	if p.tok == ':' {
+		p.next()
+		p.expect(scanner.String)
+	}
+	par = ast.NewObj(ast.Var, name)
+	par.Type = ptyp
+	return
+}
+
+// Parameters    = "(" [ ParameterList ] ")" .
+// ParameterList = { Parameter "," } Parameter .
+//
+func (p *gcParser) parseParameters() (list []*ast.Object, isVariadic bool) {
+	parseParameter := func() {
+		par, variadic := p.parseParameter()
+		list = append(list, par)
+		if variadic {
+			if isVariadic {
+				p.error("... not on final argument")
+			}
+			isVariadic = true
+		}
+	}
+
+	p.expect('(')
+	if p.tok != ')' {
+		parseParameter()
+		for p.tok == ',' {
+			p.next()
+			parseParameter()
+		}
+	}
+	p.expect(')')
+
+	return
+}
+
+// Signature = Parameters [ Result ] .
+// Result    = Type | Parameters .
+//
+func (p *gcParser) parseSignature() *Func {
+	params, isVariadic := p.parseParameters()
+
+	// optional result type
+	var results []*ast.Object
+	switch p.tok {
+	case scanner.Ident, scanner.String, '[', '*', '<':
+		// single, unnamed result
+		result := ast.NewObj(ast.Var, "_")
+		result.Type = p.parseType()
+		results = []*ast.Object{result}
+	case '(':
+		// named or multiple result(s)
+		var variadic bool
+		results, variadic = p.parseParameters()
+		if variadic {
+			p.error("... not permitted on result type")
+		}
+	}
+
+	return &Func{Params: params, Results: results, IsVariadic: isVariadic}
+}
+
+// MethodSpec = identifier Signature .
+//
+func (p *gcParser) parseMethodSpec() *ast.Object {
+	if p.tok == scanner.Ident {
+		p.expect(scanner.Ident)
+	} else {
+		// TODO(gri) should this be parseExportedName here?
+		p.parsePkgId()
+		p.expect('.')
+		p.parseDotIdent()
+	}
+	p.parseSignature()
+
+	// TODO(gri) compute method object
+	return ast.NewObj(ast.Fun, "_")
+}
+
+// InterfaceType = "interface" "{" [ MethodList ] "}" .
+// MethodList    = MethodSpec { ";" MethodSpec } .
+//
+func (p *gcParser) parseInterfaceType() Type {
+	var methods ObjList
+
+	parseMethod := func() {
+		meth := p.parseMethodSpec()
+		methods = append(methods, meth)
+	}
+
+	p.expectKeyword("interface")
+	p.expect('{')
+	if p.tok != '}' {
+		parseMethod()
+		for p.tok == ';' {
+			p.next()
+			parseMethod()
+		}
+	}
+	p.expect('}')
+
+	methods.Sort()
+	return &Interface{Methods: methods}
+}
+
+// ChanType = ( "chan" [ "<-" ] | "<-" "chan" ) Type .
+//
+func (p *gcParser) parseChanType() Type {
+	dir := ast.SEND | ast.RECV
+	if p.tok == scanner.Ident {
+		p.expectKeyword("chan")
+		if p.tok == '<' {
+			p.expectSpecial("<-")
+			dir = ast.SEND
+		}
+	} else {
+		p.expectSpecial("<-")
+		p.expectKeyword("chan")
+		dir = ast.RECV
+	}
+	elt := p.parseType()
+	return &Chan{Dir: dir, Elt: elt}
+}
+
+// Type =
+//	BasicType | TypeName | ArrayType | SliceType | StructType |
+//      PointerType | FuncType | InterfaceType | MapType | ChanType |
+//      "(" Type ")" .
+// BasicType = ident .
+// TypeName = ExportedName .
+// SliceType = "[" "]" Type .
+// PointerType = "*" Type .
+// FuncType = "func" Signature .
+//
+func (p *gcParser) parseType() Type {
+	switch p.tok {
+	case scanner.Ident:
+		switch p.lit {
+		default:
+			return p.parseBasicType()
+		case "struct":
+			return p.parseStructType()
+		case "func":
+			// FuncType
+			p.next()
+			return p.parseSignature()
+		case "interface":
+			return p.parseInterfaceType()
+		case "map":
+			return p.parseMapType()
+		case "chan":
+			return p.parseChanType()
+		}
+	case scanner.String:
+		// TypeName
+		return p.parseExportedName(ast.Typ).Type.(Type)
+	case '[':
+		p.next() // look ahead
+		if p.tok == ']' {
+			// SliceType
+			p.next()
+			return &Slice{Elt: p.parseType()}
+		}
+		return p.parseArrayType()
+	case '*':
+		// PointerType
+		p.next()
+		return &Pointer{Base: p.parseType()}
+	case '<':
+		return p.parseChanType()
+	case '(':
+		// "(" Type ")"
+		p.next()
+		typ := p.parseType()
+		p.expect(')')
+		return typ
+	}
+	p.errorf("expected type, got %s (%q)", scanner.TokenString(p.tok), p.lit)
+	return nil
+}
+
+// ----------------------------------------------------------------------------
+// Declarations
+
+// ImportDecl = "import" identifier string_lit .
+//
+func (p *gcParser) parseImportDecl() {
+	p.expectKeyword("import")
+	// The identifier has no semantic meaning in the import data.
+	// It exists so that error messages can print the real package
+	// name: binary.ByteOrder instead of "encoding/binary".ByteOrder.
+	name := p.expect(scanner.Ident)
+	pkg := p.parsePkgId()
+	assert(pkg.Name == "" || pkg.Name == name)
+	pkg.Name = name
+}
+
+// int_lit = [ "+" | "-" ] { "0" ... "9" } .
+//
+func (p *gcParser) parseInt() (sign, val string) {
+	switch p.tok {
+	case '-':
+		p.next()
+		sign = "-"
+	case '+':
+		p.next()
+	}
+	val = p.expect(scanner.Int)
+	return
+}
+
+// number = int_lit [ "p" int_lit ] .
+//
+func (p *gcParser) parseNumber() Const {
+	// mantissa
+	sign, val := p.parseInt()
+	mant, ok := new(big.Int).SetString(sign+val, 10)
+	assert(ok)
+
+	if p.lit == "p" {
+		// exponent (base 2)
+		p.next()
+		sign, val = p.parseInt()
+		exp, err := strconv.Atoui(val)
+		if err != nil {
+			p.error(err)
+		}
+		if sign == "-" {
+			denom := big.NewInt(1)
+			denom.Lsh(denom, exp)
+			return Const{new(big.Rat).SetFrac(mant, denom)}
+		}
+		if exp > 0 {
+			mant.Lsh(mant, exp)
+		}
+		return Const{new(big.Rat).SetInt(mant)}
+	}
+
+	return Const{mant}
+}
+
+// ConstDecl   = "const" ExportedName [ Type ] "=" Literal .
+// Literal     = bool_lit | int_lit | float_lit | complex_lit | string_lit .
+// bool_lit    = "true" | "false" .
+// complex_lit = "(" float_lit "+" float_lit ")" .
+// string_lit  = `"` { unicode_char } `"` .
+//
+func (p *gcParser) parseConstDecl() {
+	p.expectKeyword("const")
+	obj := p.parseExportedName(ast.Con)
+	var x Const
+	var typ Type
+	if p.tok != '=' {
+		obj.Type = p.parseType()
+	}
+	p.expect('=')
+	switch p.tok {
+	case scanner.Ident:
+		// bool_lit
+		if p.lit != "true" && p.lit != "false" {
+			p.error("expected true or false")
+		}
+		x = Const{p.lit == "true"}
+		typ = Bool.Underlying
+		p.next()
+	case '-', scanner.Int:
+		// int_lit
+		x = p.parseNumber()
+		typ = Int.Underlying
+		if _, ok := x.val.(*big.Rat); ok {
+			typ = Float64.Underlying
+		}
+	case '(':
+		// complex_lit
+		p.next()
+		re := p.parseNumber()
+		p.expect('+')
+		im := p.parseNumber()
+		p.expect(')')
+		x = Const{cmplx{re.val.(*big.Rat), im.val.(*big.Rat)}}
+		typ = Complex128.Underlying
+	case scanner.String:
+		// string_lit
+		x = MakeConst(token.STRING, p.lit)
+		p.next()
+		typ = String.Underlying
+	default:
+		p.error("expected literal")
+	}
+	if obj.Type == nil {
+		obj.Type = typ
+	}
+	obj.Data = x
+}
+
+// TypeDecl = "type" ExportedName Type .
+//
+func (p *gcParser) parseTypeDecl() {
+	p.expectKeyword("type")
+	obj := p.parseExportedName(ast.Typ)
+
+	// The type object may have been imported before and thus already
+	// have a type associated with it. We still need to parse the type
+	// structure, but throw it away if the object already has a type.
+	// This ensures that all imports refer to the same type object for
+	// a given type declaration.
+	typ := p.parseType()
+
+	if name := obj.Type.(*Name); name.Underlying == nil {
+		assert(Underlying(typ) == typ)
+		name.Underlying = typ
+	}
+}
+
+// VarDecl = "var" ExportedName Type .
+//
+func (p *gcParser) parseVarDecl() {
+	p.expectKeyword("var")
+	obj := p.parseExportedName(ast.Var)
+	obj.Type = p.parseType()
+}
+
+// FuncDecl = "func" ExportedName Signature .
+//
+func (p *gcParser) parseFuncDecl() {
+	// "func" already consumed
+	obj := p.parseExportedName(ast.Fun)
+	obj.Type = p.parseSignature()
+}
+
+// MethodDecl = "func" Receiver identifier Signature .
+// Receiver   = "(" ( identifier | "?" ) [ "*" ] ExportedName ")" .
+//
+func (p *gcParser) parseMethodDecl() {
+	// "func" already consumed
+	p.expect('(')
+	p.parseParameter() // receiver
+	p.expect(')')
+	p.expect(scanner.Ident)
+	p.parseSignature()
+}
+
+// Decl = [ ImportDecl | ConstDecl | TypeDecl | VarDecl | FuncDecl | MethodDecl ] "\n" .
+//
+func (p *gcParser) parseDecl() {
+	switch p.lit {
+	case "import":
+		p.parseImportDecl()
+	case "const":
+		p.parseConstDecl()
+	case "type":
+		p.parseTypeDecl()
+	case "var":
+		p.parseVarDecl()
+	case "func":
+		p.next() // look ahead
+		if p.tok == '(' {
+			p.parseMethodDecl()
+		} else {
+			p.parseFuncDecl()
+		}
+	}
+	p.expect('\n')
+}
+
+// ----------------------------------------------------------------------------
+// Export
+
+// Export        = "PackageClause { Decl } "$$" .
+// PackageClause = "package" identifier [ "safe" ] "\n" .
+//
+func (p *gcParser) parseExport() *ast.Object {
+	p.expectKeyword("package")
+	name := p.expect(scanner.Ident)
+	if p.tok != '\n' {
+		// A package is safe if it was compiled with the -u flag,
+		// which disables the unsafe package.
+		// TODO(gri) remember "safe" package
+		p.expectKeyword("safe")
+	}
+	p.expect('\n')
+
+	assert(p.imports[p.id] == nil)
+	pkg := ast.NewObj(ast.Pkg, name)
+	pkg.Data = ast.NewScope(nil)
+	p.imports[p.id] = pkg
+
+	for p.tok != '$' && p.tok != scanner.EOF {
+		p.parseDecl()
+	}
+
+	if ch := p.scanner.Peek(); p.tok != '$' || ch != '$' {
+		// don't call next()/expect() since reading past the
+		// export data may cause scanner errors (e.g. NUL chars)
+		p.errorf("expected '$$', got %s %c", scanner.TokenString(p.tok), ch)
+	}
+
+	if n := p.scanner.ErrorCount; n != 0 {
+		p.errorf("expected no scanner errors, got %d", n)
+	}
+
+	return pkg
+}
diff --git a/src/pkg/go/types/gcimporter_test.go b/src/pkg/go/types/gcimporter_test.go
new file mode 100644
index 000000000..ec87f5d51
--- /dev/null
+++ b/src/pkg/go/types/gcimporter_test.go
@@ -0,0 +1,101 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package types
+
+import (
+	"exec"
+	"go/ast"
+	"io/ioutil"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"testing"
+	"time"
+)
+
+var gcName, gcPath string // compiler name and path
+
+func init() {
+	// determine compiler
+	switch runtime.GOARCH {
+	case "386":
+		gcName = "8g"
+	case "amd64":
+		gcName = "6g"
+	case "arm":
+		gcName = "5g"
+	default:
+		gcName = "unknown-GOARCH-compiler"
+		gcPath = gcName
+		return
+	}
+	gcPath, _ = exec.LookPath(gcName)
+}
+
+func compile(t *testing.T, dirname, filename string) {
+	cmd := exec.Command(gcPath, filename)
+	cmd.Dir = dirname
+	out, err := cmd.CombinedOutput()
+	if err != nil {
+		t.Errorf("%s %s failed: %s", gcName, filename, err)
+		return
+	}
+	t.Logf("%s", string(out))
+}
+
+// Use the same global imports map for all tests. The effect is
+// as if all tested packages were imported into a single package.
+var imports = make(map[string]*ast.Object)
+
+func testPath(t *testing.T, path string) bool {
+	_, err := GcImporter(imports, path)
+	if err != nil {
+		t.Errorf("testPath(%s): %s", path, err)
+		return false
+	}
+	return true
+}
+
+const maxTime = 3e9 // maximum allotted testing time in ns
+
+func testDir(t *testing.T, dir string, endTime int64) (nimports int) {
+	dirname := filepath.Join(pkgRoot, dir)
+	list, err := ioutil.ReadDir(dirname)
+	if err != nil {
+		t.Errorf("testDir(%s): %s", dirname, err)
+	}
+	for _, f := range list {
+		if time.Nanoseconds() >= endTime {
+			t.Log("testing time used up")
+			return
+		}
+		switch {
+		case f.IsRegular():
+			// try extensions
+			for _, ext := range pkgExts {
+				if strings.HasSuffix(f.Name, ext) {
+					name := f.Name[0 : len(f.Name)-len(ext)] // remove extension
+					if testPath(t, filepath.Join(dir, name)) {
+						nimports++
+					}
+				}
+			}
+		case f.IsDirectory():
+			nimports += testDir(t, filepath.Join(dir, f.Name), endTime)
+		}
+	}
+	return
+}
+
+func TestGcImport(t *testing.T) {
+	compile(t, "testdata", "exports.go")
+
+	nimports := 0
+	if testPath(t, "./testdata/exports") {
+		nimports++
+	}
+	nimports += testDir(t, "", time.Nanoseconds()+maxTime) // installed packages
+	t.Logf("tested %d imports", nimports)
+}
diff --git a/src/pkg/go/types/testdata/exports.go b/src/pkg/go/types/testdata/exports.go
new file mode 100644
index 000000000..ed63bf9ad
--- /dev/null
+++ b/src/pkg/go/types/testdata/exports.go
@@ -0,0 +1,84 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This file is used to generate an object file which
+// serves as test file for gcimporter_test.go.
+
+package exports
+
+import (
+	"go/ast"
+)
+
+const (
+	C0 int = 0
+	C1     = 3.14159265
+	C2     = 2.718281828i
+	C3     = -123.456e-789
+	C4     = +123.456E+789
+	C5     = 1234i
+	C6     = "foo\n"
+	C7     = `bar\n`
+)
+
+type (
+	T1  int
+	T2  [10]int
+	T3  []int
+	T4  *int
+	T5  chan int
+	T6a chan<- int
+	T6b chan (<-chan int)
+	T6c chan<- (chan int)
+	T7  <-chan *ast.File
+	T8  struct{}
+	T9  struct {
+		a    int
+		b, c float32
+		d    []string `go:"tag"`
+	}
+	T10 struct {
+		T8
+		T9
+		_ *T10
+	}
+	T11 map[int]string
+	T12 interface{}
+	T13 interface {
+		m1()
+		m2(int) float32
+	}
+	T14 interface {
+		T12
+		T13
+		m3(x ...struct{}) []T9
+	}
+	T15 func()
+	T16 func(int)
+	T17 func(x int)
+	T18 func() float32
+	T19 func() (x float32)
+	T20 func(...interface{})
+	T21 struct{ next *T21 }
+	T22 struct{ link *T23 }
+	T23 struct{ link *T22 }
+	T24 *T24
+	T25 *T26
+	T26 *T27
+	T27 *T25
+	T28 func(T28) T28
+)
+
+var (
+	V0 int
+	V1 = -991.0
+)
+
+func F1()         {}
+func F2(x int)    {}
+func F3() int     { return 0 }
+func F4() float32 { return 0 }
+func F5(a, b, c int, u, v, w struct{ x, y T1 }, more ...interface{}) (p, q, r chan<- T10)
+
+func (p *T1) M1()
diff --git a/src/pkg/go/types/testdata/test0.src b/src/pkg/go/types/testdata/test0.src
new file mode 100644
index 000000000..84a1abe27
--- /dev/null
+++ b/src/pkg/go/types/testdata/test0.src
@@ -0,0 +1,154 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// type declarations
+
+package test0
+
+import "unsafe"
+
+const pi = 3.1415
+
+type (
+	N undeclared /* ERROR "undeclared" */
+	B bool
+	I int32
+	A [10]P
+	T struct {
+		x, y P
+	}
+	P *T
+	R (*R)
+	F func(A) I
+	Y interface {
+		f(A) I
+	}
+	S [](((P)))
+	M map[I]F
+	C chan<- I
+)
+
+
+type (
+	p1 pi /* ERROR "not a package" */ .foo
+	p2 unsafe.Pointer
+)
+
+
+type (
+	Pi pi /* ERROR "not a type" */
+
+	a /* DISABLED "illegal cycle" */ a
+	a /* ERROR "redeclared" */ int
+
+	// where the cycle error appears depends on the
+	// order in which declarations are processed
+	// (which depends on the order in which a map
+	// is iterated through)
+	b c
+	c /* DISABLED "illegal cycle" */ d
+	d e
+	e b
+
+	t *t
+
+	U V
+	V *W
+	W U
+
+	P1 *S2
+	P2 P1
+
+	S0 struct {
+	}
+	S1 struct {
+		a, b, c int
+		u, v, a /* ERROR "redeclared" */ float32
+	}
+	S2 struct {
+		U // anonymous field
+		// TODO(gri) recognize double-declaration below
+		// U /* ERROR "redeclared" */ int
+	}
+	S3 struct {
+		x S2
+	}
+	S4/* DISABLED "illegal cycle" */ struct {
+		S4
+	}
+	S5 struct {
+		S6
+	}
+	S6 /* DISABLED "illegal cycle" */ struct {
+		field S7
+	}
+	S7 struct {
+		S5
+	}
+
+	L1 []L1
+	L2 []int
+
+	A1 [10]int
+	A2 /* DISABLED "illegal cycle" */ [10]A2
+	A3 /* DISABLED "illegal cycle" */ [10]struct {
+		x A4
+	}
+	A4 [10]A3
+
+	F1 func()
+	F2 func(x, y, z float32)
+	F3 func(x, y, x /* ERROR "redeclared" */ float32)
+	F4 func() (x, y, x /* ERROR "redeclared" */ float32)
+	F5 func(x int) (x /* ERROR "redeclared" */ float32)
+	F6 func(x ...int)
+
+	I1 interface{}
+	I2 interface {
+		m1()
+	}
+	I3 interface {
+		m1()
+		m1 /* ERROR "redeclared" */ ()
+	}
+	I4 interface {
+		m1(x, y, x /* ERROR "redeclared" */ float32)
+		m2() (x, y, x /* ERROR "redeclared" */ float32)
+		m3(x int) (x /* ERROR "redeclared" */ float32)
+	}
+	I5 interface {
+		m1(I5)
+	}
+	I6 interface {
+		S0 /* ERROR "non-interface" */
+	}
+	I7 interface {
+		I1
+		I1
+	}
+	I8 /* DISABLED "illegal cycle" */ interface {
+		I8
+	}
+	I9 /* DISABLED "illegal cycle" */ interface {
+		I10
+	}
+	I10 interface {
+		I11
+	}
+	I11 interface {
+		I9
+	}
+
+	C1 chan int
+	C2 <-chan int
+	C3 chan<- C3
+	C4 chan C5
+	C5 chan C6
+	C6 chan C4
+
+	M1 map[Last]string
+	M2 map[string]M2
+
+	Last int
+)
diff --git a/src/pkg/go/types/types.go b/src/pkg/go/types/types.go
new file mode 100644
index 000000000..3aa896892
--- /dev/null
+++ b/src/pkg/go/types/types.go
@@ -0,0 +1,255 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// PACKAGE UNDER CONSTRUCTION. ANY AND ALL PARTS MAY CHANGE.
+// Package types declares the types used to represent Go types.
+//
+package types
+
+import (
+	"go/ast"
+	"sort"
+)
+
+// All types implement the Type interface.
+type Type interface {
+	isType()
+}
+
+// All concrete types embed ImplementsType which
+// ensures that all types implement the Type interface.
+type ImplementsType struct{}
+
+func (t *ImplementsType) isType() {}
+
+// A Bad type is a non-nil placeholder type when we don't know a type.
+type Bad struct {
+	ImplementsType
+	Msg string // for better error reporting/debugging
+}
+
+// A Basic represents a (unnamed) basic type.
+type Basic struct {
+	ImplementsType
+	// TODO(gri) need a field specifying the exact basic type
+}
+
+// An Array represents an array type [Len]Elt.
+type Array struct {
+	ImplementsType
+	Len uint64
+	Elt Type
+}
+
+// A Slice represents a slice type []Elt.
+type Slice struct {
+	ImplementsType
+	Elt Type
+}
+
+// A Struct represents a struct type struct{...}.
+// Anonymous fields are represented by objects with empty names.
+type Struct struct {
+	ImplementsType
+	Fields ObjList  // struct fields; or nil
+	Tags   []string // corresponding tags; or nil
+	// TODO(gri) This type needs some rethinking:
+	// - at the moment anonymous fields are marked with "" object names,
+	//   and their names have to be reconstructed
+	// - there is no scope for fast lookup (but the parser creates one)
+}
+
+// A Pointer represents a pointer type *Base.
+type Pointer struct {
+	ImplementsType
+	Base Type
+}
+
+// A Func represents a function type func(...) (...).
+// Unnamed parameters are represented by objects with empty names.
+type Func struct {
+	ImplementsType
+	Recv       *ast.Object // nil if not a method
+	Params     ObjList     // (incoming) parameters from left to right; or nil
+	Results    ObjList     // (outgoing) results from left to right; or nil
+	IsVariadic bool        // true if the last parameter's type is of the form ...T
+}
+
+// An Interface represents an interface type interface{...}.
+type Interface struct {
+	ImplementsType
+	Methods ObjList // interface methods sorted by name; or nil
+}
+
+// A Map represents a map type map[Key]Elt.
+type Map struct {
+	ImplementsType
+	Key, Elt Type
+}
+
+// A Chan represents a channel type chan Elt, <-chan Elt, or chan<-Elt.
+type Chan struct {
+	ImplementsType
+	Dir ast.ChanDir
+	Elt Type
+}
+
+// A Name represents a named type as declared in a type declaration.
+type Name struct {
+	ImplementsType
+	Underlying Type        // nil if not fully declared
+	Obj        *ast.Object // corresponding declared object
+	// TODO(gri) need to remember fields and methods.
+}
+
+// If typ is a pointer type, Deref returns the pointer's base type;
+// otherwise it returns typ.
+func Deref(typ Type) Type {
+	if typ, ok := typ.(*Pointer); ok {
+		return typ.Base
+	}
+	return typ
+}
+
+// Underlying returns the underlying type of a type.
+func Underlying(typ Type) Type {
+	if typ, ok := typ.(*Name); ok {
+		utyp := typ.Underlying
+		if _, ok := utyp.(*Basic); !ok {
+			return utyp
+		}
+		// the underlying type of a type name referring
+		// to an (untyped) basic type is the basic type
+		// name
+	}
+	return typ
+}
+
+// An ObjList represents an ordered (in some fashion) list of objects.
+type ObjList []*ast.Object
+
+// ObjList implements sort.Interface.
+func (list ObjList) Len() int           { return len(list) }
+func (list ObjList) Less(i, j int) bool { return list[i].Name < list[j].Name }
+func (list ObjList) Swap(i, j int)      { list[i], list[j] = list[j], list[i] }
+
+// Sort sorts an object list by object name.
+func (list ObjList) Sort() { sort.Sort(list) }
+
+// identicalTypes returns true if both lists a and b have the
+// same length and corresponding objects have identical types.
+func identicalTypes(a, b ObjList) bool {
+	if len(a) == len(b) {
+		for i, x := range a {
+			y := b[i]
+			if !Identical(x.Type.(Type), y.Type.(Type)) {
+				return false
+			}
+		}
+		return true
+	}
+	return false
+}
+
+// Identical returns true if two types are identical.
+func Identical(x, y Type) bool {
+	if x == y {
+		return true
+	}
+
+	switch x := x.(type) {
+	case *Bad:
+		// A Bad type is always identical to any other type
+		// (to avoid spurious follow-up errors).
+		return true
+
+	case *Basic:
+		if y, ok := y.(*Basic); ok {
+			panic("unimplemented")
+			_ = y
+		}
+
+	case *Array:
+		// Two array types are identical if they have identical element types
+		// and the same array length.
+		if y, ok := y.(*Array); ok {
+			return x.Len == y.Len && Identical(x.Elt, y.Elt)
+		}
+
+	case *Slice:
+		// Two slice types are identical if they have identical element types.
+		if y, ok := y.(*Slice); ok {
+			return Identical(x.Elt, y.Elt)
+		}
+
+	case *Struct:
+		// Two struct types are identical if they have the same sequence of fields,
+		// and if corresponding fields have the same names, and identical types,
+		// and identical tags. Two anonymous fields are considered to have the same
+		// name. Lower-case field names from different packages are always different.
+		if y, ok := y.(*Struct); ok {
+			// TODO(gri) handle structs from different packages
+			if identicalTypes(x.Fields, y.Fields) {
+				for i, f := range x.Fields {
+					g := y.Fields[i]
+					if f.Name != g.Name || x.Tags[i] != y.Tags[i] {
+						return false
+					}
+				}
+				return true
+			}
+		}
+
+	case *Pointer:
+		// Two pointer types are identical if they have identical base types.
+		if y, ok := y.(*Pointer); ok {
+			return Identical(x.Base, y.Base)
+		}
+
+	case *Func:
+		// Two function types are identical if they have the same number of parameters
+		// and result values, corresponding parameter and result types are identical,
+		// and either both functions are variadic or neither is. Parameter and result
+		// names are not required to match.
+		if y, ok := y.(*Func); ok {
+			return identicalTypes(x.Params, y.Params) &&
+				identicalTypes(x.Results, y.Results) &&
+				x.IsVariadic == y.IsVariadic
+		}
+
+	case *Interface:
+		// Two interface types are identical if they have the same set of methods with
+		// the same names and identical function types. Lower-case method names from
+		// different packages are always different. The order of the methods is irrelevant.
+		if y, ok := y.(*Interface); ok {
+			return identicalTypes(x.Methods, y.Methods) // methods are sorted
+		}
+
+	case *Map:
+		// Two map types are identical if they have identical key and value types.
+		if y, ok := y.(*Map); ok {
+			return Identical(x.Key, y.Key) && Identical(x.Elt, y.Elt)
+		}
+
+	case *Chan:
+		// Two channel types are identical if they have identical value types
+		// and the same direction.
+		if y, ok := y.(*Chan); ok {
+			return x.Dir == y.Dir && Identical(x.Elt, y.Elt)
+		}
+
+	case *Name:
+		// Two named types are identical if their type names originate
+		// in the same type declaration.
+		if y, ok := y.(*Name); ok {
+			return x.Obj == y.Obj ||
+				// permit bad objects to be equal to avoid
+				// follow up errors
+				x.Obj != nil && x.Obj.Kind == ast.Bad ||
+				y.Obj != nil && y.Obj.Kind == ast.Bad
+		}
+	}
+
+	return false
+}
diff --git a/src/pkg/go/types/universe.go b/src/pkg/go/types/universe.go
new file mode 100644
index 000000000..6ae88e5f9
--- /dev/null
+++ b/src/pkg/go/types/universe.go
@@ -0,0 +1,108 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// FILE UNDER CONSTRUCTION. ANY AND ALL PARTS MAY CHANGE.
+// This file implements the universe and unsafe package scopes.
+
+package types
+
+import "go/ast"
+
+var (
+	scope    *ast.Scope // current scope to use for initialization
+	Universe *ast.Scope
+	Unsafe   *ast.Object // package unsafe
+)
+
+func define(kind ast.ObjKind, name string) *ast.Object {
+	obj := ast.NewObj(kind, name)
+	if scope.Insert(obj) != nil {
+		panic("types internal error: double declaration")
+	}
+	return obj
+}
+
+func defType(name string) *Name {
+	obj := define(ast.Typ, name)
+	typ := &Name{Underlying: &Basic{}, Obj: obj}
+	obj.Type = typ
+	return typ
+}
+
+func defConst(name string) {
+	obj := define(ast.Con, name)
+	_ = obj // TODO(gri) fill in other properties
+}
+
+func defFun(name string) {
+	obj := define(ast.Fun, name)
+	_ = obj // TODO(gri) fill in other properties
+}
+
+var (
+	Bool,
+	Int,
+	Float64,
+	Complex128,
+	String *Name
+)
+
+func init() {
+	scope = ast.NewScope(nil)
+	Universe = scope
+
+	Bool = defType("bool")
+	defType("byte") // TODO(gri) should be an alias for uint8
+	defType("complex64")
+	Complex128 = defType("complex128")
+	defType("float32")
+	Float64 = defType("float64")
+	defType("int8")
+	defType("int16")
+	defType("int32")
+	defType("int64")
+	String = defType("string")
+	defType("uint8")
+	defType("uint16")
+	defType("uint32")
+	defType("uint64")
+	Int = defType("int")
+	defType("uint")
+	defType("uintptr")
+
+	defConst("true")
+	defConst("false")
+	defConst("iota")
+	defConst("nil")
+
+	defFun("append")
+	defFun("cap")
+	defFun("close")
+	defFun("complex")
+	defFun("copy")
+	defFun("imag")
+	defFun("len")
+	defFun("make")
+	defFun("new")
+	defFun("panic")
+	defFun("print")
+	defFun("println")
+	defFun("real")
+	defFun("recover")
+
+	scope = ast.NewScope(nil)
+	Unsafe = ast.NewObj(ast.Pkg, "unsafe")
+	Unsafe.Data = scope
+
+	defType("Pointer")
+
+	defFun("Alignof")
+	defFun("New")
+	defFun("NewArray")
+	defFun("Offsetof")
+	defFun("Reflect")
+	defFun("Sizeof")
+	defFun("Typeof")
+	defFun("Unreflect")
+}