1 files changed, 266 insertions, 0 deletions
diff --git a/src/go/format/format.go b/src/go/format/format.go
new file mode 100644
index 000000000..668a42df2
--- /dev/null
+++ b/src/go/format/format.go
@@ -0,0 +1,266 @@
+// Copyright 2012 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 format implements standard formatting of Go source.
+package format
+
+import (
+	"bytes"
+	"fmt"
+	"go/ast"
+	"go/parser"
+	"go/printer"
+	"go/token"
+	"io"
+	"strings"
+)
+
+var config = printer.Config{Mode: printer.UseSpaces | printer.TabIndent, Tabwidth: 8}
+
+const parserMode = parser.ParseComments
+
+// Node formats node in canonical gofmt style and writes the result to dst.
+//
+// The node type must be *ast.File, *printer.CommentedNode, []ast.Decl,
+// []ast.Stmt, or assignment-compatible to ast.Expr, ast.Decl, ast.Spec,
+// or ast.Stmt. Node does not modify node. Imports are not sorted for
+// nodes representing partial source files (i.e., if the node is not an
+// *ast.File or a *printer.CommentedNode not wrapping an *ast.File).
+//
+// The function may return early (before the entire result is written)
+// and return a formatting error, for instance due to an incorrect AST.
+//
+func Node(dst io.Writer, fset *token.FileSet, node interface{}) error {
+	// Determine if we have a complete source file (file != nil).
+	var file *ast.File
+	var cnode *printer.CommentedNode
+	switch n := node.(type) {
+	case *ast.File:
+		file = n
+	case *printer.CommentedNode:
+		if f, ok := n.Node.(*ast.File); ok {
+			file = f
+			cnode = n
+		}
+	}
+
+	// Sort imports if necessary.
+	if file != nil && hasUnsortedImports(file) {
+		// Make a copy of the AST because ast.SortImports is destructive.
+		// TODO(gri) Do this more efficiently.
+		var buf bytes.Buffer
+		err := config.Fprint(&buf, fset, file)
+		if err != nil {
+			return err
+		}
+		file, err = parser.ParseFile(fset, "", buf.Bytes(), parserMode)
+		if err != nil {
+			// We should never get here. If we do, provide good diagnostic.
+			return fmt.Errorf("format.Node internal error (%s)", err)
+		}
+		ast.SortImports(fset, file)
+
+		// Use new file with sorted imports.
+		node = file
+		if cnode != nil {
+			node = &printer.CommentedNode{Node: file, Comments: cnode.Comments}
+		}
+	}
+
+	return config.Fprint(dst, fset, node)
+}
+
+// Source formats src in canonical gofmt style and returns the result
+// or an (I/O or syntax) error. src is expected to be a syntactically
+// correct Go source file, or a list of Go declarations or statements.
+//
+// If src is a partial source file, the leading and trailing space of src
+// is applied to the result (such that it has the same leading and trailing
+// space as src), and the result is indented by the same amount as the first
+// line of src containing code. Imports are not sorted for partial source files.
+//
+func Source(src []byte) ([]byte, error) {
+	fset := token.NewFileSet()
+	file, sourceAdj, indentAdj, err := parse(fset, "", src, true)
+	if err != nil {
+		return nil, err
+	}
+
+	if sourceAdj == nil {
+		// Complete source file.
+		// TODO(gri) consider doing this always.
+		ast.SortImports(fset, file)
+	}
+
+	return format(fset, file, sourceAdj, indentAdj, src, config)
+}
+
+func hasUnsortedImports(file *ast.File) bool {
+	for _, d := range file.Decls {
+		d, ok := d.(*ast.GenDecl)
+		if !ok || d.Tok != token.IMPORT {
+			// Not an import declaration, so we're done.
+			// Imports are always first.
+			return false
+		}
+		if d.Lparen.IsValid() {
+			// For now assume all grouped imports are unsorted.
+			// TODO(gri) Should check if they are sorted already.
+			return true
+		}
+		// Ungrouped imports are sorted by default.
+	}
+	return false
+}
+
+// ----------------------------------------------------------------------------
+// Support functions
+//
+// The functions parse, format, and isSpace below are identical to the
+// respective functions in cmd/gofmt/gofmt.go - keep them in sync!
+//
+// TODO(gri) Factor out this functionality, eventually.
+
+// parse parses src, which was read from the named file,
+// as a Go source file, declaration, or statement list.
+func parse(fset *token.FileSet, filename string, src []byte, fragmentOk bool) (
+	file *ast.File,
+	sourceAdj func(src []byte, indent int) []byte,
+	indentAdj int,
+	err error,
+) {
+	// Try as whole source file.
+	file, err = parser.ParseFile(fset, filename, src, parserMode)
+	// If there's no error, return.  If the error is that the source file didn't begin with a
+	// package line and source fragments are ok, fall through to
+	// try as a source fragment.  Stop and return on any other error.
+	if err == nil || !fragmentOk || !strings.Contains(err.Error(), "expected 'package'") {
+		return
+	}
+
+	// If this is a declaration list, make it a source file
+	// by inserting a package clause.
+	// Insert using a ;, not a newline, so that the line numbers
+	// in psrc match the ones in src.
+	psrc := append([]byte("package p;"), src...)
+	file, err = parser.ParseFile(fset, filename, psrc, parserMode)
+	if err == nil {
+		sourceAdj = func(src []byte, indent int) []byte {
+			// Remove the package clause.
+			// Gofmt has turned the ; into a \n.
+			src = src[indent+len("package p\n"):]
+			return bytes.TrimSpace(src)
+		}
+		return
+	}
+	// If the error is that the source file didn't begin with a
+	// declaration, fall through to try as a statement list.
+	// Stop and return on any other error.
+	if !strings.Contains(err.Error(), "expected declaration") {
+		return
+	}
+
+	// If this is a statement list, make it a source file
+	// by inserting a package clause and turning the list
+	// into a function body.  This handles expressions too.
+	// Insert using a ;, not a newline, so that the line numbers
+	// in fsrc match the ones in src.
+	fsrc := append(append([]byte("package p; func _() {"), src...), '\n', '}')
+	file, err = parser.ParseFile(fset, filename, fsrc, parserMode)
+	if err == nil {
+		sourceAdj = func(src []byte, indent int) []byte {
+			// Cap adjusted indent to zero.
+			if indent < 0 {
+				indent = 0
+			}
+			// Remove the wrapping.
+			// Gofmt has turned the ; into a \n\n.
+			// There will be two non-blank lines with indent, hence 2*indent.
+			src = src[2*indent+len("package p\n\nfunc _() {"):]
+			src = src[:len(src)-(indent+len("\n}\n"))]
+			return bytes.TrimSpace(src)
+		}
+		// Gofmt has also indented the function body one level.
+		// Adjust that with indentAdj.
+		indentAdj = -1
+	}
+
+	// Succeeded, or out of options.
+	return
+}
+
+// format formats the given package file originally obtained from src
+// and adjusts the result based on the original source via sourceAdj
+// and indentAdj.
+func format(
+	fset *token.FileSet,
+	file *ast.File,
+	sourceAdj func(src []byte, indent int) []byte,
+	indentAdj int,
+	src []byte,
+	cfg printer.Config,
+) ([]byte, error) {
+	if sourceAdj == nil {
+		// Complete source file.
+		var buf bytes.Buffer
+		err := cfg.Fprint(&buf, fset, file)
+		if err != nil {
+			return nil, err
+		}
+		return buf.Bytes(), nil
+	}
+
+	// Partial source file.
+	// Determine and prepend leading space.
+	i, j := 0, 0
+	for j < len(src) && isSpace(src[j]) {
+		if src[j] == '\n' {
+			i = j + 1 // byte offset of last line in leading space
+		}
+		j++
+	}
+	var res []byte
+	res = append(res, src[:i]...)
+
+	// Determine and prepend indentation of first code line.
+	// Spaces are ignored unless there are no tabs,
+	// in which case spaces count as one tab.
+	indent := 0
+	hasSpace := false
+	for _, b := range src[i:j] {
+		switch b {
+		case ' ':
+			hasSpace = true
+		case '\t':
+			indent++
+		}
+	}
+	if indent == 0 && hasSpace {
+		indent = 1
+	}
+	for i := 0; i < indent; i++ {
+		res = append(res, '\t')
+	}
+
+	// Format the source.
+	// Write it without any leading and trailing space.
+	cfg.Indent = indent + indentAdj
+	var buf bytes.Buffer
+	err := cfg.Fprint(&buf, fset, file)
+	if err != nil {
+		return nil, err
+	}
+	res = append(res, sourceAdj(buf.Bytes(), cfg.Indent)...)
+
+	// Determine and append trailing space.
+	i = len(src)
+	for i > 0 && isSpace(src[i-1]) {
+		i--
+	}
+	return append(res, src[i:]...), nil
+}
+
+func isSpace(b byte) bool {
+	return b == ' ' || b == '\t' || b == '\n' || b == '\r'
+}