7 files changed, 57 insertions, 16 deletions

diff --git a/src/pkg/go/ast/ast.go b/src/pkg/go/ast/ast.go
index 1dfe2a7ea..60a90050c 100644
--- a/src/pkg/go/ast/ast.go
+++ b/src/pkg/go/ast/ast.go
@@ -172,10 +172,16 @@ type (
 		Sel	*Ident;	// field selector
 	};
 
-	// An IndexExpr node represents an expression followed by an index or slice.
+	// An IndexExpr node represents an expression followed by an index.
 	IndexExpr	struct {
 		X	Expr;	// expression
-		Index	Expr;	// index expression or beginning of slice range
+		Index	Expr;	// index expression
+	};
+
+	// An SliceExpr node represents an expression followed by slice indices.
+	SliceExpr	struct {
+		X	Expr;	// expression
+		Index	Expr;	// beginning of slice range
 		End	Expr;	// end of slice range; or nil
 	};
 
@@ -305,6 +311,7 @@ func (x *FuncLit) Pos() token.Position		{ return x.Type.Pos() }
 func (x *CompositeLit) Pos() token.Position	{ return x.Type.Pos() }
 func (x *SelectorExpr) Pos() token.Position	{ return x.X.Pos() }
 func (x *IndexExpr) Pos() token.Position	{ return x.X.Pos() }
+func (x *SliceExpr) Pos() token.Position	{ return x.X.Pos() }
 func (x *TypeAssertExpr) Pos() token.Position	{ return x.X.Pos() }
 func (x *CallExpr) Pos() token.Position		{ return x.Fun.Pos() }
 func (x *BinaryExpr) Pos() token.Position	{ return x.X.Pos() }
@@ -323,6 +330,7 @@ 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()		{}
diff --git a/src/pkg/go/ast/walk.go b/src/pkg/go/ast/walk.go
index c1ed36621..08c399219 100644
--- a/src/pkg/go/ast/walk.go
+++ b/src/pkg/go/ast/walk.go
@@ -129,6 +129,10 @@ func Walk(v Visitor, node interface{}) {
 	case *IndexExpr:
 		Walk(v, n.X);
 		Walk(v, n.Index);
+
+	case *SliceExpr:
+		Walk(v, n.X);
+		Walk(v, n.Index);
 		Walk(v, n.End);
 
 	case *TypeAssertExpr:
diff --git a/src/pkg/go/parser/parser.go b/src/pkg/go/parser/parser.go
index ba91ceb52..1195a24fa 100644
--- a/src/pkg/go/parser/parser.go
+++ b/src/pkg/go/parser/parser.go
@@ -962,23 +962,28 @@ func (p *parser) parseSelectorOrTypeAssertion(x ast.Expr) ast.Expr {
 }
 
 
-func (p *parser) parseIndex(x ast.Expr) ast.Expr {
+func (p *parser) parseIndexOrSlice(x ast.Expr) ast.Expr {
 	if p.trace {
-		defer un(trace(p, "Index"))
+		defer un(trace(p, "IndexOrSlice"))
 	}
 
 	p.expect(token.LBRACK);
 	p.exprLev++;
-	begin := p.parseExpr();
-	var end ast.Expr;
+	index := p.parseExpr();
 	if p.tok == token.COLON {
 		p.next();
-		end = p.parseExpr();
+		var end ast.Expr;
+		if p.tok != token.RBRACK {
+			end = p.parseExpr()
+		}
+		x = &ast.SliceExpr{x, index, end};
+	} else {
+		x = &ast.IndexExpr{x, index}
 	}
 	p.exprLev--;
 	p.expect(token.RBRACK);
 
-	return &ast.IndexExpr{x, begin, end};
+	return x;
 }
 
 
@@ -1072,6 +1077,7 @@ func (p *parser) checkExpr(x ast.Expr) ast.Expr {
 	case *ast.ParenExpr:
 	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
@@ -1168,7 +1174,7 @@ L:	for {
 		case token.PERIOD:
 			x = p.parseSelectorOrTypeAssertion(p.checkExpr(x))
 		case token.LBRACK:
-			x = p.parseIndex(p.checkExpr(x))
+			x = p.parseIndexOrSlice(p.checkExpr(x))
 		case token.LPAREN:
 			x = p.parseCallOrConversion(p.checkExprOrType(x))
 		case token.LBRACE:
diff --git a/src/pkg/go/printer/nodes.go b/src/pkg/go/printer/nodes.go
index 243c168a7..6304830bd 100644
--- a/src/pkg/go/printer/nodes.go
+++ b/src/pkg/go/printer/nodes.go
@@ -665,17 +665,25 @@ func (p *printer) expr1(expr ast.Expr, prec1, depth int, ctxt exprContext, multi
 		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, 0, multiLine);
 		p.print(token.LBRACK);
 		p.expr0(x.Index, depth+1, multiLine);
+		p.print(token.RBRACK);
+
+	case *ast.SliceExpr:
+		// TODO(gri): should treat[] like parentheses and undo one level of depth
+		p.expr1(x.X, token.HighestPrec, 1, 0, multiLine);
+		p.print(token.LBRACK);
+		p.expr0(x.Index, depth+1, multiLine);
+		// blanks around ":" if both sides exist and either side is a binary expression
+		if depth <= 1 && x.End != nil && (isBinary(x.Index) || isBinary(x.End)) {
+			p.print(blank, token.COLON, blank)
+		} else {
+			p.print(token.COLON)
+		}
 		if x.End != nil {
-			// blanks around ":" if either side is a binary expression
-			if depth <= 1 && (isBinary(x.Index) || isBinary(x.End)) {
-				p.print(blank, token.COLON, blank)
-			} else {
-				p.print(token.COLON)
-			}
-			p.expr0(x.End, depth+1, multiLine);
+			p.expr0(x.End, depth+1, multiLine)
 		}
 		p.print(token.RBRACK);
 
diff --git a/src/pkg/go/printer/testdata/expressions.golden b/src/pkg/go/printer/testdata/expressions.golden
index 1d785d91f..0530e81da 100644
--- a/src/pkg/go/printer/testdata/expressions.golden
+++ b/src/pkg/go/printer/testdata/expressions.golden
@@ -53,6 +53,11 @@ func _() {
 	_ = 1 + 2*3;
 	_ = s[1 : 2*3];
 	_ = s[a : b-c];
+	_ = s[0:];
+	_ = s[a+b];
+	_ = 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];
diff --git a/src/pkg/go/printer/testdata/expressions.input b/src/pkg/go/printer/testdata/expressions.input
index 6ccc9a833..decb58196 100644
--- a/src/pkg/go/printer/testdata/expressions.input
+++ b/src/pkg/go/printer/testdata/expressions.input
@@ -53,6 +53,11 @@ func _() {
 	_ = 1 + 2*3;
 	_ = s[1 : 2*3];
 	_ = s[a : b-c];
+	_ = s[0:];
+	_ = s[a+b];
+	_ = 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];
diff --git a/src/pkg/go/printer/testdata/expressions.raw b/src/pkg/go/printer/testdata/expressions.raw
index 55986e2e6..3e4f32648 100644
--- a/src/pkg/go/printer/testdata/expressions.raw
+++ b/src/pkg/go/printer/testdata/expressions.raw
@@ -53,6 +53,11 @@ func _() {
 	_ = 1 + 2*3;
 	_ = s[1 : 2*3];
 	_ = s[a : b-c];
+	_ = s[0:];
+	_ = s[a+b];
+	_ = 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];