go/parser: test and fix := scoping bug

R=iant
CC=golang-dev, gri
https://golang.org/cl/5327048

src/pkg/go/parser/parser.go

@@ -434,7 +434,9 @@ func (p *parser) parseLhsList() []ast.Expr {
 	switch p.tok {
 	case token.DEFINE:
 		// lhs of a short variable declaration
-		p.shortVarDecl(p.makeIdentList(list))
+		// but doesn't enter scope until later:
+		// caller must call p.shortVarDecl(p.makeIdentList(list))
+		// at appropriate time.
 	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
@@ -1398,6 +1400,9 @@ func (p *parser) parseSimpleStmt(mode int) (ast.Stmt, bool) {
 		} else {
 			y = p.parseRhsList()
 		}
+		if tok == token.DEFINE {
+			p.shortVarDecl(p.makeIdentList(x))
+		}
 		return &ast.AssignStmt{x, pos, tok, y}, isRange
 	}
 
@@ -1722,6 +1727,9 @@ func (p *parser) parseCommClause() *ast.CommClause {
 				}
 				p.next()
 				rhs = p.parseRhs()
+				if tok == token.DEFINE && lhs != nil {
+					p.shortVarDecl(p.makeIdentList(lhs))
+				}
 			} else {
 				// rhs must be single receive operation
 				if len(lhs) > 1 {

src/pkg/go/parser/parser_test.go

@@ -5,6 +5,7 @@
 package parser
 
 import (
+	"go/ast"
 	"go/token"
 	"os"
 	"testing"
@@ -134,3 +135,46 @@ func TestParse4(t *testing.T) {
 		}
 	}
 }
+
+func TestColonEqualsScope(t *testing.T) {
+	f, err := ParseFile(fset, "", `package p; func f() { x, y, z := x, y, z }`, 0)
+	if err != nil {
+		t.Errorf("parse: %s", err)
+	}
+
+	// RHS refers to undefined globals; LHS does not.
+	as := f.Decls[0].(*ast.FuncDecl).Body.List[0].(*ast.AssignStmt)
+	for _, v := range as.Rhs {
+		id := v.(*ast.Ident)
+		if id.Obj != nil {
+			t.Errorf("rhs %s has Obj, should not", id.Name)
+		}
+	}
+	for _, v := range as.Lhs {
+		id := v.(*ast.Ident)
+		if id.Obj == nil {
+			t.Errorf("lhs %s does not have Obj, should", id.Name)
+		}
+	}
+}
+
+func TestVarScope(t *testing.T) {
+	f, err := ParseFile(fset, "", `package p; func f() { var x, y, z = x, y, z }`, 0)
+	if err != nil {
+		t.Errorf("parse: %s", err)
+	}
+
+	// RHS refers to undefined globals; LHS does not.
+	as := f.Decls[0].(*ast.FuncDecl).Body.List[0].(*ast.DeclStmt).Decl.(*ast.GenDecl).Specs[0].(*ast.ValueSpec)
+	for _, v := range as.Values {
+		id := v.(*ast.Ident)
+		if id.Obj != nil {
+			t.Errorf("rhs %s has Obj, should not", id.Name)
+		}
+	}
+	for _, id := range as.Names {
+		if id.Obj == nil {
+			t.Errorf("lhs %s does not have Obj, should", id.Name)
+		}
+	}
+}