go/parser: unify parsing of const and var declarations

The AST representation is already identical. Making the
code (nearly) identical in the parser reduces code size
and ensures that the ast.ValueSpec nodes have the same
values (specifically, iota). This in turn permits the
sharing of much of the respective code in the typechecker.

While at it: type functions work now, so use them.

R=r
CC=golang-dev
https://golang.org/cl/6624047

src/pkg/go/parser/parser.go

@@ -2040,7 +2040,7 @@ func (p *parser) parseStmt() (s ast.Stmt) {
 // ----------------------------------------------------------------------------
 // Declarations
 
-type parseSpecFunction func(p *parser, doc *ast.CommentGroup, iota int) ast.Spec
+type parseSpecFunction func(p *parser, doc *ast.CommentGroup, keyword token.Token, iota int) ast.Spec
 
 func isValidImport(lit string) bool {
 	const illegalChars = `!"#$%&'()*,:;<=>?[\]^{|}` + "`\uFFFD"
@@ -2053,7 +2053,7 @@ func isValidImport(lit string) bool {
 	return s != ""
 }
 
-func parseImportSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+func (p *parser) parseImportSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
 	if p.trace {
 		defer un(trace(p, "ImportSpec"))
 	}
@@ -2091,15 +2091,15 @@ func parseImportSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
 	return spec
 }
 
-func parseConstSpec(p *parser, doc *ast.CommentGroup, iota int) ast.Spec {
+func (p *parser) parseValueSpec(doc *ast.CommentGroup, keyword token.Token, iota int) ast.Spec {
 	if p.trace {
-		defer un(trace(p, "ConstSpec"))
+		defer un(trace(p, keyword.String()+"Spec"))
 	}
 
 	idents := p.parseIdentList()
 	typ := p.tryType()
 	var values []ast.Expr
-	if typ != nil || p.tok == token.ASSIGN || iota == 0 {
+	if p.tok == token.ASSIGN || keyword == token.CONST && (typ != nil || iota == 0) || keyword == token.VAR && typ == nil {
 		p.expect(token.ASSIGN)
 		values = p.parseRhsList()
 	}
@@ -2121,7 +2121,7 @@ func parseConstSpec(p *parser, doc *ast.CommentGroup, iota int) ast.Spec {
 	return spec
 }
 
-func parseTypeSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
+func (p *parser) parseTypeSpec(doc *ast.CommentGroup, _ token.Token, _ int) ast.Spec {
 	if p.trace {
 		defer un(trace(p, "TypeSpec"))
 	}
@@ -2142,36 +2142,6 @@ func parseTypeSpec(p *parser, doc *ast.CommentGroup, _ int) ast.Spec {
 	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:     doc,
-		Names:   idents,
-		Type:    typ,
-		Values:  values,
-		Comment: 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()+")"))
@@ -2185,12 +2155,12 @@ func (p *parser) parseGenDecl(keyword token.Token, f parseSpecFunction) *ast.Gen
 		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))
+			list = append(list, f(p, p.leadComment, keyword, iota))
 		}
 		rparen = p.expect(token.RPAREN)
 		p.expectSemi()
 	} else {
-		list = append(list, f(p, nil, 0))
+		list = append(list, f(p, nil, keyword, 0))
 	}
 
 	return &ast.GenDecl{
@@ -2290,14 +2260,11 @@ func (p *parser) parseDecl(sync func(*parser)) ast.Decl {
 
 	var f parseSpecFunction
 	switch p.tok {
-	case token.CONST:
+	case token.CONST, token.VAR:
-		f = parseConstSpec
+		f = (*parser).parseValueSpec
 
 	case token.TYPE:
-		f = parseTypeSpec
+		f = (*parser).parseTypeSpec
-
-	case token.VAR:
-		f = parseVarSpec
 
 	case token.FUNC:
 		return p.parseFuncDecl()
@@ -2349,7 +2316,7 @@ func (p *parser) parseFile() *ast.File {
 	if p.mode&PackageClauseOnly == 0 {
 		// import decls
 		for p.tok == token.IMPORT {
-			decls = append(decls, p.parseGenDecl(token.IMPORT, parseImportSpec))
+			decls = append(decls, p.parseGenDecl(token.IMPORT, (*parser).parseImportSpec))
 		}
 
 		if p.mode&ImportsOnly == 0 {