cmd/compile: simplify parsing of type aliases

Change-Id: Ia86841cf84bc17ff6ecc6e5ac4cec86384a0da00
Reviewed-on: https://go-review.googlesource.com/31719Reviewed-by: Matthew Dempsky <mdempsky@google.com>

src/cmd/compile/internal/gc/noder.go

@@ -90,11 +90,6 @@ func (p *noder) decls(decls []syntax.Decl) (l []*Node) {
 			lastConstGroup = decl.Group
 
 		case *syntax.TypeDecl:
-			// TODO(gri) remove this notation - we're not going to use it after all
-			if decl.Alias {
-				yyerror("type aliases using = not supported")
-				break
-			}
 			l = append(l, p.typeDecl(decl))
 
 		case *syntax.FuncDecl:

src/cmd/compile/internal/syntax/nodes.go

@@ -89,7 +89,6 @@ type (
 	TypeDecl struct {
 		Name   *Name
 		Type   Expr
-		Alias  bool
 		Group  *Group // nil means not part of a group
 		Pragma Pragma
 		decl

src/cmd/compile/internal/syntax/parser.go

@@ -322,7 +322,8 @@ func (p *parser) aliasDecl(tok token, name *Name, group *Group) Decl {
 	d := new(AliasDecl)
 	d.initFrom(&name.node)
 
-	p.want(_Rarrow)
+	// lhs identifier and "=>" have been consumed already
+
 	d.Tok = tok
 	d.Name = name
 	d.Orig = p.dotname(p.name())
@@ -338,7 +339,7 @@ func (p *parser) constDecl(group *Group) Decl {
 	}
 
 	name := p.name()
-	if p.tok == _Rarrow {
+	if p.got(_Rarrow) {
 		return p.aliasDecl(Const, name, group)
 	}
 
@@ -364,7 +365,8 @@ func (p *parser) typeDecl(group *Group) Decl {
 	}
 
 	name := p.name()
-	if p.tok == _Rarrow {
+	// permit both: type T => p.T and: type T = p.T for now
+	if p.got(_Rarrow) || p.got(_Assign) {
 		return p.aliasDecl(Type, name, group)
 	}
 
@@ -372,9 +374,6 @@ func (p *parser) typeDecl(group *Group) Decl {
 	d.initFrom(&name.node)
 
 	d.Name = name
-	// accept "type T = p.T" for now so we can experiment
-	// with a type-alias only approach as well
-	d.Alias = p.got(_Assign)
 	d.Type = p.tryType()
 	if d.Type == nil {
 		p.syntax_error("in type declaration")
@@ -393,7 +392,7 @@ func (p *parser) varDecl(group *Group) Decl {
 	}
 
 	name := p.name()
-	if p.tok == _Rarrow {
+	if p.got(_Rarrow) {
 		return p.aliasDecl(Var, name, group)
 	}
 
@@ -449,7 +448,7 @@ func (p *parser) funcDecl() Decl {
 	}
 
 	name := p.name()
-	if recv == nil && p.tok == _Rarrow {
+	if recv == nil && p.got(_Rarrow) {
 		return p.aliasDecl(Func, name, nil)
 	}
 

src/cmd/compile/internal/syntax/printer.go

@@ -625,11 +625,7 @@ func (p *printer) printRawNode(n Node) {
 		if n.Group == nil {
 			p.print(_Type, blank)
 		}
-		p.print(n.Name, blank)
-		if n.Alias {
-			p.print(_Assign, blank)
-		}
-		p.print(n.Type)
+		p.print(n.Name, blank, n.Type)
 
 	case *VarDecl:
 		if n.Group == nil {