[dev.typealias] cmd/compile: recognize type aliases but complain for now (not yet supported)

Added test file.

For #18130.

Change-Id: Ifcfd7cd1acf9dd6a2f4f3d85979d232bb6b8c6b1
Reviewed-on: https://go-review.googlesource.com/34988
Run-TryBot: Robert Griesemer <gri@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

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

@@ -185,6 +185,10 @@ func (p *noder) constDecl(decl *syntax.ConstDecl) []*Node {
 }
 
 func (p *noder) typeDecl(decl *syntax.TypeDecl) *Node {
+	if decl.Alias {
+		yyerror("type alias declarations unimplemented")
+	}
+
 	name := typedcl0(p.name(decl.Name))
 	name.Name.Param.Pragma = Pragma(decl.Pragma)
 

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

@@ -74,6 +74,7 @@ type (
 	// Name Type
 	TypeDecl struct {
 		Name   *Name
+		Alias  bool
 		Type   Expr
 		Group  *Group // nil means not part of a group
 		Pragma Pragma

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

@@ -325,7 +325,7 @@ func (p *parser) constDecl(group *Group) Decl {
 	return d
 }
 
-// TypeSpec = identifier Type .
+// TypeSpec = identifier [ "=" ] Type .
 func (p *parser) typeDecl(group *Group) Decl {
 	if trace {
 		defer p.trace("typeDecl")()
@@ -335,6 +335,7 @@ func (p *parser) typeDecl(group *Group) Decl {
 	d.init(p)
 
 	d.Name = p.name()
+	d.Alias = p.got(_Assign)
 	d.Type = p.tryType()
 	if d.Type == nil {
 		p.syntax_error("in type declaration")

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

@@ -619,7 +619,11 @@ func (p *printer) printRawNode(n Node) {
 		if n.Group == nil {
 			p.print(_Type, blank)
 		}
-		p.print(n.Name, blank, n.Type)
+		p.print(n.Name, blank)
+		if n.Alias {
+			p.print(_Assign, blank)
+		}
+		p.print(n.Type)
 
 	case *VarDecl:
 		if n.Group == nil {

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

@@ -22,3 +22,20 @@ func TestPrint(t *testing.T) {
 	Fprint(os.Stdout, ast, true)
 	fmt.Println()
 }
+
+func TestPrintString(t *testing.T) {
+	for _, want := range []string{
+		"package p",
+		"package p; type _ = int; type T1 = struct{}; type ( _ = *struct{}; T2 = float32 )",
+		// TODO(gri) expand
+	} {
+		ast, err := ParseBytes([]byte(want), nil, nil, 0)
+		if err != nil {
+			t.Error(err)
+			continue
+		}
+		if got := String(ast); got != want {
+			t.Errorf("%q: got %q", want, got)
+		}
+	}
+}

test/alias2.go

+// errorcheck
+
+// Copyright 2016 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.
+
+// Test basic restrictions on type aliases.
+
+// The compiler doesn't implement type aliases yet,
+// so for now we get the same error (unimplemented)
+// everywhere, OR-ed into the ERROR checks.
+// TODO(gri) remove the need for "unimplemented"
+
+package p
+
+import (
+	"reflect"
+	. "reflect"
+)
+
+// Valid type alias declarations.
+
+type _ = int           // ERROR "unimplemented"
+type _ = struct{}      // ERROR "unimplemented"
+type _ = reflect.Value // ERROR "unimplemented"
+type _ = Value         // ERROR "unimplemented"
+
+type (
+	a1 = int           // ERROR "unimplemented"
+	a2 = struct{}      // ERROR "unimplemented"
+	a3 = reflect.Value // ERROR "unimplemented"
+	a4 = Value         // ERROR "unimplemented"
+)
+
+func _() {
+	type _ = int           // ERROR "unimplemented"
+	type _ = struct{}      // ERROR "unimplemented"
+	type _ = reflect.Value // ERROR "unimplemented"
+	type _ = Value         // ERROR "unimplemented"
+
+	type (
+		a1 = int           // ERROR "unimplemented"
+		a2 = struct{}      // ERROR "unimplemented"
+		a3 = reflect.Value // ERROR "unimplemented"
+		a4 = Value         // ERROR "unimplemented"
+	)
+}
+
+// Invalid type alias declarations.
+
+type _ = reflect.ValueOf // ERROR "reflect.ValueOf is not a type|unimplemented"
+
+type b1 = struct{} // ERROR "unimplemented"
+func (b1) m()      {} // disabled ERROR "invalid receiver type"
+
+// TODO(gri) expand
+// It appears that type-checking exits after some more severe errors, so we may
+// need more test files.