go/types: Permit dereferencing of named pointer types.

R=golang-dev, gri
CC=golang-dev
https://golang.org/cl/7358044

src/pkg/go/types/expr.go

@@ -1193,7 +1193,7 @@ func (check *checker) rawExpr(x *operand, e ast.Expr, hint Type, iota int, cycle
 		case typexpr:
 			x.typ = &Pointer{Base: x.typ}
 		default:
-			if typ, ok := x.typ.(*Pointer); ok {
+			if typ, ok := underlying(x.typ).(*Pointer); ok {
 				x.mode = variable
 				x.typ = typ.Base
 			} else {

src/pkg/go/types/testdata/expr0.src

@@ -149,3 +149,13 @@ var (
 	_ = &((((T{1, 2}))))
 	_ = &f /* ERROR "cannot take address" */ ()
 )
+
+// recursive pointer types
+type P *P
+
+var (
+	p1 P = new(P)
+	p2 P = *p1
+	p3 P = &p2
+)
+