go/types: embedded fields can be predeclared types

R=adonovan, r
CC=golang-dev
https://golang.org/cl/7376055

src/pkg/go/types/operand.go

@@ -300,7 +300,11 @@ func lookupFieldBreadthFirst(list []embeddedType, name QualifiedName) (res looku
 					// this level, f.Type appears multiple times at the next
 					// level.
 					if f.IsAnonymous && res.mode == invalid {
-						next = append(next, embeddedType{deref(f.Type).(*NamedType), e.multiples})
+						// Ignore embedded basic types - only user-defined
+						// named types can have methods or have struct fields.
+						if t, _ := deref(f.Type).(*NamedType); t != nil {
+							next = append(next, embeddedType{t, e.multiples})
+						}
 					}
 				}
 
@@ -377,7 +381,11 @@ func lookupField(typ Type, name QualifiedName) lookupResult {
 				// Possible optimization: If the embedded type
 				// is a pointer to the current type we could
 				// ignore it.
-				next = append(next, embeddedType{typ: deref(f.Type).(*NamedType)})
+				// Ignore embedded basic types - only user-defined
+				// named types can have methods or have struct fields.
+				if t, _ := deref(f.Type).(*NamedType); t != nil {
+					next = append(next, embeddedType{typ: t})
+				}
 			}
 		}
 		if len(next) > 0 {

src/pkg/go/types/testdata/decls3.src

@@ -44,6 +44,28 @@ func issue4355() {
 	_ = t /* ERROR "no single field or method" */ .X
 }
 
+// Embedded fields can be predeclared types.
+
+func _() {
+	type T0 struct{
+		int
+		float32
+		f int
+	}
+	var x T0
+	_ = x.int
+	_ = x.float32
+	_ = x.f
+
+	type T1 struct{
+		T0
+	}
+	var y T1
+	_ = y.int
+	_ = y.float32
+	_ = y.f
+}
+
 // Borrowed from the FieldByName test cases in reflect/all_test.go.
 
 type D1 struct {