reflect: unpack interfaces in MapKeys() if needed

src/reflect/value.go

@@ -779,8 +779,17 @@ func (v Value) MapKeys() []Value {
 	k := New(v.typecode.Key())
 	e := New(v.typecode.Elem())
 
+	keyType := v.typecode.Key().(*rawType)
+	isKeyStoredAsInterface := keyType.Kind() != String && !keyType.isBinary()
+
 	for hashmapNext(v.pointer(), it, k.value, e.value) {
-		keys = append(keys, k.Elem())
+		if isKeyStoredAsInterface {
+			intf := *(*interface{})(k.value)
+			v := ValueOf(intf)
+			keys = append(keys, v)
+		} else {
+			keys = append(keys, k.Elem())
+		}
 		k = New(v.typecode.Key())
 	}
 

src/reflect/value_test.go

@@ -134,6 +134,20 @@ func TestTinyMap(t *testing.T) {
 		t.Errorf("m[hello, 4]=%v, want 6", six)
 	}
 
+	keys := refsimap.MapKeys()
+	if len(keys) != 1 {
+		t.Errorf("refsimap: MapKeys()=%v, want 1", len(keys))
+	}
+	if keys[0].Type() != TypeOf(stringint{}) {
+		t.Errorf("keys[0] has wrong type: %v", keys[0].Type().String())
+	}
+
+	sikey := keys[0].Interface().(stringint)
+
+	if sikey != (stringint{"hello", 4}) {
+		t.Errorf("sikey has unexpected value: %#v", sikey)
+	}
+
 	// make sure we can look up interface keys with reflection
 	type unmarshalerText struct {
 		A, B string