Make ObjectByName work with Go types too.

Fixes go-qml#91.

Author: niemeyer

datatype.go

@@ -153,11 +153,15 @@ func unpackDataValue(dvalue *C.DataValue, engine *Engine) interface{} {
 		var c uint32 = *(*uint32)(datap)
 		return color.RGBA{byte(c >> 16), byte(c >> 8), byte(c), byte(c >> 24)}
 	case C.DTGoAddr:
-		return (*(**valueFold)(datap)).gvalue
+		// ObjectByName also does this fold conversion, to have access
+		// to the cvalue. Perhaps the fold should be returned.
+		fold := (*(**valueFold)(datap))
+		ensureEngine(engine.addr, unsafe.Pointer(fold))
+		return fold.gvalue
 	case C.DTInvalid:
 		return nil
 	case C.DTObject:
-		// TODO Would be good to preserve identity on the Go side. See ensureEngine as well.
+		// TODO Would be good to preserve identity on the Go side. See initGoType as well.
 		obj := &Common{
 			engine: engine,
 			addr:   *(*unsafe.Pointer)(datap),

qml.go

@@ -639,13 +639,21 @@ func (obj *Common) Map(property string) *Map {
 func (obj *Common) ObjectByName(objectName string) Object {
 	cname, cnamelen := unsafeStringData(objectName)
 	var dvalue C.DataValue
+	var object Object
 	RunMain(func() {
 		qname := C.newString(cname, cnamelen)
 		defer C.delString(qname)
 		C.objectFindChild(obj.addr, qname, &dvalue)
+		value := unpackDataValue(&dvalue, obj.engine)
+		if dvalue.dataType == C.DTGoAddr {
+			datap := unsafe.Pointer(&dvalue.data)
+			fold := (*(**valueFold)(datap))
+			object = &Common{fold.cvalue, obj.engine}
+		} else {
+			object, _ = value.(Object)
+		}
 	})
-	object, ok := unpackDataValue(&dvalue, obj.engine).(Object)
-	if !ok {
+	if object == nil {
 		panic(fmt.Sprintf("cannot find descendant with objectName == %q", objectName))
 	}
 	return object

qml_test.go

@@ -595,14 +595,23 @@ var tests = []struct {
 		QMLLog: "Identical: true",
 	},
 	{
-		Summary: "Object finding via objectName",
+		Summary: "Object finding via ObjectByName",
 		QML:     `Item { Item { objectName: "subitem"; property string s: "<found>" } }`,
 		Done: func(c *TestData) {
 			obj := c.root.ObjectByName("subitem")
 			c.Check(obj.String("s"), Equals, "<found>")
 			c.Check(func() { c.root.ObjectByName("foo") }, Panics, `cannot find descendant with objectName == "foo"`)
 		},
 	},
+	{
+		Summary: "Object finding via ObjectByName on GoType",
+		QML:     `Item { GoType { objectName: "subitem"; property string s: "<found>" } }`,
+		Done: func(c *TestData) {
+			obj := c.root.ObjectByName("subitem")
+			c.Check(obj.String("s"), Equals, "<found>")
+			c.Check(func() { c.root.ObjectByName("foo") }, Panics, `cannot find descendant with objectName == "foo"`)
+		},
+	},
 	{
 		Summary: "Register Go type",
 		QML:     `GoType { objectName: "test"; Component.onCompleted: console.log("String is", stringValue) }`,