Instantiator: don't interfere with delegates that assign parents

[ChangeLog][QtQml][Instantiator] Instantiator now avoids re-assigning a
delegate object's parent to itself if it was already set; thus, you can
now declare a parent assignment.

Task-number: QTBUG-64546
Task-number: QTBUG-84730
Change-Id: I7d95fa76e71c363b4cb5b7a512c2e984488c8af4
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

examples/quick/pointerhandlers/pointerhandlers.qml

@@ -83,13 +83,10 @@ Rectangle {
         z: 10000
         anchors.fill: parent
 
-        // TODO use Instantiator to create these... but we need to be able to set their parents to glassPane somehow (QTBUG-64546)
+        Instantiator {
-        TouchpointFeedbackSprite { }
+            model: 10
-        TouchpointFeedbackSprite { }
+            delegate: TouchpointFeedbackSprite { parent: glassPane }
-        TouchpointFeedbackSprite { }
+        }
-        TouchpointFeedbackSprite { }
-        TouchpointFeedbackSprite { }
-        TouchpointFeedbackSprite { }
 
         MouseFeedbackSprite { }
     }

src/qmlmodels/qqmlinstantiator.cpp

@@ -128,6 +128,7 @@ void QQmlInstantiatorPrivate::_q_createdItem(int idx, QObject* item)
         return;
     if (requestedIndex != idx) // Asynchronous creation, reference the object
         (void)instanceModel->object(idx);
+    if (!item->parent())
         item->setParent(q);
     if (objects.size() < idx + 1) {
         int modelCount = instanceModel->count();

tests/auto/qml/qqmlinstantiator/data/handlerWithParent.qml

@@ -0,0 +1,12 @@
+import QtQuick
+
+Item {
+    id: root
+    Instantiator {
+        model: 2
+        delegate: PointHandler {
+            objectName: "pointHandler"
+            parent: root
+        }
+    }
+}

tests/auto/qml/qqmlinstantiator/tst_qqmlinstantiator.cpp

@@ -56,6 +56,8 @@ private slots:
 
     void asynchronous_data();
     void asynchronous();
+
+    void handlerWithParent();
 };
 
 tst_qqmlinstantiator::tst_qqmlinstantiator()
@@ -276,6 +278,19 @@ void tst_qqmlinstantiator::asynchronous()
     }
 }
 
+void tst_qqmlinstantiator::handlerWithParent()
+{
+    QQmlEngine engine;
+    QQmlComponent component(&engine, testFileUrl("handlerWithParent.qml"));
+    QObject *rootObject = component.create();
+    QVERIFY(rootObject != nullptr);
+    const auto handlers = rootObject->findChildren<QObject *>("pointHandler");
+    QCOMPARE(handlers.count(), 2);
+    for (const auto *h : handlers) {
+        QCOMPARE(h->parent(), rootObject);
+    }
+}
+
 QTEST_MAIN(tst_qqmlinstantiator)
 
 #include "tst_qqmlinstantiator.moc"