Fix visual parent ownership with scenes that create windows

Commit 39540124dd0900e0c99dcda8c0ebdf4f3cea8d5e introduced the concept that
a visual parent marks its children, by recursively marking the children of
the root item in a QQuickView. This allowed for the removal of an ugly hack
in QtQuick Controls.

Unfortunately that fix is incomplete in the sense that it makes the incorrect
assumption that a QQuickView is always used. The use-case in the bug report is
to have child items inside a QtQuick.Window (a regular ApplicationWindow in
fact). That window - implemented by QQuickWindowQmlImpl - also needs to mark
its children, so this patch introduces the use of the same GC marking helper
class (which now operates on a QQuickWindow instead of a QQuickViewPrivate).

Task-number: QTBUG-37711
Change-Id: Id788e84dbb041ac8ba6ff23dc4ef56f6fe9e465a
Reviewed-by: Lars Knoll <lars.knoll@digia.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/src/quick/items/qquickwindowmodule.cpp b/src/quick/items/qquickwindowmodule.cpp
index 3bd62d21db..d06fff8c3e 100644
--- a/src/quick/items/qquickwindowmodule.cpp
+++ b/src/quick/items/qquickwindowmodule.cpp
@@ -41,6 +41,7 @@
 
 #include "qquickwindowmodule_p.h"
 #include "qquickscreen_p.h"
+#include "qquickview_p.h"
 #include <QtQuick/QQuickWindow>
 #include <QtCore/QCoreApplication>
 #include <QtQml/QQmlEngine>
@@ -91,12 +92,19 @@ Q_SIGNALS:
 
 protected:
     void classBegin() {
+        QQmlEngine* e = qmlEngine(this);
         //Give QQuickView behavior when created from QML with QQmlApplicationEngine
         if (QCoreApplication::instance()->property("__qml_using_qqmlapplicationengine") == QVariant(true)) {
-            QQmlEngine* e = qmlEngine(this);
             if (e && !e->incubationController())
                 e->setIncubationController(incubationController());
         }
+        Q_ASSERT(e);
+        {
+            QV4::ExecutionEngine *v4 = QQmlEnginePrivate::getV4Engine(e);
+            QV4::Scope scope(v4);
+            QV4::ScopedObject v(scope, new (v4->memoryManager) QQuickRootItemMarker(e, this));
+            rootItemMarker = v;
+        }
     }
 
     void componentComplete() {
@@ -158,6 +166,7 @@ private:
     bool m_complete;
     bool m_visible;
     Visibility m_visibility;
+    QV4::PersistentValue rootItemMarker;
 };
 
 void QQuickWindowModule::defineModule()