Fix separate delete of window and windowcontainer

The documentation says we can change window parent to avoid the widget
deleting the window. That didn't work as the widget didn't get the
child-removed event as it wasn't the parent.

This patch instead uses an event filter on the set parent.

Pick-to: 6.3 6.2
Change-Id: I1f61d1832fcf3257722f305beeefd8f1abf1f656
Reviewed-by: Laszlo Agocs <laszlo.agocs@qt.io>

src/widgets/kernel/qwindowcontainer.cpp

@@ -191,6 +191,7 @@ QWindowContainer::QWindowContainer(QWindow *embeddedWindow, QWidget *parent, Qt:
     d->fakeParent.setObjectName(windowName + "ContainerFakeParent"_L1);
 
     d->window->setParent(&d->fakeParent);
+    d->window->parent()->installEventFilter(this);
     d->window->setFlag(Qt::SubWindow);
 
     setAcceptDrops(true);
@@ -239,6 +240,26 @@ void QWindowContainer::focusWindowChanged(QWindow *focusWindow)
     }
 }
 
+/*!
+    \internal
+ */
+
+bool QWindowContainer::eventFilter(QObject *o, QEvent *e)
+{
+    Q_D(QWindowContainer);
+    if (!d->window)
+        return false;
+
+    if (e->type() == QEvent::ChildRemoved) {
+        QChildEvent *ce = static_cast<QChildEvent *>(e);
+        if (ce->child() == d->window) {
+            o->removeEventFilter(this);
+            d->window = nullptr;
+        }
+    }
+    return false;
+}
+
 /*!
     \internal
  */
@@ -251,12 +272,6 @@ bool QWindowContainer::event(QEvent *e)
 
     QEvent::Type type = e->type();
     switch (type) {
-    case QEvent::ChildRemoved: {
-        QChildEvent *ce = static_cast<QChildEvent *>(e);
-        if (ce->child() == d->window)
-            d->window = nullptr;
-        break;
-    }
     // The only thing we are interested in is making sure our sizes stay
     // in sync, so do a catch-all case.
     case QEvent::Resize:
@@ -271,10 +286,13 @@ bool QWindowContainer::event(QEvent *e)
     case QEvent::Show:
         d->updateUsesNativeWidgets();
         if (d->isStillAnOrphan()) {
+            d->window->parent()->removeEventFilter(this);
             d->window->setParent(d->usesNativeWidgets
                                  ? windowHandle()
                                  : window()->windowHandle());
             d->fakeParent.destroy();
+            if (d->window->parent())
+                d->window->parent()->installEventFilter(this);
         }
         if (d->window->parent()) {
             d->markParentChain();
@@ -345,7 +363,10 @@ static void qwindowcontainer_traverse(QWidget *parent, qwindowcontainer_traverse
 void QWindowContainer::toplevelAboutToBeDestroyed(QWidget *parent)
 {
     if (QWindowContainerPrivate *d = QWindowContainerPrivate::get(parent)) {
+        if (d->window->parent())
+            d->window->parent()->removeEventFilter(parent);
         d->window->setParent(&d->fakeParent);
+        d->window->parent()->installEventFilter(parent);
     }
     qwindowcontainer_traverse(parent, toplevelAboutToBeDestroyed);
 }
@@ -363,7 +384,9 @@ void QWindowContainer::parentWasChanged(QWidget *parent)
                 tld->createTLSysExtra();
                 Q_ASSERT(toplevel->windowHandle());
             }
+            d->window->parent()->removeEventFilter(parent);
             d->window->setParent(toplevel->windowHandle());
+            toplevel->windowHandle()->installEventFilter(parent);
             d->fakeParent.destroy();
             d->updateGeometry();
         }

src/widgets/kernel/qwindowcontainer_p.h

@@ -40,6 +40,7 @@ public:
 
 protected:
     bool event(QEvent *ev) override;
+    bool eventFilter(QObject *, QEvent *ev) override;
 
 private slots:
     void focusWindowChanged(QWindow *focusWindow);

tests/auto/widgets/kernel/qwindowcontainer/tst_qwindowcontainer.cpp

@@ -50,6 +50,7 @@ private slots:
     void testOwnership();
     void testBehindTheScenesDeletion();
     void testUnparenting();
+    void testReparenting();
     void testUnparentReparent();
     void testActivation();
     void testAncestorChange();
@@ -206,12 +207,12 @@ void tst_QWindowContainer::testActivation()
 
 void tst_QWindowContainer::testUnparenting()
 {
-    QWindow *window = new QWindow();
+    QPointer<QWindow> window(new QWindow());
     QScopedPointer<QWidget> container(QWidget::createWindowContainer(window));
     container->setWindowTitle(QTest::currentTestFunction());
     container->setGeometry(m_availableGeometry.x() + 100, m_availableGeometry.y() + 100, 200, 100);
 
-    window->setParent(0);
+    window->setParent(nullptr);
 
     container->show();
 
@@ -219,6 +220,26 @@ void tst_QWindowContainer::testUnparenting()
 
     // Window should not be made visible by container..
     QVERIFY(!window->isVisible());
+
+    container.reset();
+    QVERIFY(window);
+    delete window;
+}
+
+void tst_QWindowContainer::testReparenting()
+{
+    QPointer<QWindow> window1(new QWindow());
+    QScopedPointer<QWindow> window2(new QWindow());
+    QScopedPointer<QWidget> container(QWidget::createWindowContainer(window1));
+
+    window1->setParent(window2.data());
+
+    // Not deleted with container
+    container.reset();
+    QVERIFY(window1);
+    // but deleted with new parent
+    window2.reset();
+    QVERIFY(!window1);
 }
 
 void tst_QWindowContainer::testUnparentReparent()