Ensure foreign window can be reparented out of contained window again

A foreign window embedded into a Qt hierarchy must also support
being removed from that window hierarchy.

Pick-to: 6.6
Change-Id: Id4d08079ff19d67a8989937bc72602e8bd14b31b
Reviewed-by: Richard Moe Gustavsen <richard.gustavsen@qt.io>

src/plugins/platforms/cocoa/qcocoawindow.mm

@@ -1499,6 +1499,10 @@ void QCocoaWindow::recreateWindowIfNeeded()
     QPlatformWindow *parentWindow = QPlatformWindow::parent();
     auto *parentCocoaWindow = static_cast<QCocoaWindow *>(parentWindow);
 
+    QCocoaWindow *oldParentCocoaWindow = nullptr;
+    if (QNSView *qnsView = qnsview_cast(m_view.superview))
+        oldParentCocoaWindow = qnsView.platformWindow;
+
     if (isForeignWindow()) {
         // A foreign window is created as such, and can never move between being
         // foreign and not, so we don't need to get rid of any existing NSWindows,
@@ -1508,6 +1512,8 @@ void QCocoaWindow::recreateWindowIfNeeded()
         // We do however need to manage the parent relationship
         if (parentCocoaWindow)
             [parentCocoaWindow->m_view addSubview:m_view];
+        else if (oldParentCocoaWindow)
+            [m_view removeFromSuperview];
 
         return;
     }
@@ -1515,10 +1521,6 @@ void QCocoaWindow::recreateWindowIfNeeded()
     const bool isEmbeddedView = isEmbedded();
     RecreationReasons recreateReason = RecreationNotNeeded;
 
-    QCocoaWindow *oldParentCocoaWindow = nullptr;
-    if (QNSView *qnsView = qnsview_cast(m_view.superview))
-        oldParentCocoaWindow = qnsView.platformWindow;
-
     if (parentWindow != oldParentCocoaWindow)
          recreateReason |= ParentChanged;
 

src/plugins/platforms/ios/qioswindow.mm

@@ -266,10 +266,16 @@ void QIOSWindow::setWindowState(Qt::WindowStates state)
 
 void QIOSWindow::setParent(const QPlatformWindow *parentWindow)
 {
-    UIView *parentView = parentWindow ? reinterpret_cast<UIView *>(parentWindow->winId())
-        : isQtApplication() ? static_cast<QIOSScreen *>(screen())->uiWindow().rootViewController.view : 0;
+    UIView *parentView = parentWindow ?
+        reinterpret_cast<UIView *>(parentWindow->winId())
+        : isQtApplication() && !isForeignWindow() ?
+            static_cast<QIOSScreen *>(screen())->uiWindow().rootViewController.view
+            : nullptr;
 
-    [parentView addSubview:m_view];
+    if (parentView)
+        [parentView addSubview:m_view];
+    else if (quiview_cast(m_view.superview))
+        [m_view removeFromSuperview];
 }
 
 void QIOSWindow::requestActivateWindow()

tests/auto/gui/kernel/qwindow/tst_foreignwindow.cpp

@@ -81,10 +81,17 @@ void tst_ForeignWindow::embedForeignWindow()
     NativeWindow nativeWindow;
     QVERIFY(nativeWindow);
 
+    // Top level windows may not have 0 as their winId, e.g. on
+    // XCB the root window of the screen is used.
+    const auto originalParentWinId = nativeWindow.parentWinId();
+
     // As a prerequisite to that, we must be able to reparent the foreign window
     std::unique_ptr<QWindow> foreignWindow(QWindow::fromWinId(nativeWindow));
-    foreignWindow.release()->setParent(&parentWindow);
+    foreignWindow->setParent(&parentWindow);
     QTRY_COMPARE(nativeWindow.parentWinId(), parentWindow.winId());
+
+    foreignWindow->setParent(nullptr);
+    QTRY_COMPARE(nativeWindow.parentWinId(), originalParentWinId);
 }
 
 #include <tst_foreignwindow.moc>