Widgets: setTransientParent() when a QMenu is a window

On some platforms, such as X11 and Wayland with some compositors,
QMenu could be a popup window, which should be set a transient parent
to get relative position, which is requested by Wayland.

Added transientParentWindow() for QMenuPrivate like QDialogPrivate.

Fixes: QTBUG-68636
Pick-to: 6.2
Change-Id: I6d8880cb008ecf61a4c005898b38e3953379a13d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/widgets/widgets/qmenu.cpp

@@ -625,6 +625,29 @@ void QMenuPrivate::hideMenu(QMenu *menu)
     menu->d_func()->causedPopup.widget = nullptr;
 }
 
+QWindow *QMenuPrivate::transientParentWindow() const
+{
+    Q_Q(const QMenu);
+    if (const QWidget *parent = q->nativeParentWidget()) {
+        if (parent->windowHandle())
+            return parent->windowHandle();
+    }
+
+    if (const QWindow *w = q->windowHandle()) {
+        if (w->transientParent())
+            return w->transientParent();
+    }
+
+    if (causedPopup.widget) {
+        if (const QWidget *w = causedPopup.widget.data()) {
+            if (const QWidget *ww = w->window())
+                return ww->windowHandle();
+        }
+    }
+
+    return nullptr;
+}
+
 void QMenuPrivate::popupAction(QAction *action, int delay, bool activateFirst)
 {
     Q_Q(QMenu);
@@ -2983,6 +3006,8 @@ bool QMenu::event(QEvent *e)
         d->sloppyState.reset();
         if (d->currentAction)
             d->popupAction(d->currentAction, 0, false);
+        if (isWindow() && window() && window()->windowHandle() && !window()->windowHandle()->transientParent())
+            window()->windowHandle()->setTransientParent(d->transientParentWindow());
         break;
 #if QT_CONFIG(tooltip)
     case QEvent::ToolTip:

src/widgets/widgets/qmenu_p.h

@@ -440,6 +440,7 @@ public:
     QMenuCaused causedPopup;
     void hideUpToMenuBar();
     void hideMenu(QMenu *menu);
+    QWindow *transientParentWindow() const;
 
     //index mappings
     inline QAction *actionAt(int i) const { return q_func()->actions().at(i); }

tests/auto/widgets/widgets/qmenu/tst_qmenu.cpp

@@ -118,6 +118,7 @@ private slots:
     void QTBUG_89082_actionTipsHide();
     void QTBUG8122_widgetActionCrashOnClose();
     void widgetActionTriggerClosesMenu();
+    void transientParent();
 
     void QTBUG_10735_crashWithDialog();
 #ifdef Q_OS_MAC
@@ -1588,6 +1589,54 @@ void tst_QMenu::widgetActionTriggerClosesMenu()
     QCOMPARE(actionTriggered, &widgetAction);
 }
 
+void tst_QMenu::transientParent()
+{
+    QMainWindow window;
+    window.resize(480, 320);
+    window.menuBar()->setNativeMenuBar(false);
+    centerOnScreen(&window);
+
+    QMenu *fileMenu = new QMenu("&File");
+    QAction *exitAct = new QAction("Exit");
+    fileMenu->addAction(exitAct);
+
+    QMenu *editMenu = new QMenu("&Edit");
+    QAction *undoAct = new QAction("Undo");
+    editMenu->addAction(undoAct);
+
+    QMenuBar *menuBar = new QMenuBar;
+    menuBar->addMenu(fileMenu);
+    menuBar->addMenu(editMenu);
+    window.setMenuBar(menuBar);
+
+    // On Mac, we need to create native key events to test menu
+    // action activation, so skip this part of the test.
+#if QT_CONFIG(shortcut) && !defined(Q_OS_DARWIN)
+    window.show();
+    QVERIFY(QTest::qWaitForWindowActive(&window));
+    QWindow *topLevel = window.windowHandle();
+    QVERIFY(topLevel);
+
+    QApplication::setActiveWindow(&window);
+    window.setFocus();
+    QVERIFY(QTest::qWaitForWindowActive(&window));
+    QVERIFY(window.hasFocus());
+
+    QTest::keyPress(&window, Qt::Key_F, Qt::AltModifier);
+    QTRY_VERIFY(QTest::qWaitForWindowExposed(fileMenu));
+    if (fileMenu->isWindow() && fileMenu->window() && fileMenu->window()->windowHandle())
+        QVERIFY(fileMenu->window()->windowHandle()->transientParent());
+    QTest::keyRelease(fileMenu, Qt::Key_F, Qt::AltModifier);
+
+    QTest::keyPress(fileMenu, Qt::Key_E, Qt::AltModifier);
+    QTRY_VERIFY(QTest::qWaitForWindowExposed(editMenu));
+    if (editMenu->isWindow() && editMenu->window() && editMenu->window()->windowHandle())
+        QVERIFY(editMenu->window()->windowHandle()->transientParent());
+    QTest::keyRelease(editMenu, Qt::Key_E, Qt::AltModifier);
+#endif // QT_CONFIG(shortcut) && !Q_OS_DARWIN
+
+}
+
 class MyMenu : public QMenu
 {
     Q_OBJECT