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>

2 files changed, 26 insertions, 0 deletions

diff --git a/src/widgets/widgets/qmenu.cpp b/src/widgets/widgets/qmenu.cpp
index 5ecac2c7c6..c6d1dd0e7e 100644
--- a/src/widgets/widgets/qmenu.cpp
+++ b/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:
diff --git a/src/widgets/widgets/qmenu_p.h b/src/widgets/widgets/qmenu_p.h
index ffe956d007..bad9c294f8 100644
--- a/src/widgets/widgets/qmenu_p.h
+++ b/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); }