Add QWidgetPrivate::closestParentWidgetWithWindowHandle helper method

In contrast to nativeParentWidget(), we return the closest widget with a
QWindow, even if this window has not been created yet.

Pick-to: 6.6 6.5
Change-Id: Icac46297a6052a7a5698d752d4aa871bd5c2bdd8
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
(cherry picked from commit b571634172428263fa83ac733cf89e664bded014)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/widgets/kernel/qwidget.cpp

@@ -1029,6 +1029,23 @@ void QWidgetPrivate::createRecursively()
     }
 }
 
+/*!
+    \internal
+    Returns the closest parent widget that has a QWindow window handle
+
+    \note This behavior is different from nativeParentWidget(), which
+    returns the closest parent that has a QWindow window handle with
+    a created QPlatformWindow, and hence native window (winId).
+*/
+QWidget *QWidgetPrivate::closestParentWidgetWithWindowHandle() const
+{
+    Q_Q(const QWidget);
+    QWidget *parent = q->parentWidget();
+    while (parent && !parent->windowHandle())
+        parent = parent->parentWidget();
+    return parent;
+}
+
 QWindow *QWidgetPrivate::windowHandle(WindowHandleMode mode) const
 {
     if (mode == WindowHandleMode::Direct || mode == WindowHandleMode::Closest) {
@@ -1038,6 +1055,7 @@ QWindow *QWidgetPrivate::windowHandle(WindowHandleMode mode) const
         }
     }
     if (mode == WindowHandleMode::Closest) {
+        // FIXME: Use closestParentWidgetWithWindowHandle instead
         if (auto nativeParent = q_func()->nativeParentWidget()) {
             if (auto window = nativeParent->windowHandle())
                 return window;

src/widgets/kernel/qwidget_p.h

@@ -635,6 +635,8 @@ public:
 
     std::string flagsForDumping() const override;
 
+    QWidget *closestParentWidgetWithWindowHandle() const;
+
     // Variables.
     // Regular pointers (keep them together to avoid gaps on 64 bit architectures).
     std::unique_ptr<QWExtra> extra;