Prevent recursive calls to QWindow::close

QWidget will call close() in its destructor, which we might end up
in if a user deletes the widget in the closeEvent.

Pick-to: 6.2
Change-Id: I39684aec0ca130033dad60f2bbf823364a5edcec
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/gui/kernel/qwindow.cpp

@@ -2257,6 +2257,8 @@ void QWindow::showNormal()
 bool QWindow::close()
 {
     Q_D(QWindow);
+    if (d->inClose)
+        return true;
 
     // Do not close non top level windows
     if (!isTopLevel())

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

@@ -1602,6 +1602,23 @@ void tst_QWindow::sizes()
     QCOMPARE(maximumHeightSpy.count(), 1);
 }
 
+class CloseOnCloseEventWindow : public QWindow
+{
+public:
+    inline static int closeEvents;
+    CloseOnCloseEventWindow() { closeEvents = 0; }
+
+protected:
+    void closeEvent(QCloseEvent *e) override
+    {
+        if (++closeEvents > 1)
+            return;
+
+        close();
+        e->accept();
+    }
+};
+
 void tst_QWindow::close()
 {
     {
@@ -1683,6 +1700,16 @@ void tst_QWindow::close()
             QVERIFY(c.handle());
         }
     }
+
+    {
+        // A QWidget will call close() from the destructor, and
+        // we allow widgets deleting itself in the closeEvent,
+        // so we need to guard against close being called recursively.
+        CloseOnCloseEventWindow w;
+        w.create();
+        w.close();
+        QCOMPARE(CloseOnCloseEventWindow::closeEvents, 1);
+    }
 }
 
 void tst_QWindow::activateAndClose()