When QWidget is being destroyed, its winId is cleared, and
a QEvent::WinIdChange is sent. If a listener of this event
reacted by calling winId() again, we might crash.
A crash can be observed when this child widget is destroyed in dtor of its parent.
E.g. here is a hierarchy of widgets:
1:QWidget
2:QObject
3:QWidget
4:QWidget
If a listener subscribed for WinIdChange events from (4),
and there is a connection to destroy (4) when (2) is destroyed.
This will lead to infinite loop:
1. QWidget::~QWidget
2. QWidget::destroy
3. QWidgetPrivate::setWinId(0)
4. QCoreApplication::sendEvent(q, QEvent::WinIdChange);
5. eventFilter
6. QWidget::winId
7. QWidgetPrivate::createWinId (this=0x555555957600) at kernel/qwidget.cpp:2380
8. QWidgetPrivate::createWinId (this=0x55555596b040) at kernel/qwidget.cpp:2387
9. QWidget::create (this=0x5555558f2010, window=0, initializeWindow=true, destroyOldWindow=true) at kernel/qwidget.cpp:1163
10. QWidgetPrivate::createWinId (this=0x55555596b040) at kernel/qwidget.cpp:2387
11. QWidget::create (this=0x5555558f2010, window=0, initializeWindow=true, destroyOldWindow=true) at kernel/qwidget.cpp:1163
12. QWidgetPrivate::createWinId (this=0x55555596b040) at kernel/qwidget.cpp:2387
Fixes: QTBUG-81849
Change-Id: Ib4c33ac97d9a79c701431ae107bddfb22720ba0d
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Tor Arne Vestbø <tor.arne.vestbo@qt.io>
9ecc595d71