QObject/QWidget::setParent: add assertions to prevent loops

It is perfectly possible to accidentally create a parent/child
loop. This can happens by direct means (a->setParent(b);
b->setParent(a);), or some more subtle means, e.g.

class MyClass : public QObject {
   MyClass() : QObject(this) {}
};

Since this is UB, add a few robustness checks to make sure the
code above crashes right away (at least in debug builds).

Change-Id: I6583c8514b4c1f8a90677b04c77b8e8f0c15dba3
Reviewed-by: Liang Qi <liang.qi@qt.io>
Reviewed-by: Sérgio Martins <sergio.martins@kdab.com>
 
 
 
 
 
 
 

1 files changed, 4 insertions, 0 deletions

diff --git a/src/corelib/kernel/qobject.h b/src/corelib/kernel/qobject.h
index ad5e1163bf..7f72b69c1a 100644
--- a/src/corelib/kernel/qobject.h
+++ b/src/corelib/kernel/qobject.h
@@ -113,6 +113,10 @@ public:
     int postedEvents;
     QDynamicMetaObjectData *metaObject;
     QMetaObject *dynamicMetaObject() const;
+
+#ifdef QT_DEBUG
+    enum { CheckForParentChildLoopsWarnDepth = 4096 };
+#endif
 };