QProperty: Downgrade assert in noSelfDependencies to warning

We call evaluateRecursive_inline in setBinding, which in turns runs the
noSelfDependecies check. However, creating a binding resuting in a
binding loop must not crash, but instead result in the binding entering
an error state. To prevent a crash caused by the assert in debug builds
of Qt, we replace the assert with a warning for now.
A better approach in the future would be to ensure that we only run the
check in cases where we are sure that a self-dependency is really a
fatal error.

Pick-to: 6.2
Change-Id: I58158864ed81fa907132a4e7d6667c9b529e7e64
Reviewed-by: Maximilian Goldstein <max.goldstein@qt.io>

src/corelib/kernel/qproperty.cpp

@@ -744,7 +744,10 @@ void QPropertyObserverPointer::noSelfDependencies(QPropertyBindingPrivate *bindi
     // See also comment in notify()
     while (observer) {
         if (QPropertyObserver::ObserverTag(observer->next.tag()) == QPropertyObserver::ObserverNotifiesBinding)
-            Q_ASSERT(observer->binding != binding);
+            if (observer->binding == binding) {
+                qCritical("Property depends on itself!");
+                break;
+            }
 
         observer = observer->next.data();
     }

tests/auto/corelib/kernel/qproperty/tst_qproperty.cpp

@@ -113,6 +113,8 @@ private slots:
     void notify();
 
     void bindableInterfaceOfCompatPropertyUsesSetter();
+
+    void selfBindingShouldNotCrash();
 };
 
 void tst_QProperty::functorBinding()
@@ -1847,6 +1849,13 @@ void tst_QProperty::bindableInterfaceOfCompatPropertyUsesSetter()
     QCOMPARE(obj.setCompatCalled, 1);
 }
 
+void tst_QProperty::selfBindingShouldNotCrash()
+{
+    QProperty<int> i;
+    i.setBinding([&](){ return i+1; });
+    QVERIFY(i.binding().error().hasError());
+}
+
 QTEST_MAIN(tst_QProperty);
 
 #undef QT_SOURCE_LOCATION_NAMESPACE