Avoid misleading bindingStatus

Set it to nullptr on clear, and deal with possibly null bindingStatus.

Task-number: QTBUG-101177
Task-number: QTBUG-102403
Pick-to: 6.4
Change-Id: I66cb4d505a4f7b377dc90b45ac13834fca19d399
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

src/corelib/kernel/qbindingstorage.h

@@ -55,7 +55,7 @@ public:
 
     void registerDependency(const QUntypedPropertyData *data) const
     {
-        if (!bindingStatus->currentlyEvaluatingBinding)
+        if (!bindingStatus || !bindingStatus->currentlyEvaluatingBinding)
             return;
         registerDependency_helper(data);
     }

src/corelib/kernel/qobject.cpp

@@ -1873,9 +1873,9 @@ void QObjectPrivate::moveToThread_helper()
     Q_Q(QObject);
     QEvent e(QEvent::ThreadChange);
     QCoreApplication::sendEvent(q, &e);
+    bindingStorage.clear();
     for (int i = 0; i < children.size(); ++i) {
         QObject *child = children.at(i);
-        child->d_func()->bindingStorage.clear();
         child->d_func()->moveToThread_helper();
     }
 }

src/corelib/kernel/qproperty.cpp

@@ -2193,6 +2193,7 @@ void QBindingStorage::clear()
 {
     QBindingStoragePrivate(d).destroy();
     d = nullptr;
+    bindingStatus = nullptr;
 }
 
 void QBindingStorage::registerDependency_helper(const QUntypedPropertyData *data) const

src/corelib/kernel/qproperty_p.h

@@ -442,7 +442,7 @@ class QObjectCompatProperty : public QPropertyData<T>
     }
     bool inBindingWrapper(const QBindingStorage *storage) const
     {
-        return storage->bindingStatus->currentCompatProperty
+        return storage->bindingStatus && storage->bindingStatus->currentCompatProperty
             && QtPrivate::isPropertyInBindingWrapper(this);
     }
 
@@ -467,7 +467,7 @@ public:
     {
         const QBindingStorage *storage = qGetBindingStorage(owner());
         // make sure we don't register this binding as a dependency to itself
-        if (storage->bindingStatus->currentlyEvaluatingBinding && !inBindingWrapper(storage))
+        if (storage->bindingStatus && storage->bindingStatus->currentlyEvaluatingBinding && !inBindingWrapper(storage))
             storage->registerDependency_helper(this);
         return this->val;
     }

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

@@ -79,6 +79,7 @@ private slots:
 
     void noFakeDependencies();
     void threadSafety();
+    void threadSafety2();
 
     void bindablePropertyWithInitialization();
     void noDoubleNotification();
@@ -1694,7 +1695,7 @@ void tst_QProperty::threadSafety()
     auto child1 = new ThreadSafetyTester(obj1);
     obj1->moveToThread(&workerThread);
     const auto mainThreadBindingStatus = QtPrivate::getBindingStatus({});
-    QCOMPARE(qGetBindingStorage(child1)->status({}), mainThreadBindingStatus);
+    QCOMPARE(qGetBindingStorage(child1)->status({}), nullptr);
     workerThread.start();
 
     bool correctStatus = false;
@@ -1743,6 +1744,41 @@ void tst_QProperty::threadSafety()
     QCOMPARE(obj3->objectName(), "moved again");
 }
 
+class QPropertyUsingThread : public QThread
+{
+public:
+    QPropertyUsingThread(QObject **dest, QThread *destThread) : dest(dest), destThread(destThread) {}
+    void run() override
+    {
+        scopedObj1.reset(new ThreadSafetyTester());
+        scopedObj1->setObjectName("test");
+        QObject *child = new ThreadSafetyTester(scopedObj1.get());
+        child->setObjectName("child");
+        exec();
+        scopedObj1->moveToThread(destThread);
+        *dest = scopedObj1.release();
+    }
+    std::unique_ptr<ThreadSafetyTester> scopedObj1;
+    QObject **dest;
+    QThread *destThread;
+};
+
+void tst_QProperty::threadSafety2()
+{
+    std::unique_ptr<QObject> movedObj;
+    {
+        QObject *tmp = nullptr;
+        QPropertyUsingThread workerThread(&tmp, QThread::currentThread());
+        workerThread.start();
+        workerThread.quit();
+        workerThread.wait();
+        movedObj.reset(tmp);
+    }
+
+    QCOMPARE(movedObj->objectName(), "test");
+    QCOMPARE(movedObj->children().first()->objectName(), "child");
+}
+
 struct CustomType
 {
     CustomType() = default;