QtQml: Do not evaluate bindings in invalid contexts

If the context is gone, we are technically still able to evaluate
QProperty bindings, but we really shouldn't.

Pick-to: 6.10 6.9 6.8 6.5
Fixes: QTBUG-137270
Change-Id: I323c26d59788e4b318ec4733e1593e761beb4b6f
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Olivier De Cannière <olivier.decanniere@qt.io>

src/qml/qml/qqmlpropertybinding.cpp

@@ -133,6 +133,9 @@ QUntypedPropertyBinding QQmlPropertyBinding::createFromBoundFunction(const QQmlP
 
 void QQmlPropertyBindingJS::expressionChanged()
 {
+    if (!hasValidContext())
+        return;
+
     auto binding = asBinding();
     if (!binding->propertyDataPtr)
         return;

tests/auto/qml/qqmlbinding/data/bindingInDeadContext.qml

@@ -0,0 +1,18 @@
+import QtQml
+
+QtObject {
+    id: outer
+    objectName: "outer"
+
+    property Component c: QtObject {
+        id: inner1
+        objectName: inner2.objectName + "a"
+    }
+
+    property QtObject inner1: c.createObject()
+
+    property QtObject inner2: QtObject {
+        id: inner2
+        objectName: "a"
+    }
+}

tests/auto/qml/qqmlbinding/tst_qqmlbinding.cpp

@@ -41,6 +41,7 @@ private slots:
     void disabledOnReadonlyProperty();
     void delayed();
     void bindingOverwriting();
+    void bindingInDeadContext();
     void bindToQmlComponent();
     void bindingDoesNoWeirdConversion();
     void bindNaNToInt();
@@ -500,6 +501,40 @@ void tst_qqmlbinding::bindingOverwriting()
     QLoggingCategory::setFilterRules(QString());
 }
 
+void tst_qqmlbinding::bindingInDeadContext()
+{
+    // We manually control the deletion order of the objects here.
+    // This is what some of our views also do. One way to prevent
+    // the engine from deleting objects is to parent them to the
+    // application.
+
+    QScopedPointer<QObject> o;
+    QScopedPointer<QObject> inner1;
+    {
+        QScopedPointer<QObject> inner2;
+
+        QQmlEngine engine;
+        QQmlComponent c(&engine, testFileUrl("bindingInDeadContext.qml"));
+
+        QVERIFY2(c.isReady(), qPrintable(c.errorString()));
+        o.reset(c.create());
+        QVERIFY(!o.isNull());
+        o->setParent(QCoreApplication::instance());
+
+        inner1.reset(o->property("inner1").value<QObject *>());
+        QVERIFY(inner1);
+        inner1->setParent(QCoreApplication::instance());
+
+        inner2.reset(o->property("inner2").value<QObject *>());
+        QVERIFY(inner2);
+        inner2->setParent(QCoreApplication::instance());
+    }
+
+    // The objectName binding did not get re-evaluated when inner2 died
+    // because the engine was gone already.
+    QCOMPARE(inner1->objectName(), "aa");
+}
+
 void tst_qqmlbinding::bindToQmlComponent()
 {
     QQmlEngine engine;