Check for invalid context in QQmlContextPrivate::dropDestroyedQObject

If the context is invalid we won't be able to look up the object by name
anymore. In that case there is nothing to do.

Fixes: QTBUG-78326
Change-Id: I011ccb6b02a84725c1d5eae24b494516ae2d5fee
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>

2 files changed, 21 insertions, 7 deletions

diff --git a/src/qml/qml/qqmlcontext.cpp b/src/qml/qml/qqmlcontext.cpp
index af8deb085c..f75a076bcb 100644
--- a/src/qml/qml/qqmlcontext.cpp
+++ b/src/qml/qml/qqmlcontext.cpp
@@ -532,6 +532,9 @@ QObject *QQmlContextPrivate::context_at(QQmlListProperty<QObject> *prop, int ind
 
 void QQmlContextPrivate::dropDestroyedQObject(const QString &name, QObject *destroyed)
 {
+    if (!data->isValid())
+        return;
+
     const int idx = data->propertyNames().value(name);
     Q_ASSERT(idx >= 0);
     if (qvariant_cast<QObject *>(propertyValues[idx]) != destroyed)
diff --git a/tests/auto/qml/qqmlcontext/tst_qqmlcontext.cpp b/tests/auto/qml/qqmlcontext/tst_qqmlcontext.cpp
index d9cb6673df..6754f22049 100644
--- a/tests/auto/qml/qqmlcontext/tst_qqmlcontext.cpp
+++ b/tests/auto/qml/qqmlcontext/tst_qqmlcontext.cpp
@@ -895,16 +895,27 @@ void tst_qqmlcontext::contextObjectHierarchy()
 
 void tst_qqmlcontext::destroyContextProperty()
 {
-    QQmlEngine engine;
-    QQmlContext context(&engine);
-
+    QScopedPointer<QQmlContext> context;
+    QScopedPointer<QObject> objectThatOutlivesEngine(new QObject);
     {
-        QObject object;
-        context.setContextProperty(QLatin1String("a"), &object);
-        QCOMPARE(qvariant_cast<QObject *>(context.contextProperty(QLatin1String("a"))), &object);
+        QQmlEngine engine;
+        context.reset(new QQmlContext(&engine));
+
+        {
+            QObject object;
+            context->setContextProperty(QLatin1String("a"), &object);
+            QCOMPARE(qvariant_cast<QObject *>(context->contextProperty(QLatin1String("a"))), &object);
+        }
+
+        QCOMPARE(qvariant_cast<QObject *>(context->contextProperty(QLatin1String("a"))), nullptr);
+        context->setContextProperty(QLatin1String("b"), objectThatOutlivesEngine.data());
     }
 
-    QCOMPARE(qvariant_cast<QObject *>(context.contextProperty(QLatin1String("a"))), nullptr);
+    // dropDestroyedObject() should not crash, even if the engine is gone.
+    objectThatOutlivesEngine.reset();
+
+    // We're not allowed to call context->contextProperty("b") anymore.
+    // TODO: Or are we?
 }
 
 QTEST_MAIN(tst_qqmlcontext)