QQmlVMEMetaObjectEndpoint: ensure property cache before accessing it

Otherwise the property cache might be null and lead to segmentation
faults, e.g. when declaring aliases in qml.

In dev, ensurePropertyCache() does not require the engine argument anymore
such that this cherry-pick diverges here.
To get the engine argument, use qjsEngine() on the object. If this fail,
return.

Fixes: QTBUG-106256
Change-Id: I568c973e1ba00531fbe22a41e2c6c3c09dfc2f02
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>
(cherry picked from commit e0a00a691963e2c684f4dd857d042a3ffbebe959)
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/src/qml/qml/qqmlvmemetaobject.cpp b/src/qml/qml/qqmlvmemetaobject.cpp
index ee1b2058d1..9b5823740d 100644
--- a/src/qml/qml/qqmlvmemetaobject.cpp
+++ b/src/qml/qml/qqmlvmemetaobject.cpp
@@ -240,13 +240,14 @@ void QQmlVMEMetaObjectEndpoint::tryConnect()
             if (!target)
                 return;
 
-            QQmlData *targetDData = QQmlData::get(target, /*create*/false);
-            if (!targetDData)
-                return;
             QQmlPropertyIndex encodedIndex = QQmlPropertyIndex::fromEncoded(aliasData->encodedMetaPropertyIndex);
             int coreIndex = encodedIndex.coreIndex();
             int valueTypeIndex = encodedIndex.valueTypeIndex();
-            const QQmlPropertyData *pd = targetDData->propertyCache->property(coreIndex);
+            QJSEngine *engine = qjsEngine(target);
+            if (!engine)
+                return; // dont crash
+            const QQmlPropertyData *pd =
+                    QQmlData::ensurePropertyCache(engine, target)->property(coreIndex);
             if (pd && valueTypeIndex != -1 && !QQmlMetaType::valueType(pd->propType())) {
                 // deep alias
                 QQmlEnginePrivate *enginePriv = QQmlEnginePrivate::get(metaObject->compilationUnit->engine->qmlEngine());