Fix issue with bindings to aliases that cannot yet be resolved

When an alias points to a child object which has not yet been
initialized, it's id won't have been registered yet, so setting up a
binding to it will result in a crash.

The fix is: when setting a binding target fails, and its target property
is an alias, queue them until all bindings have been set up, and try
again.

Task-number: QTBUG-57041
Change-Id: I4dc5a6d25c0a32fed9fd952c955e2006c76be45a
Reviewed-by: Simon Hausmann <simon.hausmann@qt.io>
(cherry picked from commit aa94c6c0469b0595f483f13ac88459f0035deef9)

1 files changed, 8 insertions, 5 deletions

diff --git a/src/qml/qml/qqmlbinding.cpp b/src/qml/qml/qqmlbinding.cpp
index 325f752cd5..6eecb305b5 100644
--- a/src/qml/qml/qqmlbinding.cpp
+++ b/src/qml/qml/qqmlbinding.cpp
@@ -465,13 +465,13 @@ void QQmlBinding::setTarget(const QQmlProperty &prop)
     setTarget(prop.object(), pd->core, &pd->valueTypeData);
 }
 
-void QQmlBinding::setTarget(QObject *object, const QQmlPropertyData &core, const QQmlPropertyData *valueType)
+bool QQmlBinding::setTarget(QObject *object, const QQmlPropertyData &core, const QQmlPropertyData *valueType)
 {
     m_target = object;
 
     if (!object) {
         m_targetIndex = QQmlPropertyIndex();
-        return;
+        return false;
     }
 
     int coreIndex = core.coreIndex();
@@ -481,9 +481,10 @@ void QQmlBinding::setTarget(QObject *object, const QQmlPropertyData &core, const
 
         int aValueTypeIndex;
         if (!vme->aliasTarget(coreIndex, &object, &coreIndex, &aValueTypeIndex)) {
-            m_target = 0;
+            // can't resolve id (yet)
+            m_target = nullptr;
             m_targetIndex = QQmlPropertyIndex();
-            return;
+            return false;
         }
         if (valueTypeIndex == -1)
             valueTypeIndex = aValueTypeIndex;
@@ -492,7 +493,7 @@ void QQmlBinding::setTarget(QObject *object, const QQmlPropertyData &core, const
         if (!data || !data->propertyCache) {
             m_target = 0;
             m_targetIndex = QQmlPropertyIndex();
-            return;
+            return false;
         }
         QQmlPropertyData *propertyData = data->propertyCache->property(coreIndex);
         Q_ASSERT(propertyData);
@@ -508,6 +509,8 @@ void QQmlBinding::setTarget(QObject *object, const QQmlPropertyData &core, const
         data->propertyCache = QQmlEnginePrivate::get(context()->engine)->cache(m_target->metaObject());
         data->propertyCache->addref();
     }
+
+    return true;
 }
 
 void QQmlBinding::getPropertyData(QQmlPropertyData **propertyData, QQmlPropertyData *valueTypeData) const