DelegateModel: Zero foreign context objects when they are deleted

If we keep plain pointers to objects we don't own, we need to zero them
when something else deletes them.

Fixes: QTBUG-73733
Change-Id: Ib4f3e144f10f70ab6cf44af4ffa62725470d3972
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>

2 files changed, 17 insertions, 1 deletions

diff --git a/src/qml/types/qqmldelegatemodel.cpp b/src/qml/types/qqmldelegatemodel.cpp
index 57bbf7465d..48cc77bc3d 100644
--- a/src/qml/types/qqmldelegatemodel.cpp
+++ b/src/qml/types/qqmldelegatemodel.cpp
@@ -1060,7 +1060,11 @@ QObject *QQmlDelegateModelPrivate::object(Compositor::Group group, int index, QQ
                     = qobject_cast<QQmlAdaptorModelProxyInterface *>(cacheItem)) {
                 ctxt = new QQmlContextData;
                 ctxt->setParent(cacheItem->contextData, /*stronglyReferencedByParent*/true);
-                ctxt->contextObject = proxy->proxiedObject();
+                QObject *proxied = proxy->proxiedObject();
+                ctxt->contextObject = proxied;
+                // We don't own the proxied object. We need to clear it if it goes away.
+                QObject::connect(proxied, &QObject::destroyed,
+                                 cacheItem, &QQmlDelegateModelItem::childContextObjectDestroyed);
             }
         }
 
@@ -2009,6 +2013,17 @@ QV4::ReturnedValue QQmlDelegateModelItem::get_index(QQmlDelegateModelItem *thisI
     return QV4::Encode((int)thisItem->groupIndex(Compositor::Group(flag)));
 }
 
+void QQmlDelegateModelItem::childContextObjectDestroyed(QObject *childContextObject)
+{
+    if (!contextData)
+        return;
+
+    for (QQmlContextData *ctxt = contextData->childContexts; ctxt; ctxt = ctxt->nextChild) {
+        if (ctxt->contextObject == childContextObject)
+            ctxt->contextObject = nullptr;
+    }
+}
+
 
 //---------------------------------------------------------------------------
 
diff --git a/src/qml/types/qqmldelegatemodel_p_p.h b/src/qml/types/qqmldelegatemodel_p_p.h
index 2d6fdf228e..5e480f4df6 100644
--- a/src/qml/types/qqmldelegatemodel_p_p.h
+++ b/src/qml/types/qqmldelegatemodel_p_p.h
@@ -106,6 +106,7 @@ public:
     void referenceObject() { ++objectRef; }
     bool releaseObject() { return --objectRef == 0 && !(groups & Compositor::PersistedFlag); }
     bool isObjectReferenced() const { return objectRef != 0 || (groups & Compositor::PersistedFlag); }
+    void childContextObjectDestroyed(QObject *childContextObject);
 
     bool isReferenced() const {
         return scriptRef