Merge branch '5.12' into 5.13

Change-Id: If17511da64dd666a536408aa3cb3178ef6db0403

3 files changed, 32 insertions, 6 deletions

diff --git a/src/core/nodes/qentity.cpp b/src/core/nodes/qentity.cpp
index 3c8805a67..69d774dd1 100644
--- a/src/core/nodes/qentity.cpp
+++ b/src/core/nodes/qentity.cpp
@@ -159,6 +159,8 @@ void QEntity::addComponent(QComponent *comp)
     if (!comp->parent())
         comp->setParent(this);
 
+    QNodePrivate::get(comp)->_q_ensureBackendNodeCreated();
+
     d->m_components.append(comp);
 
     // Ensures proper bookkeeping
diff --git a/src/core/nodes/qnode.cpp b/src/core/nodes/qnode.cpp
index 83ac49471..c2373b805 100644
--- a/src/core/nodes/qnode.cpp
+++ b/src/core/nodes/qnode.cpp
@@ -394,15 +394,15 @@ void QNodePrivate::propertyChanged(int propertyIndex)
         if (data.canConvert<QNode*>()) {
             QNode *node = data.value<QNode*>();
 
-            // Ensure the node has issued a node creation change. We can end
-            // up here if a newly created node with a parent is immediately set
+            // Ensure the node and all ancestors have issued their node creation changes.
+            // We can end up here if a newly created node with a parent is immediately set
             // as a property on another node. In this case the deferred call to
             // _q_postConstructorInit() will not have happened yet as the event
-            // loop will still be blocked. So force it here and we catch this
-            // eventuality in the _q_postConstructorInit() function so that we
-            // do not repeat the creation and new child scene change events.
+            // loop will still be blocked. We need to do this for all ancestors,
+            // since the subtree of this node otherwise can end up on the backend
+            // with a reference to a non-existent parent.
             if (node)
-                QNodePrivate::get(node)->_q_postConstructorInit();
+                QNodePrivate::get(node)->_q_ensureBackendNodeCreated();
 
             const QNodeId id = node ? node->id() : QNodeId();
             return QVariant::fromValue(id);
@@ -506,6 +506,29 @@ void QNodePrivate::setArbiter(QLockableObserverInterface *arbiter)
 }
 
 /*!
+ * \internal
+ * Makes sure this node has a backend by traversing the tree up to the most distant ancestor
+ * without a backend node and initializing that node. This is done to make sure the parent nodes
+ * are always created before the child nodes, since child nodes reference parent nodes at creation
+ * time.
+ */
+void QNodePrivate::_q_ensureBackendNodeCreated()
+{
+    if (m_hasBackendNode)
+        return;
+
+    Q_Q(QNode);
+
+    QNode *nextNode = q;
+    QNode *topNodeWithoutBackend = nullptr;
+    while (nextNode != nullptr && !QNodePrivate::get(nextNode)->m_hasBackendNode) {
+        topNodeWithoutBackend = nextNode;
+        nextNode = nextNode->parentNode();
+    }
+    QNodePrivate::get(topNodeWithoutBackend)->_q_postConstructorInit();
+}
+
+/*!
     \class Qt3DCore::QNode
     \inherits QObject
 
diff --git a/src/core/nodes/qnode_p.h b/src/core/nodes/qnode_p.h
index 73893cc1e..6ffb19ce8 100644
--- a/src/core/nodes/qnode_p.h
+++ b/src/core/nodes/qnode_p.h
@@ -152,6 +152,7 @@ public:
     static const QMetaObject *findStaticMetaObject(const QMetaObject *metaObject);
 
     void _q_postConstructorInit();
+    void _q_ensureBackendNodeCreated();
 
 private:
     void notifyCreationChange();