Fix T77460: Easy to create cyclic dependencies in collections and crash Blender.

Cyclic check was not checking for collections instanciated by objects...

1 files changed, 23 insertions, 1 deletions

diff --git a/source/blender/blenkernel/intern/collection.c b/source/blender/blenkernel/intern/collection.c
index eda2c6b01da..8267e38fcad 100644
--- a/source/blender/blenkernel/intern/collection.c
+++ b/source/blender/blenkernel/intern/collection.c
@@ -969,6 +969,26 @@ void BKE_collections_after_lib_link(Main *bmain)
 
 /********************** Collection Children *******************/
 
+static bool collection_find_instance_recursive(Collection *collection,
+                                               Collection *instance_collection)
+{
+  LISTBASE_FOREACH (CollectionObject *, collection_object, &collection->gobject) {
+    if (collection_object->ob != NULL &&
+        /* Object from a given collection should never instanciate that collection either. */
+        ELEM(collection_object->ob->instance_collection, instance_collection, collection)) {
+      return true;
+    }
+  }
+
+  LISTBASE_FOREACH (CollectionChild *, collection_child, &collection->children) {
+    if (collection_find_instance_recursive(collection_child->collection, instance_collection)) {
+      return true;
+    }
+  }
+
+  return false;
+}
+
 bool BKE_collection_find_cycle(Collection *new_ancestor, Collection *collection)
 {
   if (collection == new_ancestor) {
@@ -981,7 +1001,9 @@ bool BKE_collection_find_cycle(Collection *new_ancestor, Collection *collection)
     }
   }
 
-  return false;
+  /* Find possible objects in collection or its children, that would instanciate the given ancestor
+   * collection (that would also make a fully invalid cycle of dependencies) .*/
+  return collection_find_instance_recursive(collection, new_ancestor);
 }
 
 static CollectionChild *collection_find_child(Collection *parent, Collection *collection)