Fix collection syncing when creating new collections from the outliner

We were not passing a scene collection parent to the BKE_collection_add
function, which in turn made syncing not work.

Right now we:
* Explicitly pass the master collection in this case
* Fallback to the master collection in other cases

With unittest.

3 files changed, 7 insertions, 1 deletions

diff --git a/source/blender/blenkernel/intern/collection.c b/source/blender/blenkernel/intern/collection.c
index 729be02bfc7..69168c4dd3d 100644
--- a/source/blender/blenkernel/intern/collection.c
+++ b/source/blender/blenkernel/intern/collection.c
@@ -111,6 +111,10 @@ static SceneCollection *collection_add(ID *owner_id, SceneCollection *sc_parent,
  */
 SceneCollection *BKE_collection_add(ID *owner_id, SceneCollection *sc_parent, const int type, const char *name_custom)
 {
+	if (sc_parent == NULL) {
+		sc_parent = BKE_collection_master(owner_id);
+	}
+
 	SceneCollection *scene_collection = collection_add(owner_id, sc_parent, type, name_custom);
 	BKE_layer_sync_new_scene_collection(owner_id, sc_parent, scene_collection);
 	return scene_collection;
diff --git a/source/blender/blenkernel/intern/layer.c b/source/blender/blenkernel/intern/layer.c
index 9807c6e4f10..cb7b72bdabd 100644
--- a/source/blender/blenkernel/intern/layer.c
+++ b/source/blender/blenkernel/intern/layer.c
@@ -375,6 +375,7 @@ static void layer_collection_sync_flags(
 
 static void layer_collections_sync_flags(ListBase *layer_collections_dst, const ListBase *layer_collections_src)
 {
+	BLI_assert(BLI_listbase_count(layer_collections_dst) == BLI_listbase_count(layer_collections_src));
 	LayerCollection *layer_collection_dst = (LayerCollection *)layer_collections_dst->first;
 	const LayerCollection *layer_collection_src = (const LayerCollection *)layer_collections_src->first;
 	while (layer_collection_dst != NULL) {
diff --git a/source/blender/editors/space_outliner/outliner_collections.c b/source/blender/editors/space_outliner/outliner_collections.c
index be4c8f62085..3d5f12a94fd 100644
--- a/source/blender/editors/space_outliner/outliner_collections.c
+++ b/source/blender/editors/space_outliner/outliner_collections.c
@@ -342,7 +342,8 @@ static int collection_new_exec(bContext *C, wmOperator *UNUSED(op))
 	Main *bmain = CTX_data_main(C);
 	Scene *scene = CTX_data_scene(C);
 	ViewLayer *view_layer = CTX_data_view_layer(C);
-	SceneCollection *scene_collection = BKE_collection_add(&scene->id, NULL, COLLECTION_TYPE_NONE, NULL);
+	SceneCollection *scene_collection_parent = BKE_collection_master(&scene->id);
+	SceneCollection *scene_collection = BKE_collection_add(&scene->id, scene_collection_parent, COLLECTION_TYPE_NONE, NULL);
 	BKE_collection_link(view_layer, scene_collection);
 
 	DEG_relations_tag_update(bmain);