LibOverride: Add 'hierarchy root ID' info.

This change will make handling of liboverrides hierarchies (especially
resyncing) much easier and efficient. It should also make it more
resilient to 'degenerate' cases, and allow proper support of things like
parenting an override to another override of the same linked data (e.g.
a override character parented to another override of the same
character).

NOTE: this commit only implements minimal changes to add that data and
generate it for existing files on load. Actual refactor of resync code
to take advantage of this new info will happen separately.

1 files changed, 7 insertions, 0 deletions

diff --git a/source/blender/editors/interface/interface_templates.c b/source/blender/editors/interface/interface_templates.c
index 1f81dd21b83..03d0cba5ec8 100644
--- a/source/blender/editors/interface/interface_templates.c
+++ b/source/blender/editors/interface/interface_templates.c
@@ -667,6 +667,13 @@ static void template_id_cb(bContext *C, void *arg_litem, void *arg_event)
 
               /* Assign new pointer, takes care of updates/notifiers */
               RNA_id_pointer_create(override_id, &idptr);
+              /* Insert into override hierarchy if possible. */
+              ID *owner_id = template_ui->ptr.owner_id;
+              if (owner_id != NULL && ID_IS_OVERRIDE_LIBRARY_REAL(owner_id)) {
+                override_id->override_library->hierarchy_root =
+                    owner_id->override_library->hierarchy_root;
+                owner_id->override_library->flag &= ~IDOVERRIDE_LIBRARY_FLAG_NO_HIERARCHY;
+              }
             }
             undo_push_label = "Make Library Override";
           }