Cleanup: Add & use enum value for ID Outliner element type

Code to check if the Outliner tree-element type was the general ID one
would always check against "0" (explicity or even implicitly). For
somebody unfamiliar with the code this is very confusing. Instead the
value should be given a name, e.g. through an enum.

Adds `TSE_SOME_ID` as the "default" ID tree-element type. Other types
may still represent IDs, as I explained in a comment at the definition.

There may also still be cases where the type is checked against "0". I
noted in the comment that such cases should be cleaned up if found.

1 files changed, 1 insertions, 1 deletions

diff --git a/source/blender/editors/space_outliner/outliner_context.c b/source/blender/editors/space_outliner/outliner_context.c
index e2b3b79e027..4293d8da73e 100644
--- a/source/blender/editors/space_outliner/outliner_context.c
+++ b/source/blender/editors/space_outliner/outliner_context.c
@@ -34,7 +34,7 @@ static void outliner_context_selected_ids_recursive(const ListBase *subtree,
 {
   LISTBASE_FOREACH (const TreeElement *, te, subtree) {
     const TreeStoreElem *tse = TREESTORE(te);
-    if ((tse->flag & TSE_SELECTED) && (ELEM(tse->type, 0, TSE_LAYER_COLLECTION))) {
+    if ((tse->flag & TSE_SELECTED) && (ELEM(tse->type, TSE_SOME_ID, TSE_LAYER_COLLECTION))) {
       CTX_data_id_list_add(result, tse->id);
     }
     outliner_context_selected_ids_recursive(&te->subtree, result);