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, 27 insertions, 24 deletions

diff --git a/source/blender/editors/space_outliner/outliner_tree.c b/source/blender/editors/space_outliner/outliner_tree.c
index 0d82ba992c2..3696ef8dbce 100644
--- a/source/blender/editors/space_outliner/outliner_tree.c
+++ b/source/blender/editors/space_outliner/outliner_tree.c
@@ -307,7 +307,7 @@ static void outliner_add_line_styles(SpaceOutliner *space_outliner,
           continue;
         }
         linestyle->id.tag &= ~LIB_TAG_DOIT;
-        outliner_add_element(space_outliner, lb, linestyle, te, 0, 0);
+        outliner_add_element(space_outliner, lb, linestyle, te, TSE_SOME_ID, 0);
       }
     }
   }
@@ -332,7 +332,7 @@ static void outliner_add_scene_contents(SpaceOutliner *space_outliner,
   }
 
   /* World */
-  outliner_add_element(space_outliner, lb, sce->world, te, 0, 0);
+  outliner_add_element(space_outliner, lb, sce->world, te, TSE_SOME_ID, 0);
 
   /* Collections */
   ten = outliner_add_element(space_outliner, lb, &sce->id, te, TSE_SCENE_COLLECTION_BASE, 0);
@@ -343,7 +343,7 @@ static void outliner_add_scene_contents(SpaceOutliner *space_outliner,
   ten = outliner_add_element(space_outliner, lb, sce, te, TSE_SCENE_OBJECTS_BASE, 0);
   ten->name = IFACE_("Objects");
   FOREACH_SCENE_OBJECT_BEGIN (sce, ob) {
-    outliner_add_element(space_outliner, &ten->subtree, ob, ten, 0, 0);
+    outliner_add_element(space_outliner, &ten->subtree, ob, ten, TSE_SOME_ID, 0);
   }
   FOREACH_SCENE_OBJECT_END;
   outliner_make_object_parent_hierarchy(&ten->subtree);
@@ -368,14 +368,14 @@ static void outliner_add_object_contents(SpaceOutliner *space_outliner,
                        &te->subtree,
                        ob->poselib,
                        te,
-                       0,
+                       TSE_SOME_ID,
                        0); /* XXX FIXME.. add a special type for this. */
 
   if (ob->proxy && !ID_IS_LINKED(ob)) {
     outliner_add_element(space_outliner, &te->subtree, ob->proxy, te, TSE_PROXY, 0);
   }
 
-  outliner_add_element(space_outliner, &te->subtree, ob->data, te, 0, 0);
+  outliner_add_element(space_outliner, &te->subtree, ob->data, te, TSE_SOME_ID, 0);
 
   if (ob->pose) {
     bArmature *arm = ob->data;
@@ -458,7 +458,7 @@ static void outliner_add_object_contents(SpaceOutliner *space_outliner,
   }
 
   for (int a = 0; a < ob->totcol; a++) {
-    outliner_add_element(space_outliner, &te->subtree, ob->mat[a], te, 0, a);
+    outliner_add_element(space_outliner, &te->subtree, ob->mat[a], te, TSE_SOME_ID, a);
   }
 
   if (!BLI_listbase_is_empty(&ob->constraints)) {
@@ -624,7 +624,8 @@ static void outliner_add_object_contents(SpaceOutliner *space_outliner,
 
   /* duplicated group */
   if (ob->instance_collection && (ob->transflag & OB_DUPLICOLLECTION)) {
-    outliner_add_element(space_outliner, &te->subtree, ob->instance_collection, te, 0, 0);
+    outliner_add_element(
+        space_outliner, &te->subtree, ob->instance_collection, te, TSE_SOME_ID, 0);
   }
 }
 
@@ -686,9 +687,9 @@ static void outliner_add_id_contents(SpaceOutliner *space_outliner,
         outliner_add_element(space_outliner, &te->subtree, me, te, TSE_ANIM_DATA, 0);
       }
 
-      outliner_add_element(space_outliner, &te->subtree, me->key, te, 0, 0);
+      outliner_add_element(space_outliner, &te->subtree, me->key, te, TSE_SOME_ID, 0);
       for (int a = 0; a < me->totcol; a++) {
-        outliner_add_element(space_outliner, &te->subtree, me->mat[a], te, 0, a);
+        outliner_add_element(space_outliner, &te->subtree, me->mat[a], te, TSE_SOME_ID, a);
       }
       /* could do tfaces with image links, but the images are not grouped nicely.
        * would require going over all tfaces, sort images in use. etc... */
@@ -702,7 +703,7 @@ static void outliner_add_id_contents(SpaceOutliner *space_outliner,
       }
 
       for (int a = 0; a < cu->totcol; a++) {
-        outliner_add_element(space_outliner, &te->subtree, cu->mat[a], te, 0, a);
+        outliner_add_element(space_outliner, &te->subtree, cu->mat[a], te, TSE_SOME_ID, a);
       }
       break;
     }
@@ -714,7 +715,7 @@ static void outliner_add_id_contents(SpaceOutliner *space_outliner,
       }
 
       for (int a = 0; a < mb->totcol; a++) {
-        outliner_add_element(space_outliner, &te->subtree, mb->mat[a], te, 0, a);
+        outliner_add_element(space_outliner, &te->subtree, mb->mat[a], te, TSE_SOME_ID, a);
       }
       break;
     }
@@ -730,7 +731,7 @@ static void outliner_add_id_contents(SpaceOutliner *space_outliner,
       if (outliner_animdata_test(tex->adt)) {
         outliner_add_element(space_outliner, &te->subtree, tex, te, TSE_ANIM_DATA, 0);
       }
-      outliner_add_element(space_outliner, &te->subtree, tex->ima, te, 0, 0);
+      outliner_add_element(space_outliner, &te->subtree, tex->ima, te, TSE_SOME_ID, 0);
       break;
     }
     case ID_CA: {
@@ -1008,7 +1009,7 @@ TreeElement *outliner_add_element(SpaceOutliner *space_outliner,
   if (te->type) {
     outliner_tree_element_type_expand(te->type, space_outliner);
   }
-  else if (type == 0) {
+  else if (type == TSE_SOME_ID) {
     TreeStoreElem *tsepar = parent ? TREESTORE(parent) : NULL;
 
     /* ID data-block. */
@@ -1229,7 +1230,7 @@ BLI_INLINE void outliner_add_collection_objects(SpaceOutliner *space_outliner,
                                                 TreeElement *parent)
 {
   LISTBASE_FOREACH (CollectionObject *, cob, &collection->gobject) {
-    outliner_add_element(space_outliner, tree, cob->ob, parent, 0, 0);
+    outliner_add_element(space_outliner, tree, cob->ob, parent, TSE_SOME_ID, 0);
   }
 }
 
@@ -1240,7 +1241,8 @@ static TreeElement *outliner_add_collection_recursive(SpaceOutliner *space_outli
   outliner_add_collection_init(ten, collection);
 
   LISTBASE_FOREACH (CollectionChild *, child, &collection->children) {
-    outliner_add_element(space_outliner, &ten->subtree, &child->collection->id, ten, 0, 0);
+    outliner_add_element(
+        space_outliner, &ten->subtree, &child->collection->id, ten, TSE_SOME_ID, 0);
   }
 
   if (space_outliner->outlinevis != SO_SCENES) {
@@ -1265,7 +1267,7 @@ void outliner_make_object_parent_hierarchy(ListBase *lb)
     TreeElement *ten = te->next;
     TreeStoreElem *tselem = TREESTORE(te);
 
-    if (tselem->type == 0 && te->idcode == ID_OB) {
+    if ((tselem->type == TSE_SOME_ID) && te->idcode == ID_OB) {
       Object *ob = (Object *)tselem->id;
       if (ob->parent && ob->parent->id.newid) {
         BLI_remlink(lb, te);
@@ -1406,7 +1408,7 @@ static void outliner_sort(ListBase *lb)
 
   /* sorting rules; only object lists, ID lists, or deformgroups */
   if (ELEM(tselem->type, TSE_DEFGROUP, TSE_ID_BASE) ||
-      (tselem->type == 0 && te->idcode == ID_OB)) {
+      ((tselem->type == TSE_SOME_ID) && (te->idcode == ID_OB))) {
     int totelem = BLI_listbase_count(lb);
 
     if (totelem > 1) {
@@ -1420,7 +1422,7 @@ static void outliner_sort(ListBase *lb)
         tp->name = te->name;
         tp->idcode = te->idcode;
 
-        if (tselem->type && tselem->type != TSE_DEFGROUP) {
+        if ((tselem->type != TSE_SOME_ID) && tselem->type != TSE_DEFGROUP) {
           tp->idcode = 0; /* Don't sort this. */
         }
         if (tselem->type == TSE_ID_BASE) {
@@ -1471,7 +1473,7 @@ static void outliner_collections_children_sort(ListBase *lb)
   TreeStoreElem *tselem = TREESTORE(te);
 
   /* Sorting rules: only object lists. */
-  if (tselem->type == 0 && te->idcode == ID_OB) {
+  if ((tselem->type == TSE_SOME_ID) && (te->idcode == ID_OB)) {
     int totelem = BLI_listbase_count(lb);
 
     if (totelem > 1) {
@@ -1546,7 +1548,7 @@ static bool test_collection_callback(TreeElement *te)
 static bool test_object_callback(TreeElement *te)
 {
   TreeStoreElem *tselem = TREESTORE(te);
-  return ((tselem->type == 0) && (te->idcode == ID_OB));
+  return ((tselem->type == TSE_SOME_ID) && (te->idcode == ID_OB));
 }
 
 /**
@@ -1707,7 +1709,7 @@ static bool outliner_element_visible_get(ViewLayer *view_layer,
   }
 
   TreeStoreElem *tselem = TREESTORE(te);
-  if ((tselem->type == 0) && (te->idcode == ID_OB)) {
+  if ((tselem->type == TSE_SOME_ID) && (te->idcode == ID_OB)) {
     if ((exclude_filter & SO_FILTER_OB_TYPE) == SO_FILTER_OB_TYPE) {
       return false;
     }
@@ -1790,14 +1792,15 @@ static bool outliner_element_visible_get(ViewLayer *view_layer,
       return is_visible;
     }
 
-    if ((te->parent != NULL) && (TREESTORE(te->parent)->type == 0) &&
+    if ((te->parent != NULL) && (TREESTORE(te->parent)->type == TSE_SOME_ID) &&
         (te->parent->idcode == ID_OB)) {
       if (exclude_filter & SO_FILTER_NO_CHILDREN) {
         return false;
       }
     }
   }
-  else if (te->parent != NULL && TREESTORE(te->parent)->type == 0 && te->parent->idcode == ID_OB) {
+  else if ((te->parent != NULL) && (TREESTORE(te->parent)->type == TSE_SOME_ID) &&
+           (te->parent->idcode == ID_OB)) {
     if (exclude_filter & SO_FILTER_NO_OB_CONTENT) {
       return false;
     }
@@ -1821,7 +1824,7 @@ static bool outliner_element_is_collection_or_object(TreeElement *te)
 {
   TreeStoreElem *tselem = TREESTORE(te);
 
-  if ((tselem->type == 0) && (te->idcode == ID_OB)) {
+  if ((tselem->type == TSE_SOME_ID) && (te->idcode == ID_OB)) {
     return true;
   }