In D13858#370369, @Julian Eisel (Severin) wrote:

• This needs versioning code so the highlight color works for preferences saved in earlier versions, see do_versions_theme().

Right, completely forgot about it, sorry.
I'll update the diff also including the various name changes.

• Since this also adds highlighting to list-rows, it has the same issue as noted here https://developer.blender.org/D12549#363450. I can look into this, but it should be addressed before or when this lands.

Ah, I didn't know about that other patch.
For this overlap problem I tried to expand ui_handle_tree_hover() to also manage this case too, but as @Harley Acheson (harley) already found, it doesn't seem to work as expected..

Between the two I would always favor a patch that simplifies (yours) over one that continues with the current mess (mine).

@Alessio Monti di Sopra (a.monti) - For this overlap problem I tried to expand ui_handle_tree_hover() to also manage this case too, but as @Harley Acheson (harley) already found, it doesn't seem to work as expected..

For completeness I also applied this patch and then added my attempt at fixing that child-item issue with ui_region_handler and had no luck. That basically looks like this:

static int ui_region_handler(bContext *C, const wmEvent *event, void *UNUSED(userdata))
{
  ...
  if (retval == WM_UI_HANDLER_CONTINUE && listbox) {

    uiBut *hovered_row = ui_list_row_find_mouse_over(region, event->xy);
    if (hovered_row) {
      hovered_row->flag |= UI_ACTIVE;
    }

    retval = ui_handle_list_event(C, event, region, listbox);
  ...

The above (roughly) matches what is happening for ui_handle_tree_hover, but a bit simpler. But still didn't work. LOL.

The above (roughly) matches what is happening for ui_handle_tree_hover, but a bit simpler. But still didn't work. LOL.

No idea.. What I did instead is to expand that function to include both the list and tree cases while keeping the same logic and, it doesn't work.
The only thing I noticed in debug is that the function gets executed a lot of times in a row with different "events" and slightly different cursor positions. Not sure if that is expected, as I'm definitely not familiar with that.

One other thing: to expand ui_handle_tree_hover()I wanted to change the first check to use UI_BLOCK_LIST_OR_TREE_ITEM, that's not possible though, as the flag gets disabled to avoid tagging for theme unwanted labels.

@Julian Eisel (Severin) @Harley Acheson (harley) The more I look at this system the more I hate it to be honest, I'm wondering if moving everything inside a single function (that manage both the theming flag and the set active part) would be better or not, something like this:

-void ui_layout_list_set_labels_active(uiLayout *layout)
+void ui_layout_list_or_tree_row_manage_labels(uiLayout *layout, bool active)
 {
   LISTBASE_FOREACH (uiButtonItem *, bitem, &layout->items) {
     if (bitem->item.type != ITEM_BUTTON) {
-      ui_layout_list_set_labels_active((uiLayout *)(&bitem->item));
+      ui_layout_list_or_tree_row_set_labels_active((uiLayout *)(&bitem->item), active);
     }
-    else if (bitem->but->flag & UI_BUT_LIST_ITEM) {
-      UI_but_flag_enable(bitem->but, UI_SELECT);
+    else if (ELEM(bitem->but->type, UI_BTYPE_LABEL, UI_BTYPE_TEXT)) {
+      UI_but_flag_enable(bitem->but, UI_BUT_LIST_OR_TREE_ITEM);
+      if (active) {
+        UI_but_flag_enable(bitem->but, UI_SELECT);
+      }
     }
   }
 }

and keep the block flag active for other checks.

In D13858#370369, @Julian Eisel (Severin) wrote:

@Pablo Vazquez (pablovazquez) do you think we should add own theme colors for tree-rows, or is it fine to share colors with list rows?

I think it's okay to use list row colors since it serves a similar purpose, look-alike, and we already have way too many theme settings.