Advice on this will be appreciated.

Someone pointed out to me on the legacy heex-ts-mode package on github that heex-ts-mode makes more sense to derive from prog-mode than html-mode.

Here is the comment: https://github.com/wkirschbaum/heex-ts-mode/issues/4 which reads:

"

The derivation chain goes heex-ts-mode <- html-mode <- sgml-mode <- text-mode <- nil. Which means users may trigger (and conversely not trigger) behavior they have setup in text-mode (and conversely prog-mode).

For a concrete example, the default completion-at-point keybinding is taken over by ispell in text-mode. This was unexpected since heex-ts-mode, is primarily a programming buffer, even if you're just mostly writing templates.

What are your thoughts on making it derive from prog-mode or web-mode rather than html-mode?

"

I think I agree, as HEEx is just Elixir looking like some html syntax. Language servers and other tools should treat this as Elixir, not text. Testing this change on my side with a very light setup shows that it has no negative impact. The wider impact of such a change is unknown to me.

The original decision for deriving from html-mode was because I followed how erb-mode ( ruby markup ) works, which might have been a mistake.

This is the proposed change:

---
 lisp/progmodes/heex-ts-mode.el | 12 +-----------
 1 file changed, 1 insertion(+), 11 deletions(-)

diff --git a/lisp/progmodes/heex-ts-mode.el b/lisp/progmodes/heex-ts-mode.el
index b527d96b579..ab40d4819e8 100644
--- a/lisp/progmodes/heex-ts-mode.el
+++ b/lisp/progmodes/heex-ts-mode.el
@@ -143,7 +143,7 @@ heex-ts--forward-sexp
    (abs arg)))
 
 ;;;###autoload
-(define-derived-mode heex-ts-mode html-mode "HEEx"
+(define-derived-mode heex-ts-mode prog-mode "HEEx"
   "Major mode for editing HEEx, powered by tree-sitter."
   :group 'heex-ts
 
@@ -168,16 +168,6 @@ heex-ts-mode
                   ("Slot" "\\`slot\\'" nil nil)
                   ("Tag" "\\`tag\\'" nil nil)))
 
-    ;; Outline minor mode
-    ;; `heex-ts-mode' inherits from `html-mode' that sets
-    ;; regexp-based outline variables.  So need to restore
-    ;; the default values of outline variables to be able
-    ;; to use `treesit-outline-predicate' derived
-    ;; from `treesit-simple-imenu-settings' above.
-    (kill-local-variable 'outline-heading-end-regexp)
-    (kill-local-variable 'outline-regexp)
-    (kill-local-variable 'outline-level)
-
     (setq-local treesit-font-lock-settings heex-ts--font-lock-settings)
 
     (setq-local treesit-simple-indent-rules heex-ts--indent-rules)
--

Wilhelm