bug#68824: treesitter support for outline-minor-mode

[Eli Zaretskii <eliz@gnu.org>]

> Cc: Yuan Fu <casouri@gmail.com>
> From: Juri Linkov <juri@linkov.net>
> Date: Tue, 30 Jan 2024 19:37:20 +0200
> 
> As discussed on https://lists.gnu.org/archive/html/emacs-devel/2024-01/msg00916.html
> here is the patch that adds the support for outline-minor-mode to treesit.el.
> It has been tested on c-ts-mode, dockerfile-ts-mode, elixir-ts-mode, heex-ts-mode,
> java-ts-mode, js-ts-mode, typescript-ts-mode, css-ts-mode, html-ts-mode, toml-ts-mode.

Thanks, but shouldn't this minor mode be documented more prominently
in the Emacs user manual, now that there are so many major modes that
support it?  And since major modes that want to support it have to set
up its support, I would say the ELisp manual should document that
setup.

IOW, it makes little sense to make this minor mode more and more
prolific in Emacs, and still have almost nothing about it in our
manuals.

> +*** 'outline-minor-mode' is supported in tree-sitter major modes.
> +It can be used in all tree-sitter major modes that set either the
> +variable 'treesit-simple-imenu-settings' or 'treesit-outline-predicate'.

This terse description is okay, if the ELisp manual describes these
setups in more detail; alone it is insufficient.

> +(defvar-local treesit-outline-predicate nil
> +  "Predicate used to find outline headings in a sparse tree.

How do "sparse trees" enter the scene here?  AFAICS, "sparse trees" is
mentioned only once in the entire chapter dedicated to Tree Sitter
support in the ELisp manual.  Is it important to mention here the fact
that the tree is sparse?

> diff --git a/lisp/progmodes/heex-ts-mode.el b/lisp/progmodes/heex-ts-mode.el
> index 7b53a44deb2..23e2afbaaca 100644
> --- a/lisp/progmodes/heex-ts-mode.el
> +++ b/lisp/progmodes/heex-ts-mode.el
> @@ -166,6 +166,12 @@ heex-ts-mode
>                    ("Slot" "\\`slot\\'" nil nil)
>                    ("Tag" "\\`tag\\'" nil nil)))
>  
> +    ;; Outline minor mode
> +    ;; Restore default value for `treesit-outline-search'.
> +    (kill-local-variable 'outline-regexp)
> +    (kill-local-variable 'outline-heading-end-regexp)
> +    (kill-local-variable 'outline-level)

This mode seems to do something to support outline-minor-mode that is
not mentioned in the NEWS entry, and neither is treesit-outline-search.