Chiming in with my minor voice. I prefer my mode configurations generally
self contained and not centralized as a single global configuration
variable would encourage. When I share my configurations with others, it
also suggests that if they adopt a global configuration variable on top of
what I share, it will introduce subtle changes in behavior that I may not
at first understand the source of when helping others. I definitely prefer
proper lisp over an opaque configuration variable.

-Stephane

On Fri, Nov 29, 2024 at 12:04 PM Stefan Monnier <monnier@iro.umontreal.ca>
wrote:

> > Since Emacs 29, I see many people ask about how to configure
> > tree-sitter modes by setting some variable.
>
> This is not specific to tree-sitter.
>
> > It seems that people much prefer setting a variable than adding
> > a major mode hook that calls some functions.
>
> But that boxes them into the subset of possibilities that have been
> pre-imagined by those who designed the set of variables.
>
> > What do you guys think about something like this:
> >
> > (setq treesit-global-configuration
> >       '((c-ts-mode
> >          ;; Set treesit-font-lock-level to 4
> >          (font-lock-level . 4)
> >          ;; Disable tree-sitter’s outline support
> >          (outline . disable)
> >          ;; Enable these features on top of the default ones.
> >          (font-lock-enable . (function property variable))
> >          ;; Disable these features.
> >          (font-lock-disable . (definition))
> >          ;; Add extra font-lock rules
> >          (font-lock-extra-rules
> >           ( :feature 'my-rules
> >             :language 'c
> >             ((some_query) @some-face)))
> >          (simple-indent-extra-rules
> >           (c
> >            (matcher anchor offset))
> >           (d
> >            (matcher anchor offset)))
> >          )))
>
> Sounds to me like this is inventing a new programming language, just one
> that's a lot more restrictive than ELisp.
>
> Is it really better than ELisp which could look like:
>
>     (add-hook 'c-ts-mode-hook #'my-c-ts-mode-preferences)
>     (defun my-c-ts-mode-preferences ()
>       (setq-local treesit-font-lock-level 4)
>       (treesit-outline-mode -1)
>       (treesit-font-lock-enable '(function property variable))
>       (treesit-font-lock-disable '(definition))
>       (treesit-font-lock-add-rules
>        '( :feature 'my-rules
>           :language 'c
>           ((some_query) @some-face)))
>       (treesit-indent-add-rules
>        '((c
>           (matcher anchor offset))
>          (d
>           (matcher anchor offset)))
>       ))
>
> Admittedly, the add-hook/defun dance could be improved, and that would
> benefit more than just tree-sitter.  E.g. a new macro like
>
>     (defmacro custom-set-hook (hook &rest body)
>       (declare (indent 1) (debug (sexp def-body)))
>       (let ((funname (intern (format "custom-set-hook--%s" hook))))
>         `(progn (add-hook ',hook #',funnmame)
>                 (defun ,funname () ,@body))))
>
> > One thing I don’t like is how it handles languages. In this POC
> > language-specific settings are nested under the mode. I’m ok with
> > mode-language hierarchy, but the nesting adds a lot of nesting levels
> > to the variable.  And the language nesting isn’t consistent, some
> > settings have language nesting, some don’t.
>
> I don't really understand what you're referring to, but for
> `treesit-font-lock-add-rules` would could try and auto-add the `:language`?
>
>
>         Stefan
>
>
>