bug#61655: [Tree sitter] [Feature Request] font-lock function calls, definitions, separately

[Yuan Fu <casouri@gmail.com>]

Jacob Faibussowitsch <jacob.fai@gmail.com> writes:

> Hello,
>
> Is it possible to have the builtin tree sitter give differentiate font-locking for function calls and function definitions?
>
> The 3rd party tree-sitter package (https://github.com/emacs-tree-sitter/elisp-tree-sitter) has this feature and it is quite
> nice. In fact it goes further, allowing you to additionally distinguish between builtin calls, macro calls, method calls, etc.
> (see https://github.com/emacs-tree-sitter/elisp-tree-sitter/blob/master/lisp/tree-sitter-hl.el).
>
> As far as I could see, the builtin mode only provides `font-lock-function-name-face`. I have set treesit-font-lock-level to
> 4. 
>
> Examples below are for C/C++ mode, but this would apply to any number of languages.
>
> Desired (i.e. what 3rd party package produces):
>
> *
>
> Current:
>
> *

Hmmm, yeah. The builtin tree-sitter maps syntax queries directly into
faces, where the third-party tree-sitter maps syntax queries to some
syntax types, then maps types to faces. So it would be a bit harder to
do fine-grained control like in the builtin tree-sitter, comparing to
the third-party one.

I’ve thought of this idea before but didn’t pursue it further: Right now
we allow capture names to be face names and functions, eg

(commment) @font-lock-comment-face

or

(comment) @xxx-moode-fortify-comment

Maybe we can add a third type, arbitrary symbols, like

(comment) @comment

and add a variables treesit-font-lock-mapping which maps symbols to
faces or functions:

((comment . font-lock-comment-face))

or

((comment . xxx-mode-fontify-comment))

Then we can easily support differentiating between function call and
function definition.

Yuan