bug#63840: 29.0.91; c-ts-mode fails to fontify common C extension

[Eli Zaretskii <eliz@gnu.org>]

> From: Yuan Fu <casouri@gmail.com>
> Date: Sun, 18 Jun 2023 23:43:51 -0700
> Cc: Theodor Thornhill <theo@thornhill.no>,
>  Po Lu <luangruo@yahoo.com>,
>  63840@debbugs.gnu.org
> 
> > On Jun 15, 2023, at 11:31 PM, Eli Zaretskii <eliz@gnu.org> wrote:
> > 
> >> From: Yuan Fu <casouri@gmail.com>
> >> Date: Thu, 15 Jun 2023 22:05:33 -0700
> >> Cc: Theodor Thornhill <theo@thornhill.no>,
> >> Po Lu <luangruo@yahoo.com>,
> >> 63840@debbugs.gnu.org
> >> 
> >>> Ping!  Any progress with this?
> >> 
> >> The best option is to ask tree-sitter-c to recognize $. I see a PR for it but the author closed it shortly after posting, not sure what was going on[1].
> > 
> > Any hope of re-opening it, or at least asking why it was closed
> > without fixing?
> 
> I asked on GitHub.
> 
> > 
> >> Fixing it ourselves involves checking every identifier during fontification. Is that something we want to do?
> > 
> > How would that work?  Can you describe how could this be implemented?
> > It is hard to decide whether it's something we want to do without
> > knowing the implications.
> 
> I was going to write a demo implementation, but that actually would change quite some lines. So let me just describe it for now. In c-ts-mode--font-lock-settings, I would replace all the different types of faces used for all the identifiers to a function. (If you search for identifier in c-ts-mode--font-lock-settings, there are quite a few of them.) This function would obviously receive the beg and end of the identifier tree-sitter detects, and it would check if there are $ right before or after the given range, if there is, it would extend the range fontified.
> 
> For example, for a code like abc$de, tree-sitter might consider abc as an identifier, and $ de to be error. The function I mentioned would look at abc’s beg and end, and see that c is immediately followed by a $, so it would extend the fontification range to include abc$de.

Thanks.  This sounds like a lot of hair, so let's first see how the
developers of the tree-sitter-c grammar respond.