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

[Yuan Fu <casouri@gmail.com>]

> On Jun 2, 2023, at 5:51 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
>> Date: Fri, 02 Jun 2023 20:11:33 +0800
>> From:  Po Lu via "Bug reports for GNU Emacs,
>> the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
>> 
>> A common extension to the C language is the use of the `$' sign inside
>> external identifier names.
>> 
>> This is permitted by GNU CC on most systems it supports, and also
>> supported by CC Mode.  However, it does not work on c-ts-mode:
>> 
>> sl$loadarena ()
>> {
>>  struct FAB fab;
>>  register int status;
>>  extern char *sl$dfname;
>> 
>>  fab = cc$rms_fab;
>>  fab.fab$b_fac = FAB$M_BIO | FAB$M_GET;
>>  fab.fab$l_fna = sl$dfname;
>>  fab.fab$b_fns = strlen (sl$dfname);
>>  status = sys$open (&fab);
>>  if (status != RMS$_NORMAL)
>>    return status;
>>  /* More code below.  */
>> }
>> 
>> in the identifier name of this function declarator, `sl' is fontified as
>> a type.  `$' is not fontified at all.  `loadarena' is fontified as an
>> identifier name, as it should be.  In:
>> 
>>  extern char *sl$defname;
>> 
>> only `dfname' is fontified as a variable name; in CC Mode, all
>> fontification is correct.
>> 
>> This should be a simple change in c-ts-mode's identifier fontifying
>> regexp to include `$', right?  I don't know enough about tree-sitter to
>> fix it myself.
> 
> I'm not sure this can be fixed unless the tree-sitter's C grammar
> supports such identifiers, but if we can fix it in our code, we
> should.
> 
> Yuan and Theo, can you please look into this?

Yeah. So is this the only way $ is used in C? Could it appear in contexts other than identifiers?

Yuan