bug#64204: closed (C/C++ local variables not syntax highlighted if they start with $)

[GNU bug Tracking System]

Your message dated Wed, 28 Jun 2023 18:45:09 +0000
with message-id <ZJx_tZu8KmhZvbWG@ACM>
and subject line Re: bug#64204: C/C++ local variables not syntax highlighted if 
they start with $
has caused the debbugs.gnu.org bug report #64204,
regarding C/C++ local variables not syntax highlighted if they start with $
to be marked as done.

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64204: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=64204
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--- Begin Message --- Subject: C/C++ local variables not syntax highlighted if they start with $ Date: Tue, 20 Jun 2023 15:54:52 -0500

Start emacs with `emacs -Q`, press C-x C-f and type in a filename that
ends in .cpp like "foo.cpp". Then type in:

int main()
{
    int a = 0;
    int b = 0;
    int $ = 0;
    int d$ = 0;
    int $e = 0;
}

Yes it compiles! GCC, Clang, and MSVC all have a non-standard

extension that allows $ signs to appear in C/C++ variable and type

names: https://gcc.gnu.org/onlinedocs/gcc/Dollar-Signs.html

Then a,b,d$ will be highlighted correctly as local vars, but not $ or
$e. The highlighting doesn't appear to work whenever $ is the first or
only character. Since emacs is accepting of the $ sign anywhere else in
the variable name, I suspect supporting $ was intended, even though it's
non-standard. Even if not intended, it's a popular syntax
extension supported by the major current compilers and whose history
goes back to the DEC compiler, so support would be nice.

In GNU Emacs 28.0.50 (build 1, x86_64-pc-linux-gnu, X toolkit, cairo version 1.16.0, Xaw3d scroll bars)
 of 2021-05-14 built on eruv
Repository revision: efc24f1e0bb127481bcc9c3054c57c4cd3c99aa9
Repository branch: master
Windowing system distributor 'The X.Org Foundation', version 11.0.12013000
System Description: Ubuntu 20.04.6 LTS

--- End Message ---

> --- Begin Message ---
>
>
>
> Subject: 
>
> Re: bug#64204: C/C++ local variables not syntax highlighted if they start with $
>
>
>
>
> Date: 
>
> Wed, 28 Jun 2023 18:45:09 +0000
>
>
>
>
> Hello, Joseph and Eli.
>
> On Thu, Jun 22, 2023 at 13:13:59 +0300, Eli Zaretskii wrote:
> > > Date: Thu, 22 Jun 2023 09:11:38 +0000
> > > Cc: luangruo@yahoo.com, 64204@debbugs.gnu.org
> > > From: Alan Mackenzie <acm@muc.de>
>
> > > > Thanks, but shouldn't this be optional behavior, which users should be
> > > > able to control?  Standard C disallows '$' in identifiers AFAIK, and
> > > > some users might wish to follow the Standard.
>
> > > The thing is, such an option would be difficult to implement.  At the
> > > moment, c-symbol-start and c-symbol-key (regular expressions which match
> > > the start of an identifier and all of one) are calculated in cc-langs.el
> > > at compilation time.  They are widely used (~40 times) in the indentation
> > > engine and fontification.
>
> > > It would be necessary to change these constants to variables, probably
> > > doubling the number of relevant c-lang-const's in cc-langs.el, and to add
> > > a mechanism to toggle between them at run time.
>
> > > I don't feel that the benefit from this new option would really be worth
> > > the work it would take to implement.
>
> > I do feel it's worth the effort.  If we value correct fontification,
> > of course.  I don't know what my opinions on this mean for you, but
> > there you have it.  I cannot force you make this change, of course, I
> > can only try to convince.
>
> :-)  OK, the fontification of identifiers with $ is now working.  By
> default they are fontified as normal identifiers (i.e. with
> font-lock-type-face, font-lock-variable-name-face, or
> font-lock-function-name-face), but if the (new) customisable option
> c-warn-ids-with-dollar is set to non-nil, font-lock-warning-face is used
> instead.  The above applies only to C, C++, and Objective C Modes, and to
> any derived modes which enable the mechanism.
>
> So, I'm closing the bug now with this post.
>
> -- 
> Alan Mackenzie (Nuremberg, Germany).
>
>
> --- End Message ---