GNU bug report logs - #64204
C/C++ local variables not syntax highlighted if they start with $

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From: help-debbugs <at> gnu.org (GNU bug Tracking System)
To: Joseph Garvin <k04jg02 <at> gmail.com>
Subject: bug#64204: closed (Re: bug#64204: C/C++ local variables not
 syntax highlighted if they start with $)
Date: Wed, 28 Jun 2023 18:46:03 +0000

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Your bug report

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

which was filed against the emacs package, has been closed.

The explanation is attached below, along with your original report.
If you require more details, please reply to 64204 <at> debbugs.gnu.org.

-- 
64204: https://debbugs.gnu.org/cgi/bugreport.cgi?bug=64204
GNU Bug Tracking System
Contact help-debbugs <at> gnu.org with problems

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From: Alan Mackenzie <acm <at> muc.de>
To: Eli Zaretskii <eliz <at> gnu.org>, Joseph Garvin <k04jg02 <at> gmail.com>
Cc: luangruo <at> yahoo.com, acm <at> muc.de, 64204-done <at> debbugs.gnu.org
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 <at> yahoo.com, 64204 <at> debbugs.gnu.org
> > From: Alan Mackenzie <acm <at> 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).

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From: Joseph Garvin <k04jg02 <at> gmail.com>
To: bug-gnu-emacs <at> gnu.org
Subject: C/C++ local variables not syntax highlighted if they start with $
Date: Tue, 20 Jun 2023 15:54:52 -0500

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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

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