GNU bug report logs - #61144
CC Mode 5.35.2 (C/*l); Incorrect fontification (but different from last time)

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Message #8 received at 61144 <at> debbugs.gnu.org (full text, mbox):

From: Alan Mackenzie <acm <at> muc.de>
To: Po Lu <luangruo <at> yahoo.com>
Cc: 61144 <at> debbugs.gnu.org
Subject: Re: bug#61144: CC Mode 5.35.2 (C/*l); Incorrect fontification (but
 different from last time)
Date: Mon, 30 Jan 2023 21:53:11 +0000

[Message part 1 (text/plain, inline)]

Hello, Po.

On Sun, Jan 29, 2023 at 19:00:47 +0800, Po Lu via CC-Mode-help wrote:
> Package: cc-mode

> Emacs  : GNU Emacs 30.0.50 (build 41, x86_64-pc-linux-gnu)
>  of 2023-01-29
> Package: CC Mode 5.35.2 (C/*l)
> Buffer Style: gnu
> c-emacs-features: (pps-extended-state col-0-paren posix-char-classes gen-string-delim gen-comment-delim syntax-properties category-properties 1-bit)

> Insert the following text in a C Mode buffer:

> static sfnt_f26dot6
> sfnt_mul_f26dot6 (sfnt_f26dot6 a, sfnt_f26dot6 b)
> {
> #ifdef INT64_MAX
>   return (sfnt_f26dot6) ((int64_t) a * b + (1 << 5) >> 6);
> #else
>   int negative;
>   unsigned short al, bl, ah, bh;
>   unsigned int lowlong, midlong, hilong;

>   negative = 0;

>   /* Compensate for complement and determine if the result will be
>      negative.  */

>   if (a < 0)
>     {
>       a = -a;
>       negative = 1;
>     }

>   if (b < 0)
>     {
>       b = -b;
>       negative ^= true;
>     }

>   /* Load low and high words from A and B.  */
>   al = a & 0xffff;
>   bl = b & 0xffff;
>   ah = a >> 16;
>   bh = b >> 16;

>   /* Multiply the various bits separately.  */
>   midlong = (unsigned int) al * bh;
> #endif
> }

> In ``al * bh'', al is fontified as a type, and bh an identifier.

Yes.  foo * bar is a difficult case, since it can either be a
multiplication or a declaration of bar as a pointer to foo.  There is no
reliable way to distinguish these two cases without a full parser.  No
doubt c-ts-mode will do better here.

In another similar case, I have disambiguated these with "whitespace
asymmetry" - If there's WS both before and after the "*" or neither,
it's treated as a multiplication.  Otherwise it's a declaration.

I've extended this heuristic to treat the case in your test file.  Would
you try out the attached patch, please (it applies cleanly to the master
branch).  I would be in favour of putting the patch into the release
branch, but given the patch is ~90 lines long, Eli might object.

Anyhow, please try it out, and let me know what you think about it.
Thanks!

[ .... ]

-- 
Alan Mackenzie (Nuremberg, Germany).

[diff.20230130.diff (text/plain, attachment)]

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