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

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Message #11 received at 61144 <at> debbugs.gnu.org (full text, mbox):

From: Po Lu <luangruo <at> yahoo.com>
To: Alan Mackenzie <acm <at> muc.de>
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: Tue, 31 Jan 2023 09:23:01 +0800

Alan Mackenzie <acm <at> muc.de> writes:

> 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!
>
> [ .... ]

Thank you, this works here.

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