Re: git bug: Perl compatible regular expressions do not work as expected

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 27, 2023, 16:29 UTC
Message-ID: <xmqqh6u6cg4l.fsf@gitster.g>
In-Reply-To: <eba23dc4-c036-fd1b-a1f0-028e8fff602b@web.de>

René Scharfe <l.s.r@web.de> writes:

Show 12 quoted lines

> Am 25.03.23 um 14:09 schrieb Mario Grgic:
>> The lowercase -p is to print the output in patch format. You can rewrite the command line as
>>
>>  git log --all --patch --perl-regexp -G '\bmain\b’
>>
>> I still get no output in any git version after 2.38.4
>
> -G doesn't support Perl regular expressions.  --perl-regexp only affects
> --grep, --grep-reflog, --author, and --committer.  Neither POSIX basic
> nor extended regular expressions support \b as word boundary.  GNU regex
> and our compat/regex/ do, as extensions.  macOS regex supports it if the
> flag REG_ENHANCED is given to regcomp(3).

Good summary to unconfuse speculations in the thread.

> So perhaps this is rather a feature request to support Perl regular
> expressions for -G (and probably -S as well).

Perhaps. I used to be a "it would be wonderful if pcre were usable everywhere" dreamer, but after seeing our share of bugs caused by use of pcre, I am not a huge proponent anymore. I do not object to such an enhancement at all, as long as it is done cleanly and in such a way that it is clear pcre cannot be used by accident when the user does not ask for it.

> Or to enable REG_ENHANCED
> for them, at least, like 54463d32ef (use enhanced basic regular
> expressions on macOS, 2023-01-08) did to get alternations for git grep
> on macOS.

This one sounds like a reasonable thing, which may not have huge unintended fallout, to do. I am a bit surprised that we have to cover each individual callsite of regcomp(3), though. Doesn't the 54463d32ef fix use "#define regcomp git_regcomp" to cover everybody?