From: René Scharfe <l.s.r@web.de>
Date: Mon, 27 Mar 2023 17:23:35 GMT
Subject: Re: git bug: Perl compatible regular expressions do not work as expected
Message-ID: <03fd7ddb-8241-1a0a-3e82-d8083e4ce0f7@web.de>
In-Reply-To: <xmqqh6u6cg4l.fsf@gitster.g>

Am 27.03.23 um 18:29 schrieb Junio C Hamano:
> René Scharfe <l.s.r@web.de> writes:
>
>> 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?

54463d32ef only affects basic regular expressions (BRE), but -G and -S
use extended ones (ERE).  macOS allows both to be "enhanced".

I have a hard time finding a readable reference to the documentation to
brings us all onto the same page regarding what REG_ENHANCED actually
does.  [1] is in raw troff format, [2] isn't very pretty and shows ads.
Anyway, the rather lengthy section "ENHANCED FEATURES" explains it.

René


[1] https://opensource.apple.com/source/Libc/Libc-1439.40.11/regex/FreeBSD/re_format.7.auto.html
[2] https://www.unix.com/man-page/osx/7/re_format/