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

From: René Scharfe <l.s.r@web.de>
Date: Mar 27, 2023, 17:23 UTC
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:

Show 11 quoted lines

> 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/