-P '\d' in GNU and git grep

[Paul Eggert <eggert@cs.ucla.edu>]

I've recently done some bug-report maintenance about a set of GNU grep 
bug reports related to whether whether "grep -P '\d'" should match 
non-ASCII digits, and have some thoughts about coordinating GNU grep 
with git grep in this department.

GNU Bug#62605[1] "`[\d]` does not work with PCRE" has been fixed on 
Savannah's copy of GNU grep, and some sort of fix should appear in the 
next grep release. However, I'm leaving the GNU grep bug report open for 
now because it's related to Bug#60690[2] "[PATCH v2] grep: correctly 
identify utf-8 characters with \{b,w} in -P" and to Bug#62552[3] "Bug 
found in latest stable release v3.10 of grep". I merged these related 
bug reports, and the oldest one, Bug#60690, is now the representative 
displayed in the GNU grep bug list[4].

For this set of grep bug reports there's still a pending issue discussed 
in my recent email[5], which proposes a patch so I've tagged Bug#60690 
with "patch". The proposal is that GNU grep -P '\d' should revert to the 
grep 3.9 behavior, i.e., that in a UTF-8 locale, \d should also match 
non-ASCII decimal digits.

In researching this a bit further, I found that on March 23 Git disabled 
the use of PCRE2_UCP in PCRE2 10.34 or earlier[6], due to a PCRE2 bug 
that can cause a crash when PCRE2_UCP is used[7]. A bug fix[8] should 
appear in the next PCRE2 release.

When PCRE2 10.35 comes out, it appears that 'git grep -P' will behave 
like 'grep -P' only if GNU grep adopts something like the solution 
proposed in [5].

[1]: https://bugs.gnu.org/62605
[2]: https://bugs.gnu.org/60690
[3]: https://bugs.gnu.org/62552
[4]: https://debbugs.gnu.org/cgi/pkgreport.cgi?package=grep
[5]: https://lists.gnu.org/archive/html/grep-devel/2023-04/msg00004.html
[6]: 
https://github.com/git/git/commit/14b9a044798ebb3858a1f1a1377309a3d6054ac8
[7]: 
https://lore.kernel.org/git/7E83DAA1-F9A9-4151-8D07-D80EA6D59EEA@clumio.com/
[8]: 
https://github.com/git/git/commit/14b9a044798ebb3858a1f1a1377309a3d6054ac8