On 2023-04-04 12:31, Junio C Hamano wrote:
My personal inclination is to let Perl folks decide
and follow them (even though I am skeptical about the wisdom of
letting '\d' match anything other than [0-9])
I looked into what pcre2grep does. It has always done only 8-bit
processing unless you use the -u or --utf option, so plain "pcre2grep
'\d'" matches only ASCII digits.
Although this causes pcre2grep to mishandle Unicode characters:
$ echo 'Ævar' | pcre2grep '[Ssß]'
Ævar
it mimics Perl 5.36:
$ echo 'Ævar' | perl -ne 'print $_ if /[Ssß]/'
Ævar
so this seems to be what Perl users expect, despite its infelicities.
For better Unicode handling one can use pcre2grep's -u or --utf option,
which causes pcre2grep to behave more like GNU grep -P and git grep -P:
"echo 'Ævar' | pcre2grep -u '[Ssß]'" outputs nothing, which I think is
what most people would expect (unless they're Perl users :-).
Neither git grep -P nor the current release of pcre2grep -u have \d
matching non-ASCII digits, because they do not use PCRE2_UCP. However,
in a February 8 commit[1], Philip Hazel changed pcre2grep to use
PCRE2_UCP, so this will mean 10.43 pcre2grep -u will behave like 3.9 GNU
grep -P did (though 3.10 has changed this).
That February commit also added a --no-ucp option, to disable PCRE2_UCP.
So as I understand it, if you're in a UTF-8 locale:
* 10.43 pcre2grep -u will behave like 3.9 GNU grep -P.
* 10.43 pcre2grep -u --no-ucp will behave like git grep -P.
* Current GNU grep -P is different from everybody else.
This incompatibility is not good.
Here are two ways forward to fix this incompatibility (there are other
possibilities of course):
(A) GNU grep adds a --no-ucp option that acts like 10.43 pcre2grep
--no-ucp, and git grep -P follows suit. That is, both GNU and git grep
act like 10.43 pcre2grep -u, in that they enable PCRE2_UTF, and also
enable PCRE2_UCP unless --no-ucp is given. This would cause \d to match
non-ASCII digits unless --no-ucp is given.
(B) GNU grep -P and git grep -P mimic pcre2grep in both -u and --no-ucp.
That is, they would both do 8-bit-only by default, and use PCRE2_UTF
only when -u or --utf is given, and use PCRE2_UCP only when --no-ucp is
absent. This would cause \d to match non-ASCII digits only when -u is
given but --no-ucp is not.
Under either (A) or (B), future pcre2grep -u, GNU grep -P, and git grep
-P would be consistent.
I mildly prefer (B) but (A) would also work. (One advantage of (B) is
that it should be faster....)
[1]:
https://github.com/PCRE2Project/pcre2/commit/8385df8c97b6f8069a48e600c7e4e94cc3e3ebd9ht
