GNU bug report logs - #60690
[PATCH v2] grep: correctly identify utf-8 characters with \{b,w} in -P

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From: Paul Eggert <eggert <at> cs.ucla.edu>
To: Carlo Arenas <carenas <at> gmail.com>
Cc: demerphq <demerphq <at> gmail.com>, pcre2-dev <at> googlegroups.com, 60690 <at> debbugs.gnu.org, mega lith01 <megalith01 <at> gmail.com>, Ævar Arnfjörð Bjarmason <avarab <at> gmail.com>, Junio C Hamano <gitster <at> pobox.com>, Tukusej’s Sirs <tukusejssirs <at> protonmail.com>, git <at> vger.kernel.org
Subject: bug#60690: -P '\d' in GNU and git grep
Date: Sat, 8 Apr 2023 15:45:20 -0700

On 2023-04-07 22:01, Carlo Arenas wrote:

> Not sure I follow the whole logic here, but PCRE2[3] (search for
> "general category" which is what the "gc" above stands for) only
> supports the abbreviated form of the unicode classes and `Nd` is
> indeed the one that corresponds to `Decimal_Number`.

That's fine: all that UTS#18[1] requires is that PCRE2 provide syntax 
for a regular expression that matches the Decimal Number class. Which 
PCRE2 does, via \p{Nd}.

The logic is that UTF#18 does not require that \d must behave like 
\p{Nd}, or even that \p{gc=Decimal_Number} must behave like \p{Nd}. It 
merely requires that there be some syntax for matching Decimal Number, 
and it says the choice of syntax is up to the implementer. This is why 
UTF#18 doesn't require that \d must also match non-ASCII digits (which 
is what I think Yves was saying).

[1]: https://unicode.org/reports/tr18/

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