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

From: Paul Eggert <[email-masked]>
Date: Mon, 9 Jan 2023 15:12:23 -0800

On 1/9/23 11:51, Ævar Arnfjörð Bjarmason wrote:

> 	/b:
> 	155781
> 	(*UCP)/b:
> 	46035
> 	/s:
> 	0
> 	(*UCP)/s:
> 	0
> 	/w:
> 	142468
> 	(*UCP)/w:
> 	9706
> 
> So the output still differs, and some of those differences may or may
> not be wanted.

I took a look at the output, and by and large I'd want the differences; 
that is, I'd want the UCP version, which generates less output. This is 
because several Emacs source files are not UTF-8, and \b has nonsense 
matches when searching text files encoded via Shift-JIS or Big 5 or 
whatever. For this sort of thing, the fewer matches the better.

> If all you're doing is matching either ASCII or Japanese text and you
> want "locale-aware numbers" it might do the wrong thing.

I'm not seeing much of a problem here. When searching Japanese text, I 
would expect \d and [0-9０-９] (using both ASCII and full-width digits) to 
be equivalent so (assuming UCP) it's not a big deal as to which regex 
you use, since Japanese text won't contain Bengali (or whatever) digits. 
And when searching binary data, I'd expect a bunch of garbage no matter 
how \d is interpreted.

Here I'm assuming [０-９] (using full-width digits) has the expected 
meaning in PCRE2, i.e., that PCRE2 didn't make the same mistake that 
POSIX made.