Re: [PATCH] grep: skip UTF8 checks explicitally

From: Johannes Schindelin <Johannes.Schindelin@gmx.de>
To: Junio C Hamano <gitster@pobox.com>
Cc: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Carlo Arenas" <carenas@gmail.com>,
	git@vger.kernel.org
Subject: Re: [PATCH] grep: skip UTF8 checks explicitally
Date: Thu, 25 Jul 2019 11:48:16 +0200 (CEST)	[thread overview]
Message-ID: <nycvar.QRO.7.76.6.1907251143430.21907@tvgsbejvaqbjf.bet> (raw)
In-Reply-To: <xmqqpnlzqh3d.fsf@gitster-ct.c.googlers.com>

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Hi,

On Wed, 24 Jul 2019, Junio C Hamano wrote:

> Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:
>
> > The PCRE2_NO_UTF_CHECK flag means "I have checked that this is a valid
> > UTF-8 string so you, PCRE, don't need to re-check it".
>
> OK, in short, barfing and stopping is a problem, but that flag is
> not the right knob to tweak.  And the right knob ...
>
> >  1) We're oversupplying PCRE2_UTF now, and one such case is what's being
> >     reported here. I.e. there's no reason I can think of for why a
> >     fixed-string pattern should need PCRE2_UTF set when not combined
> >     with --ignore-case. We can just not do that, but maybe I'm missing
> >     something there.
> >
> >  2) We can do "try utf8, and fallback". A more advanced version of this
> >     is what the new PCRE2_MATCH_INVALID_UTF flag (mentioned upthread)
> >     does. I was thinking something closer to just carrying two compiled
> >     patterns, and falling back on the ~PCRE2_UTF one if we get a
> >     PCRE2_ERROR_UTF8_* error.
>
> ... lies somewhere along that line.  I think that is very sensible.

I am glad that everybody agrees with my original comment on ab/no-kwset
where I suggested that we should use our knowledge of the encoding of
the haystack and convert it to UTF-8 if we detect that the pattern is
UTF-8 encoded, and then pass the PCRE2_UTF flag only when applicable
(i.e. when we know that either needle or haystack is non-ASCII, and then
making sure that we convert to UTF-8 whenever necessary).

Okay, that came over a bit more sarcastic than I originally intended,
but if you try to filter that out, I think that is still the better
solution than to paper over the issue.

After all, PCRE2_MATCH_INVALID_UTF is only marginally better than what
Carlo suggested. _Marginally_. Not really worth considering, in my mind,
even.

> Let's make sure this gets sorted out soonish.

I agree,
Dscho