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bug#47264: [PATCH v2] pcre: migrate to pcre2

From: Paul Eggert
Subject: bug#47264: [PATCH v2] pcre: migrate to pcre2
Date: Sun, 14 Nov 2021 19:17:58 -0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.1

On 11/14/21 14:25, Carlo Arenas wrote:

the one in patch6 where a uint32_t option is doubled, triggers
warnings because of comparing an unsigned variable with 0 AFAIK, but
there are several of those in the upstream gnulib so presumably not a

Yes, that's right. intprops.h can generate tons of bogus warnings with older or non-GCC compilers. We typically don't worry about those warnings. Recent GCC should be OK here.

using idx_t instead of size_t should be fine (if only halves the max
size of the objects managed), but I am concerned that assuming
PCRE2_SIZE_MAX is always equivalent to SIZE_MAX (as done in patch 4)
might be risky (at least without a comment), and considering that is
part of the API anyway might be better if kept as PCRE2_SIZE_MAX IMHO.

This shouldn't be a problem in practice. Surely PCRE2_SIZE_MAX is for forward compatibility to a potential future version of PCRE2 that may define PCRE2_SIZE to be some other type. For PCRE2 10.20 and earlier PCRE2_SIZE is hardwired to size_t, so there is only one plausible default for PCRE2_SIZE_MAX, namely SIZE_MAX.

As I mentioned before, PCRE matches the Perl definition as mentioned
before in an early draft that also had this change reversed.

I see that PCRE2 documents that PCRE2_EXTRA_MATCH_WORD surrounds the pattern with "\b(?:" and ")\b". However, this is bogus: it doesn't correspond to the intuitive meaning of "match words", and it doesn't correspond to how grep -w behaves for any grep that I know of.

Which "early draft" are you talking about? This appears to be merely a bug in libpcre2's documentation and implementation.

I would suggest instead that -P should also follow perl convention
instead when used together with -w, but maybe that is something that a
-P feature flag could enable or disable as needed?

I can't imagine anybody intuitively saying in an English locale that "%%" is a word in the string "aa%%aa". PCRE2 is broken, that's all. If a user really wants PCRE2's buggy interpretation, they can simply surround their regexp with "\b(?:" and ")\b" and not use -w; so there's no need to have a different flag for pcre2grep's bizarre interpretation of -w.

Here's another reason why pcre2grep -w is obviously busted:

$ pcre2grep -w ',' <<'EOF'
> a,a
> a, a
> a,

Why is "," a word in the first input line, but not in the second or third? pcre2grep is simply wrong here.

Note that "word" definition also has a different meaning in a post
Unicode world

Yes, but that's an independent issue.

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