From: "Dmitry V. Levin" <ldv@altlinux.org>
To: Egor Ignatov <egori@altlinux.org>
Cc: Paul Eggert <eggert@cs.ucla.edu>, bug-gnulib@gnu.org
Subject: Re: [PATCH] regex: fix backreference matching
Date: Mon, 5 Jul 2021 15:12:02 +0300 [thread overview]
Message-ID: <20210705121201.GA20072@altlinux.org> (raw)
In-Reply-To: <85975173-4e58-1402-00c8-8d065b967f99@altlinux.org>
On Tue, Jun 29, 2021 at 11:51:13AM +0300, Egor Ignatov wrote:
> Well, then I have a few questions about matching and capturing
> groups.
>
> 1. "ab" -> "^(a*)*(.)"
> So, from your test case I can assume that:
> regs[0] = (0, 2]
> regs[1] = (0, 1]
> regs[2] = (1, 2]
>
> But if we add backref at the end:
> 2. "ab" -> "^(a*)*(.)\1"
> check_matching matches the whole string "ab",
> this means that the first group accepted 'a' but in fact is empty,
> otherwise it could not match backref later on.
> What is the correct match here? Is check_matching wrong and
> should match only "a" in the 2nd group (as it would be with
> "^(a*)(.)\1")? or should set_regs check for this and shrink the
> match?
My test-regex.c entry for a similar but a bit simplified case was:
/* Test for ** match with backreferences. */
{ "^(a*)*\\1", "a", REG_EXTENDED, 2, { { 0, 0 }, { 0, 0 } } }
I suppose the corresponding entry for your example would be
{ "^(a*)*(.)\1", "ab", REG_EXTENDED, 3, { { 0, 1 }, { 0, 0 }, { 0, 1 } } }
> Next,
> 3. "aaba" -> "^(a*)*(.)\1"
> Again check_matching matches "aaba", then the first group
> is "a", and were the 2nd 'a' goes?
I suppose the corresponding test-regex.c entry for this case would be
{ "^(a*)*(.)\1", "aaba", REG_EXTENDED, 3, { { 0, 4 }, { 0, 1 }, { 2, 3 } } }
--
ldv
next prev parent reply other threads:[~2021-07-05 12:12 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-26 9:08 [PATCH] regex: fix match with possessive quantifier Egor Ignatov
2021-06-06 21:45 ` Dmitry V. Levin
2021-06-07 1:10 ` Dmitry V. Levin
2021-06-16 9:46 ` [PATCH] regex: fix backreference matching Egor Ignatov
2021-06-16 10:13 ` Dmitry V. Levin
2021-06-29 8:51 ` Egor Ignatov
2021-07-05 12:12 ` Dmitry V. Levin [this message]
2021-07-09 12:36 ` [PATCH v2] " Egor Ignatov
2021-06-16 10:18 ` [PATCH] regex: fix match with possessive quantifier Dmitry V. Levin
2021-06-21 21:09 ` Paul Eggert
2021-06-22 15:35 ` Egor Ignatov
2021-06-22 15:35 ` [PATCH] regex: fix assertion in re_node_set_insert Egor Ignatov
2021-06-22 19:41 ` Paul Eggert
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
List information: https://lists.gnu.org/mailman/listinfo/bug-gnulib
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20210705121201.GA20072@altlinux.org \
--to=ldv@altlinux.org \
--cc=bug-gnulib@gnu.org \
--cc=eggert@cs.ucla.edu \
--cc=egori@altlinux.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).