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Date: Mon, 10 Jun 2024 11:56:14 -0400
From: Rich Felker <dalias@...c.org>
To: Valery Ushakov <uwe@...err.spb.ru>
Cc: musl@...ts.openwall.com, Nigel Kukard <nkukard@...D.net>
Subject: Re: Re: Different results with regex.h between Musl and Libc
On Mon, Jun 10, 2024 at 02:47:04PM +0300, Valery Ushakov wrote:
> On Mon, Jun 10, 2024 at 05:38:36 +0000, Nigel Kukard wrote:
>
> > Musl output (Alpine 3.20), musl-1.2.5-r1...
> >
> > The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
> > Match 0: 37
> > Match 1:
> > Match 2: 37
> >
> > Glibc output (ArchLinux), glibc 2.39+r52+gf8e4623421-1...
> >
> > The input '37' matches the pattern '^([0-9]*)?\.?([0-9]*)?$'
> > Match 0: 37
> > Match 1: 37
> > Match 2:
>
> I'm not sure what POSIX requires here. The closest I can find after
> skimming through "9. Regular Expressions" is 9.4.6 that ends with:
>
> An ERE matching a single character repeated by an '*', '?', or an
> interval expression shall not match a null expression unless this is
> the only match for the repetition or it is necessary to satisfy the
> exact or minimum number of occurrences for the interval expression.
>
> https://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap09.html#tag_09_04_06
>
> I'm not sure what to read into the absense of the usual "or an ERE
> enclosed in parentheses" chorus here.
This looks like a bug. The general requirement (from memory; I don't
have the spec in front of me now) is that each subexpression, in order
from the beginning of the regex, matches the maximal-length input it
can, subject to the overall constraint that the entire regex match the
earliest (first priority) and maximal length (second priority) input
it can.
I guess we need to dig into why this is happening, ensure it's
actually incorrect, and figure out how to fix it...
Rich
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