Re: [PATCH] Fix for bug #19474: LIKE fails to match literal backslashes with nondeterministic collations

Hi Nitin,

Thanks for v3.

I re-applied it on top of current master (4cb2a986) and re-ran the
regression suite: all 245 tests pass, and the collate.icu.utf8 set now
covers both directions of the bug, including the false-positive case
('backslash' LIKE 'back\\slash%' -> f).

LGTM, and changed commitfest status to "Ready for Commiter".

Regards,
Ewan Young

On Sat, Jun 6, 2026 at 8:25 PM Nitin Motiani <nitinmotiani(at)google(dot)com> wrote:
>
> > I reviewed the v2 patch.
> >
>
> Thanks for the feedback.
>
> >
> > 1. The commit message describes the symptom as "an incorrect match
> > failure", but the bug also causes incorrect matches in the other
> > direction. Since the unescaping logic dropped the literal backslash
> > from the pattern, a text *without* a backslash could wrongly match a
> > pattern that requires one:
> >
> > SELECT 'backslash' COLLATE ignore_accents LIKE 'back\\slash%';
> > -- unpatched: t (wrong), patched: f (correct)
> >
> > I think it's worth mentioning this false-positive side of the bug in
> > the commit message, since silently-too-permissive LIKE filters are
> > arguably the more dangerous symptom for applications.
> >
>
> I have updated the commit message. I also added another test for this
> scenario in v3.
>
> > 2. A small typo in the new comment in like_match.c:
> > "occurences" should be "occurrences".
> >
>
> Fixed the typo.
>
> Thanks,
> Nitin Motiani
> Google