Feedback-ID: i0fe9450f:Fastmail
Date: Fri, 23 May 2025 12:22:21 +0900
From: Michael Paquier <michael@paquier.xyz>
To: Laurenz Albe <laurenz.albe@cybertec.at>
Cc: pgsql-bugs@lists.postgresql.org
Subject: Re: SIMILAR TO expressions translate wildcards where they shouldn't
Message-ID: <aC_p7b5H6pLICU_e@paquier.xyz>
References: <16ab039d1af455652bdf4173402ddda145f2c73b.camel@cybertec.at>
 <aC_K7JPXF0AdPZqB@paquier.xyz>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha512;
	protocol="application/pgp-signature"; boundary="Kggbu6NDWznZSGhC"
Content-Disposition: inline
In-Reply-To: <aC_K7JPXF0AdPZqB@paquier.xyz>
Archived-At: 
 <https://www.postgresql.org/message-id/aC_p7b5H6pLICU_e%40paquier.xyz>
Precedence: bulk


--Kggbu6NDWznZSGhC
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Fri, May 23, 2025 at 10:10:04AM +0900, Michael Paquier wrote:
> Oh, good catch.  [_[:alpha:]] and [[:alpha:]_] both that this should
> match every string made of a-zA-Z and underscores, but this is failing
> to do the job for the latter.
>=20
> +           if (pchar !=3D '^' && charclass_start)
> +               charclass_start =3D false;
>=20
> I'm a bit puzzled by this part about '^', though, resetting the fact
> that we are in a squared bracket section with '^' treated as an
> exception.  Perhaps this deserves a comment?

Ah, I see.  This is just a way of saying that the caret ^ should still
be able to track the first character in the character class.

Anyway, I don't think that the tests in the patch are complete.  For
example, '[[^](]' is transformed into '^(?:[[^](])$' in the SIMILAR TO
conversion with the patch, and before the patch we get
'^(?:[[^](?:])$'.  Note the translation of the last parenthesis '(' to
"(?:" when inside the character class, but your patch does not
document that.  AFAIU, we should not convert the parenthesis '(' while
in a multi-level character class as the patch does, but we have no
tests for it and the patch does not document this part, either.

Could it be possible to split the single SIMILAR TO expression into
multiple smaller pieces for each character that should not be
converted while inside a character class?  This is hard to parse as
written in your proposal of patch.
--
Michael

--Kggbu6NDWznZSGhC
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----
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=eVkg
-----END PGP SIGNATURE-----

--Kggbu6NDWznZSGhC--