Re: SIMILAR TO expressions translate wildcards where they shouldn't

On Thu, May 22, 2025 at 11:18:44PM +0200, Laurenz Albe wrote:
> The underscore before the [:alpha:] is left alone, but the one after
> it gets translated to a period. Now the underscore is a wildcard
> that corresponds to the period in regular expressions, but characters
> in square brackets should lose their special meaning. The code in
> utils/adt/regexp.c doesn't expect that square brackets can be nested.
>
> The attached patch fixes the bug.

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.

+ if (pchar != '^' && charclass_start)
+ charclass_start = false;

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?
--
Michael