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Date: Thu, 2 Oct 2025 10:15:23 +0200
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Subject: Re: [PHP-DEV] [DISCUSSION] Validating regex pattern
To: Juliette Reinders Folmer <php-internals_nospam@adviesenzo.nl>
Cc: internals@lists.php.net
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From: alex.daubois+php@gmail.com (Alexandre Daubois)

Hi,

> Historically, PHP supported three regex engines (POSIX, PCRE, Oniguruma).=
 The POSIX engine was dropped in PHP 7.0 and there is a draft RFC to drop s=
upport for Oniguruma [1], however, that still means that at this time PHP s=
upports two different regex engines, which each have their own criteria for=
 when a regex is a valid pattern, and for Oniguruma supports a multitude of=
 regex dialects [2].

I wasn't aware of that. Thanks for the info!

> It also makes the `FILTER_VALIDATE_REGEX_PATTERN` flag highly ambiguous a=
s it is unclear against which engine/dialect the regex would be validated.

Indeed, the multi-engine "issue" makes it clear that it would be ambiguous.

> Maybe the error code flags returned via `preg_last_error()` [4] should be=
 made more specific to allow for detecting when a regex function failed due=
 to an error in the regex.
> Maybe the extensions should get a "throw on invalid regex" option, either=
 via an ini flag, a new function parameter or via an existing function like=
 `mb_regex_set_options()`.

I like the first solution, I like the second one even more. It would
be aligned with JSON_THROW_ON_ERROR.

> I'm not sure what the best solution is, but going with an illogical solut=
ion just to try and avoid the RFC process is not the way to go IMO.

The purpose isn't to avoid the RFC process, I'll write one if
necessary. I just want to gather opinions and deduct if it's necessary
:)

=E2=80=94 Alexandre Daubois