Re: [PHP-DEV][PRE-RFC] PREG_THROW_ON_ERROR flag

On Tue, Jul 7, 2026 at 4:17 AM Osama Aldemeery <[email protected]> wrote:

> Hi all,
>
> I'd like to propose adding a `PREG_THROW_ON_ERROR` flag to the `preg_*()`
> functions, and gauge interest in that.
>
> Json and `ext/filter` both grew an opt-in way to turn a silent error into
> an exception...that is `JSON_THROW_ON_ERROR` and `FILTER_THROW_ON_FAILURE`.
> PCRE is the one left out where a failing call is easy to miss. An
> execution error for example (e.g. a bad UTF-8) surfaces only if
> you call `preg_last_error()` afterwards, and a malformed pattern emits a
> warning and returns `false`.
>
> `PREG_THROW_ON_ERROR` would do for PCRE what those two do for their
> functions.
> Passing it to any `preg_*()` call makes a PCRE error throw a
> `Pcre\PcreException` that carries the `PREG_*_ERROR` code and the
> `preg_last_error_msg()` text
> instead of warning or returning `false`/`null`.
> And it covers both kinds: a compilation error (e.g. a malformed pattern)
> and an execution error, so opting in means any PCRE failure becomes a
> single catchable exception.
> Also, `preg_replace()` and `preg_filter()` gain an optional `$flags`
> parameter to accept it (the only two without one as far as I know).
>
> Concretely, the check you'd write today:
>
> ```
> if (preg_match($pattern, $subject, $m) === false) {
>     throw new RuntimeException(preg_last_error_msg());
> }
> ```
>
> ...collapses to:
>
> ```
> preg_match($pattern, $subject, $m, PREG_THROW_ON_ERROR);
> ```
>
> First, I'd like to know whether there's interest at all and whether anyone
> sees a reason not to add it.
>
> If there is interest, a couple of design questions I'd want the list's
> read on:
>
>    1. Array subjcets. Currently `preg_last_error()` reflects only the
>    last element processed, but I'd have the flag throw on the first
>    failing element rather than keep last-one-wins...does that seem right?
>    2. Whether `*_ON_ERROR` reads better than `*_ON_FAILURE` given the
>    existing `preg_last_error()`/`PREG_*_ERROR` vocabulary.
>
> If it seems worth pursuing, I'll write it up as a proper RFC.
>
> Thanks,
> Osama
>

Hi all,

I've put together a complete implementation across all the `preg_*()`
functions so I can open a PR if it helps the discussion.

For now I've got it throwing on the first failing element for arrays, and
went with `PREG_THROW_ON_ERROR` for the flag name, just so I could complete
the implementation.
Still eager to hear what people have to say about that though, and to know
whether there's interest/objection before I take it further.

Thanks,
Osama