On Friday, 25 July 2025 at 23:20, Niels Dossche <dossche.ni...@gmail.com> wrote:
> Hi internals
>
> On PHP 8.5-dev, we ship with pcre2lib 10.45.
>
> This includes a new opt-in feature called "PCRE2_ALT_EXTENDED_CLASS".
> It enables the use of complex character set operations in accordance to
> UTS#18 (Unicode Technical Standard 18).
> This means it becomes possible to nest character sets, perform set operations
> on them, etc.
> One example of such a set operation is a set subtraction, e.g. the regex
> "[\ep{L}--[QW]]" means "Unicode letters other than Q and W".
> Or a more realistic example (inspired from [1]): the regex "[\p{Lu}--[0-9]]"
> matches all non-ASCII unicode numbers.
> You can also do ORs, ANDs, etc.
>
> The reason this is opt-in in pcre2lib, is because the interpretation of
> existing regexes may change.
> This standard is being adopted in other languages too, also opt-in, for
> example in JavaScript [1].
> To expose this functionality in PHP, we also have to make it opt-in via a
> modifier.
>
> In JavaScript, this is enabled via the /v modifier at the end of the regex
> [1].
> This does the same thing as the /u modifier, but extends it with this UTS#18
> standard.
> We also already have /u in PHP that enables UTF-8 unicode mode. So we could
> do the same as JavaScript and add a /v modifier that extends /u and also
> enables PCRE2_ALT_EXTENDED_CLASS. Technically, you don't need unicode
> processing for enabling PCRE2_ALT_EXTENDED_CLASS, but as it comes from a
> unicode standard (and that at least JavaScript does this too), it may make
> sense to enable them both.
>
> The actual patch is trivial:
> `diff diff --git a/ext/pcre/php_pcre.c b/ext/pcre/php_pcre.c index
> 8e0fb2cce5f..4a4727545ad 100644 --- a/ext/pcre/php_pcre.c +++
> b/ext/pcre/php_pcre.c @@ -718,6 +718,9 @@ PHPAPI pcre_cache_entry*
> pcre_get_compiled_regex_cache_ex(zend_string *regex, bo case 'S': /* Pass. */
> break; case 'X': /* Pass. */ break; case 'U': coptions |= PCRE2_UNGREEDY;
> break; +#ifdef PCRE2_ALT_EXTENDED_CLASS + case 'v': coptions |=
> PCRE2_ALT_EXTENDED_CLASS; ZEND_FALLTHROUGH; +#endif case 'u': coptions |=
> PCRE2_UTF; /* In PCRE, by default, \\d, \\D, \\s, \\S, \\w, and \\W recognize
> only ASCII characters, even in UTF-8 mode. However, this can be changed by
> setting`
>
> What do we think?
>
> [1] https://github.com/tc39/proposal-regexp-v-flag
>
> Kind regards
> Niels
I'm in favour of this, as this is small and self-contained, I don't think this
should require an RFC.
Best regards,
Gina P. Banyard
