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
