Description:
------------
I'm getting incorrect results from preg_replace_callback() on PHP 7.3.0 when it fulfills the following conditions:

 - preg_replace_callback's input must contain at least 2 matches.
 - preg_replace_callback's callback must call filter_var() with FILTER_VALIDATE_REGEXP and filter_var's regexp must match its input.

From what I can tell, preg_replace_callback() keeps looping through matches internally (it requires at least 2 matches to trigger) and keeps doing replacements until it reaches its match limit or runs out of resources.

I wasn't able to reproduce this behaviour on a secondary machine, so there may be a platform-specific component to it. No issue on PHP 7.2.x


--------------------

PHP 7.3.0 (cli) (built: Dec 13 2018 08:57:16) ( NTS )
Copyright (c) 1997-2018 The PHP Group
Zend Engine v3.3.0-dev, Copyright (c) 1998-2018 Zend Technologies

Configure Command =>  './configure'  '--prefix=/usr' '--build=x86_64-pc-linux-gnu' '--host=x86_64-pc-linux-gnu' '--mandir=/usr/share/man' '--infodir=/usr/share/info' '--datadir=/usr/share' '--sysconfdir=/etc' '--localstatedir=/var/lib' '--docdir=/usr/share/doc/php-7.3.0' '--htmldir=/usr/share/doc/php-7.3.0/html' '--prefix=/usr/lib64/php7.3' '--mandir=/usr/lib64/php7.3/man' '--infodir=/usr/lib64/php7.3/info' '--libdir=/usr/lib64/php7.3/lib' '--with-libdir=lib64' '--localstatedir=/var' '--without-pear' '--disable-maintainer-zts' '--with-password-argon2=/usr' '--disable-bcmath' '--without-bz2' '--disable-calendar' '--disable-gcov' '--enable-ctype' '--with-curl=/usr' '--enable-dom' '--without-enchant' '--disable-exif' '--enable-fileinfo' '--enable-filter' '--disable-ftp' '--without-gettext' '--without-gmp' '--enable-hash' '--without-mhash' '--with-iconv' '--enable-intl' '--disable-ipv6' '--enable-json' '--without-kerberos' '--enable-libxml' '--with-libxml-dir=/usr' '--enable-mbstring' '--with-onig=/usr' '--with-openssl=/usr' '--with-openssl-dir=/usr' '--disable-pcntl' '--enable-phar' '--enable-pdo' '--enable-opcache' '--without-pgsql' '--disable-posix' '--without-pspell' '--without-recode' '--enable-simplexml' '--disable-shmop' '--without-snmp' '--disable-soap' '--disable-sockets' '--without-sodium' '--with-sqlite3=/usr' '--disable-sysvmsg' '--disable-sysvsem' '--disable-sysvshm' '--without-tidy' '--enable-tokenizer' '--disable-wddx' '--enable-xml' '--enable-xmlreader' '--enable-xmlwriter' '--with-xmlrpc' '--with-xsl=/usr' '--enable-zip' '--without-libzip' '--with-zlib=/usr' '--disable-debug' '--enable-dba' '--without-cdb' '--without-db4' '--disable-flatfile' '--without-gdbm' '--enable-inifile' '--without-qdbm' '--without-lmdb' '--without-freetype-dir' '--disable-gd-jis-conv' '--with-jpeg-dir=/usr' '--with-png-dir=/usr' '--without-xpm-dir' '--with-gd' '--without-interbase' '--with-mysqli=mysqlnd' '--with-mysql-sock=/var/run/mysqld/mysqld.sock' '--without-unixODBC' '--without-iodbc' '--without-oci8' '--without-pdo-dblib' '--with-pdo-mysql=mysqlnd' '--without-pdo-pgsql' '--with-pdo-sqlite=/usr' '--without-pdo-firebird' '--without-pdo-odbc' '--without-pdo-oci' '--with-readline=/usr' '--without-libedit' '--without-mm' '--with-pic' '--with-pcre-regex=/usr' '--with-pcre-dir=/usr' '--without-pcre-valgrind' '--without-pcre-jit' '--cache-file=/var/tmp/portage/dev-lang/php-7.3.0/temp/config.cache' '--with-config-file-path=/etc/php/cli-php7.3' '--with-config-file-scan-dir=/etc/php/cli-php7.3/ext-active' '--disable-embed' '--enable-cli' '--disable-cgi' '--disable-fpm' '--without-apxs2' '--disable-phpdbg' 'build_alias=x86_64-pc-linux-gnu' 'host_alias=x86_64-pc-linux-gnu' 'CPPFLAGS='

PCRE Library Version => 10.32 2018-09-10
PCRE Unicode Version => 11.0.0
PCRE JIT Support => not compiled in
pcre.backtrack_limit => 1000000 => 1000000
pcre.recursion_limit => 100000 => 100000


Test script:
---------------
<?php

function cb()
{
	filter_var('', FILTER_VALIDATE_REGEXP, ['options' => ['regexp' => '//']]);
	return '.';
}
var_dump(preg_replace_callback('/./', 'cb', 'xx', 10));


Expected result:
----------------
string(2) ".."



Actual result:
--------------
string(12) "..........xx"