Symptoms
========
With 1.29.0-wmf.9:
Warning: Empty regular expression in /srv/mediawiki/php-1.29.0-wmf.9/includes/parser/DateFormatter.php on line 200
Example of spam after wmf.9 deployments:
* 2017-01-25 20:50 rebuilt wikiversions.php and synchronized wikiversions files: group1 wikis to 1.29.0-wmf.9
{F5376790 size=full}
* 2017-01-26 13:01 rebuilt wikiversions.php and synchronized wikiversions files: group1 back to 1.29.0-wmf.9 T156310
{F5376770 size=full}
In both cases one can see a huge spike after 300?? seconds. And it is vanishing entirely after exactly(?) an hour.
Code
====
```
lang=php, name=includes/parser/DateFormatter.php
184 $regex = $this->regexes[$i];
185
186 // Horrible hack
187 if ( !$linked ) {
188 $regex = str_replace( [ '\[\[', '\]\]' ], '', $regex );
189 }
190
191 if ( $match_whole ) {
192 // Let's hope this works
193 $regex = preg_replace( '!^/!', '/^', $regex );
194 $regex = str_replace( $this->regexTrail,
195 '$' . $this->regexTrail, $regex );
196 }
197
198 // Another horrible hack
199 $this->mLinked = $linked;
200 $text = preg_replace_callback( $regex, [ &$this, 'replace' ], $text );
201 unset( $this->mLinked );
```
Note the nice comment hoping that will work.