When you visit history of a page and apply some filters (example), you will see just the filter menu and explanations of some markers.
There should be some placeholder explaining why there are no results.
- create a message in languages/i18n/en.json and documentation in languages/i18n/qqq.json (https://www.mediawiki.org/wiki/Localisation)
- override IndexPager::getEmptyBody in HistoryPager class to print the new message (https://www.mediawiki.org/wiki/Manual:Messages_API#Using_messages_in_PHP)
- update HistoryPager::getStartBody and HistoryPager::getEndBody, so that they produce no HTML when HistoryPager::getNumRows returns 0
- Visit https://en.wikipedia.beta.wmflabs.org/w/index.php?date-range-to=&tagfilter=sillyqa&title=Main_Page&action=history
- A message should inform you that no matching revisions were found.
- Click filter revisions and remove "sillyqa" from the input box
- Check that the message doesn't show and there are results