Manual:How to debug/with MediaWiki-Vagrant and PHPStorm

1. Install an XDebug browser extension, such as XDebug helper (Chrome, Firefox).
2. Start listening to XDebug connections in PHPStorm with the phone icon (see image in step 2 here)
3. Switch on the XDebug browser extension
4. In the PHPStorm configuration go to Languges & Frameworks > PHP > Servers
   1. Add a new server with name and host dev.wiki.local.wmftest.net, port 8080 (or whatever you configured; can be checked with vagrant config --get http_port)
   2. Check "Use path mappings"
   3. Below that, in the "Absolute path on the server" column set /vagrant in the row that corresponds to your vagrant directory, and /var/www to the row that corresponds to the srv/docroot subdirectory
5. You are ready to go; set some breakpoints (by clicking on the empty space on the border to the left of your code) and make a request (reload the page or make it send an AJAX request)

For command-line debugging, instead of steps 1 and 3 you can use the xdebug_on command (and then xdebug_off to disable).

For other IDEs, see MediaWiki-Vagrant/Advanced_usage#MediaWiki debugging using Xdebug and an IDE in your host.