The variable is also read in a few other places, such as to
export the value from api.php (siteinfo) and load.php (mw.config)
but those requests don't need to be held back by this extra
logic.
Alternatively, if we really want to require this for all consumption,
we should probably let PathRouter provide the value and require
consumers to use it. E.g. services->getPathRouter->getArticlePath,
or something like that.
As easy first step, I'm moving it to PathRouter, called from
WebRequest::getPathInfo which is still called on all index.php
requests for any wiki page action in any namespace (incl Special)
when the wiki uses anything other than the default 'index.php?title='
article path.
Test Plan:
* Set '$wgArticlePath = 'bla';`
* View /mediawiki/index.php/Main_Page, and observe the fatal
error message (same as before this change).
Bug: T189966
Change-Id: Id06c2557e2addb58faeef0b6f7767a65b8de55a5
