I have an account on TheTestWiki.org. On that wiki, there is a "test" user group that allows admins to test adding and removing rights through Special:UserRights. However, when I tried to add the "test" group to my account on that wiki, I kept getting an error message that said "the expiry time for group "sysop" is invalid". My account has indefinite sysop rights on that wiki, and I didn't touch the sysop right when attempting to add the test group. This is weird, and the owner of the wiki says that it's a MediaWiki issue. See the screenshot below.
Customize query in gerrit
|mediawiki/core||master||+4 -0||Fix issue when modifying groups in Special:Userrights|
Confirmed with the following configuration settings on MediaWiki-Vagrant:
$wgGroupPermissions['test']['read'] = true; $wgGroupsAddToSelf['sysop'] = 'test'; $wgGroupsRemoveFromSelf['sysop'] = true;
Adding the third line seems to do the trick. If it is disabled, adding and removing rights functions fine.