Unbreak reverting 'degroup' action

This is something that hasn't been working since January 2009, when AF
didn't have arrays and all variables were computed non-lazily. In fact,
when reverting "degroup", we used to take old groups from edit vars, but
the variable may not have been computed for such edit. Plus, we treated
the var collection as an array instead of an AbuseFilterVariableHolder
object, and exploded user_groups since it was a string. With this patch
everything should start working as intended.

Change-Id: I76917b2e331291bd42daeef8d048507dc38048cb

includes/AbuseFilter.php

@@ -1577,6 +1577,9 @@ class AbuseFilter {
 				if ( !$wgUser->isAnon() ) {
 					// Remove all groups from the user.
 					$groups = $wgUser->getGroups();
+					// Make sure that the stored var dump contains user groups, since we may
+					// need them if reverting this degroup via Special:AbuseFilter/revert
+					$vars->setVar( 'user_groups', $groups );
 
 					foreach ( $groups as $group ) {
 						$wgUser->removeGroup( $group );

includes/Views/AbuseFilterViewRevert.php

@@ -269,8 +269,7 @@ class AbuseFilterViewRevert extends AbuseFilterView {
 				return true;
 			case 'degroup':
 				// Pull the user's groups from the vars.
-				$oldGroups = $result['vars']['USER_GROUPS'];
-				$oldGroups = explode( ',', $oldGroups );
+				$oldGroups = $result['vars']->getVar( 'user_groups' )->toNative();
 				$oldGroups = array_diff(
 					$oldGroups,
 					array_intersect( $oldGroups, User::getImplicitGroups() )