CommentParser::computeId has a parameter, ThreadItem $threadItem, and it checks that the object is an instance of either HeadingItem or CommentItem. Later, it sometimes tries to call $threadItem->addWarning( 'Duplicate comment ID' );
However, the addWarning method is not part of the ThreadItem interface, and while CommentItem::addWarning is defined, HeadingItem::addWarning() is not
See beta logstash: https://logstash-beta.wmflabs.org/goto/b2d5d6dba1a2543e737a94ccd8df9c50
Impact so far: 2 errors