Last modified: 2013-01-24 13:31:53 UTC
On e.g., http://www.mediawiki.org/w/index.php?title=Anti-spam_features&action=history we see plenty of "(undo)" links. Well some of them are fine, however others are 'boobytrapped', telling users "The edit could not be undone due to conflicting intermediate edits." So perhaps don't offer the boobytrapped ones, or label them something other than "undo"... if indeed it is computationally feasible.
My understanding of the undo process is that in order to determine whether an undo is possible, MediaWiki has to retrieve the full text of three revisions. If you're undoing one edit, that's acceptable. If you're viewing a history page containing 100 (or more) revisions and want to know whether each of them are undoable, that's not so good.
OK feel free to 'WONTFIX: too expensive'.
