With T183375, undeletion no longer sets the parent ids for the undeleted revisions to the "expected" one given by the previous revision by id (usually, but not always, also the previous revision by timestamp), but instead to the ar_parent_id values. For example, look at the [[https://en.wikipedia.org/w/index.php?title=Ernest_Madu&action=history|history of Ernest Madu on Wikipedia]], and you'll see that [[https://en.wikipedia.org/w/index.php?title=Ernest_Madu&oldid=820864133|revision 820864133]] has parent id 0 (with an "N" mark in the [[https://en.wikipedia.org/wiki/Special:Contributions/Andrewkazimi|user's contribs]]) instead of [[https://en.wikipedia.org/w/index.php?title=Ernest_Madu&oldid=820863993|820863993]]. While T183375 may have been a good idea, there are situations (such as selective undeletion or history splits) where it would be better to reset the parent ids like they had always been. We should therefore add a new checkbox (perhaps unchecked by default) in the Special:Undelete interface saying "Reset parent ids" or something similar to mimic the old behavior. If unchecked, ar_parent_id will be used as the rev_parent_id for the undeleted revisions, which is the current apparent behavior per T183375.