https://test.wikidata.org/w/index.php?title=Q7&action=history
https://test.wikidata.org/w/index.php?title=Q194&action=history
See https://www.wikidata.org/wiki/MediaWiki_talk:Gadget-Merge.js#New_merge_API
It seems the first of the two edits was made (removing the data from the first item). but the second edit (adding the data to the second item) never went through.
Version: master
Severity: major
Whiteboard: u=dev c=backend p=8
Problem is that we don't undo our changes to the first item (merge from) if the second item (merge target) can't be saved. There's also a TODO about that in the code "//todo if the second result is not a success we should probably undo the first change".
Solving that in a clean manner is hard, I guess... but this is actually causing trouble in production.
Change 105666 had a related patch set uploaded by Addshore:
Undo any edits if a Merge Fails!
Change 105666 abandoned by Addshore:
Undo any edits if a Merge Fails!
Reason:
per comment
After further discussion with Hoo it turns out the failed merges are due to the database having bad data in it already, i.e. two items that have the same label and description.
Because of this we can not simply undo the edit as wikibase will not allow this edit to happen.
Instead we should check that both edits will be possible before merging, this might require some further refactoring of content handler classes
Change 110380 had a related patch set uploaded by Addshore:
Check for Label/Description conflicts in ChangeOpsMerge