@Lea_WMDE : I think we agreed in the daily that the hike wouldn't instantly pick this up and instead we'd maybe see if camp would be looking at it as an API bug. In that case I've de-tagged the hike.

@Tarrow @Jakob_WMDE @Pablo-WMDE @Matthias_Geisler_WMDE after talking to @thiemowmde: He also doesn't see a reason why the behavior should be kept this way, but suggests making a git bisect to understand since when the behavior exists and to see if this was maybe introduced as a fail save.

The documentation does not explicitly mention the current behavior, neither it would be implicitly concluded from that documentation. This is a bug that need to be fixed.

Though, it can be that some api users found out about it by coincidence and used it to achieve some shortcut implementation for some case they have.

Check the logs for such calls (where { ... aliases: { 'lang': [] } } ... } , i.e on a single language) to get a better feeling whether this might been used as a feature

In case you are referring to the documentation in docs/change-op-serializations.wiki, note I wrote this very late (in 2017), based on experiments and information I was able to extract directly from the code at this time. I simply missed the special case that ignores an empty list of aliases. Otherwise that special case would have become part of the documentation.

I still agree we should continue as if it is a bug. The fact it did not made it in any documentation is helpful now. ;-)

@thiemowmde that's great! let's hope no one have caught it and relied on it since then :)

I checked some logs (in hadoop, thanks @Ladsgroup for your help getting them).

Last month, the first 50 requests to wbeditentity that contained any empty array for some language in aliases did not seem like this "bug" has been used as a "feature" in them. The following example items were submitted with an empty array for aliases, but that was because they did have no aliases in the corresponding languages: https://www.wikidata.org/wiki/Q62003178, https://www.wikidata.org/wiki/Q7294838, https://www.wikidata.org/wiki/Q13634732, https://www.wikidata.org/wiki/Q13634732, https://www.wikidata.org/wiki/Q12681550, https://www.wikidata.org/wiki/Q62061893, https://www.wikidata.org/wiki/Q12681509, https://www.wikidata.org/wiki/Q1590383, https://www.wikidata.org/wiki/Q62016440.

As it is also not so obvious how this "bug" can be actually useful as a "feature" in the first place, I think we should just treat as a bug and go on fixing it without the need for any breaking change announcement. @Lydia_Pintscher @Lea_Lacroix_WMDE if that sounds sensible to you, I'll move it to ready to go on top today so that we take it in story time tomorrow.

Edit: after talking with Lea, we decided to go for a breaking change, just to be safe and make sure that we don't accidentally change the behaviour of editors' tools.

Breaking change process running:

• May 14th: announcement
• May 28th or earlier: bugfix deployed on beta
• June 17th: bugfix deployed on wikidata.org

Change 510204 had a related patch set uploaded (by Michael Große; owner: Michael Große):
[operations/mediawiki-config@master] Add feature flag config for breaking Wikibase API change

https://gerrit.wikimedia.org/r/510204

Change 510205 had a related patch set uploaded (by Michael Große; owner: Michael Große):
[mediawiki/extensions/Wikibase@master] Rename method to better reflect actual function

https://gerrit.wikimedia.org/r/510205

Change 510206 had a related patch set uploaded (by Michael Große; owner: Michael Große):
[mediawiki/extensions/Wikibase@master] Allow set aliases to empty with wbeditentity

https://gerrit.wikimedia.org/r/510206

Update: because Operations team have their offsite next week, the deployment on wikidata.org is postponed to June 17th.

The change is now deployed on wikidata.org!