Change #1136416 had a related patch set uploaded (by Daniel Kinzler; author: Daniel Kinzler):

[mediawiki/core@master] undeletion: fix before-state in PageRevisionUpdatedEvent

https://gerrit.wikimedia.org/r/1136416

In T391739#10739989, @gerritbot wrote:

Change #1136416 had a related patch set uploaded (by Daniel Kinzler; author: Daniel Kinzler):

[mediawiki/core@master] undeletion: fix before-state in PageRevisionUpdatedEvent

https://gerrit.wikimedia.org/r/1136416

Note that this patch does not directly address the error as reported. The cause of the error is still unknown. It just fixes an inconsistency in related code, in the hope that it may avoid similar issues in the future. If we are lucky, it may end up fixing the error at hand as well.

I have not been able to preproduce the error locally. It would be useful to know whether it happens consistently for a given page, or if it just fails temporarily and later succeeds.

Actually... undeletion of https://en.wikipedia.org/wiki/City_University_of_Mogadishu failed on April 12, but the page was already undeleted on April 7th.

Was this a redundant undeletion attempt?

It happens consistently for the link in the task. https://en.wikipedia.org/wiki/Special:Undelete/City_University_of_Mogadishu

In T391739#10740141, @Pppery wrote:

It happens consistently for the link in the task. https://en.wikipedia.org/wiki/Special:Undelete/City_University_of_Mogadishu

Thanks. I don't have sysop rights on enwiki, so I couldn't test. My suspicion is that this happens when trying to undelete a page that has already been undeleted. I'll work on reproducing it some more.

@Pppery Are there still archived revisions for this page?

Yes, there's one deleted edit, which is a redirect. And the current version isn't a redirect.

Also note https://en.wikipedia.org/wiki/User_talk:Explicit#c-Explicit-20250407144800-Gene93k-20250407143600

In T391739#10740193, @Pppery wrote:

Yes, there's one deleted edit, which is a redirect. And the current version isn't a redirect.

Found it, thanks:

wikiadmin2023@10.64.32.13(enwiki)> select * from archive where ar_namespace = 0 and ar_title = "City_University_of_Mogadishu"\G
*************************** 1. row ***************************
        ar_id: 125386430
 ar_namespace: 0
     ar_title: City_University_of_Mogadishu
ar_comment_id: 502702150
     ar_actor: 196994261
 ar_timestamp: 20250325120203
ar_minor_edit: 1
    ar_rev_id: 1282270151
   ar_deleted: 0
       ar_len: 46
   ar_page_id: 59150008
 ar_parent_id: 1281929205
      ar_sha1: 8owcrlk025vks0s5q1drhuejrvnnovo
1 row in set (0.001 sec)

I see nothing special there... the fact that it's a redirect shouldn't matter...

The archived revision is newer than the newest revision on the page. So undeleting it would update the page content without creating the page. That's indeed the special case that I'm dealing with in the patch... though I couldn't trigger the error in my tests.

@Pppery Can you try making an edit to the page, so there is a newer version, and then undeleting the remaining revision? See if that works? It would just get injected into the history as the second-newest...

That worked.

In T391739#10740315, @Pppery wrote:

That worked.

Cool, thanks for checking! let's keep the ticket open anyway, until we are sure the cause is fixed. I'll summarize my findings later.

It's still not clear to me why and how this happens, but I have hopes for my patch to fix it. It's see what happens once it rides the train.

Change #1136416 merged by jenkins-bot:

[mediawiki/core@master] UndeletePage: fix before-state in PageRevisionUpdatedEvent

https://gerrit.wikimedia.org/r/1136416

The error ewas last seen on April 17. Seems like it's fixed.