(In reply to comment #0)

so, in 1.22wmf8, there is a new collapsibleTabs.js (
https://bits.wikimedia.org/static-1.22wmf8/skins/vector/collapsibleTabs.js

It has been moved from the Vector extension with almost no changes, see gerrit change 55524 and gerrit change 56711. This part in particular was not changed (https://gerrit.wikimedia.org/r/#/c/56711/5/modules/jquery.collapsibleTabs.js vs https://gerrit.wikimedia.org/r/#/c/55524/13/skins/vector/collapsibleTabs.js).

So this either actually magically works, or has never worked. (I haven't tested right now.)

[Unlike bug 50196 this isn't critical, as as far as I can see it doesn't break stuff.]

i definitely experienced exceptions caused by this, but this was while chasing bug 50196, which turned out to be, as you noted, unrelated.

i do not have a good reproduction recipe to demonstrate those exceptions, but it is clearly a bug.

i agree that setting it to "critical" maybe was a bit panicky - again, at the time i thought this issue was the source of the 50196 behavior.

peace.

This currently doesn't cause any bad behavior as far as I can see ($settings will never be undefined, apparently), but it's obviously a bug.

There's also something else in this file:

XXX: 'data' is undefined here, should the 'data' from the outer scope have
a different name?
$( this ).detach().prependTo( target ).data( 'collapsibleTabsSettings', data );

It would be nice if someone spent some time trying to understand what all that code is doing.

Adjusting bug summary and metadata.

Change 96918 had a related patch set uploaded by Yamelnychuk:
Fix collapsibleTabs code cleanup: null != undefined & undefined variables passed to .data().

https://gerrit.wikimedia.org/r/96918

Change 96918 merged by jenkins-bot:
Fix collapsibleTabs code cleanup: null != undefined & undefined variables passed to .data().

https://gerrit.wikimedia.org/r/96918

Fixed by Yaroslav as a GCI task, should be all pretty now. kipod, I hope this makes you happy ;)