For reference, I disagree that this is a "shellpolicy" issue. Its more of a "may cause db inconsistency/totally break things" issue

If this is not a shellpolicy issue then the other option is to make the extension compatible with CentralAuth. You can't just have it disabled.

To clarify something. I only suspect that it might not play nicely, I don't have evidence. If I'm wrong, please ignore this bug.

If the codebase of CentralAuth can be fixed, then this is the right product/component in Bugzilla. If this ends up as UserMerge being removed from Wikivoyage, this should probably go to "Wikimedia > Site requests" instead.

Still needs further investigation if both work well together though, might influence fixing bug 39817?

'wmgUseUserMerge' => array(
'default' => false,
'wikivoyage' => true,
'eswikivoyage' => false,
'hewikivoyage' => false,
'plwikivoyage' => false,
'ptwikivoyaye' => false,
'rowikivoyage' => false,
'ukwikivoyage' => false,
),

This is bad...

Random example:

01:53, 18 November 2013 Wrh2 (talk | contribs) Deleted user: (WT-en) Koavf (2598)
01:53, 18 November 2013 Wrh2 (talk | contribs) User (WT-en) Koavf (2598) merged to Koavf (36077)

MariaDB [centralauth_p]> select * from localuser where lu_name="(WT-en) Koavf";
+--------------+---------------+-----------------------+--------------------+

+--------------+---------------+-----------------------+--------------------+

+--------------+---------------+-----------------------+--------------------+
1 row in set (0.00 sec)

MariaDB [centralauth_p]> select gu_id, gu_name from globaluser where gu_name="(WT-en) Koavf";
+----------+---------------+

+----------+---------------+

+----------+---------------+
1 row in set (0.00 sec)

MariaDB [enwikivoyage_p]> select lu_name from centralauth_f_p.localuser AS localuser LEFT JOIN enwikivoyage_p.user AS user ON lu_name=user_name WHERE lu_wiki="enwikivoyage" AND user_name IS NULL;
+-------------------------+

+-------------------------+

+-------------------------+
34 rows in set (3.23 sec)

https://en.wikivoyage.org/w/index.php?title=Special:Log/usermerge&offset=&limit=500&type=usermerge&user= shows more accounts merged than that...

I ran queries across all the other wikivoyage databases with UserMerge enabled, and only dewikivoyage had ghost accounts...

MariaDB [dewikivoyage_p]> select lu_name from centralauth_f_p.localuser AS localuser LEFT JOIN user ON lu_name=user_name WHERE lu_wiki="dewikivoyage" AND user_name IS NULL;
+------------------------+

+------------------------+

+------------------------+
9 rows in set (0.13 sec)

(In reply to Kunal Mehta (Legoktm) from comment #6)

<https://en.wikivoyage.org/w/index.php?title=Special:Log/
usermerge&offset=&limit=500&type=usermerge&user=> shows more accounts merged
than that...

I'm going to assume that these accounts were never global to begin with.

Created attachment 15639
Query results of localnames table vs enwikivoyage user table

101 entries in localnames that don't exist on enwikivoyage anymore, see attachment.

Attached:

Change 139331 had a related patch set uploaded by Legoktm:
Add hook handler for UserMerge's DeleteAccount

https://gerrit.wikimedia.org/r/139331

Change 139331 merged by jenkins-bot:
Add hook handler for UserMerge's DeleteAccount

https://gerrit.wikimedia.org/r/139331

CentralAuth+UserMerge should work better now. Bug 66535 tracks the cleaning up of Wikimedia's centralauth database.