While trying to figure out bug T171711, I deleted the page https://din.wikipedia.org/wiki/MediaWiki:Mobile-frontend-placeholder . Then I tried to use the undelete function to restore it, and got:
[WXnbrwpAIDMAAGS5FskAAACK] 2017-07-27 12:25:20: Fatal exception of type "UnexpectedValueException"
This definitely doesn't look right.
2017-07-27 12:25:20 [WXnbrwpAIDMAAGS5FskAAACK] mw1181 dinwiki 1.30.0-wmf.10 exception ERROR: [WXnbrwpAIDMAAGS5FskAAACK] /w/index.php?title=K%C3%ABc%C3%ABweek:Undelete&action=submit UnexpectedValueException from line 170 of /srv/mediawiki/php-1.30.0-wmf.10/includes/user/UserGroupMembership.php: UserGroupMembership::insert() needs a positive user ID. Did you forget to add your User object to the database before calling addGroup()? {"exception_id":"WXnbrwpAIDMAAGS5FskAAACK","caught_by":"mwe_handler"}
[Exception UnexpectedValueException] (/srv/mediawiki/php-1.30.0-wmf.10/includes/user/UserGroupMembership.php:170) UserGroupMembership::insert() needs a positive user ID. Did you forget to add your User object to the database before calling addGroup()?
#0 /srv/mediawiki/php-1.30.0-wmf.10/includes/user/User.php(3441): UserGroupMembership->insert(boolean)
#1 /srv/mediawiki/php-1.30.0-wmf.10/extensions/Flow/includes/TalkpageManager.php(263): User->addGroup(string)
#2 /srv/mediawiki/php-1.30.0-wmf.10/extensions/Flow/container.php(1274): Flow\TalkpageManager->getTalkpageManager()
#3 /srv/mediawiki/php-1.30.0-wmf.10/vendor/pimple/pimple/src/Pimple/Container.php(113): Closure$#148(Flow\Container)
#4 /srv/mediawiki/php-1.30.0-wmf.10/extensions/Flow/includes/Container.php(48): Pimple\Container->offsetGet(string)
#5 /srv/mediawiki/php-1.30.0-wmf.10/extensions/Flow/Hooks.php(1652): Flow\Container::get(string)
#6 /srv/mediawiki/php-1.30.0-wmf.10/includes/Hooks.php(186): FlowHooks::onArticleUndelete(Title, boolean, string, integer, array)
#7 /srv/mediawiki/php-1.30.0-wmf.10/includes/page/PageArchive.php(766): Hooks::run(string, array)
#8 /srv/mediawiki/php-1.30.0-wmf.10/includes/page/PageArchive.php(444): PageArchive->undeleteRevisions(array, boolean, string)
#9 /srv/mediawiki/php-1.30.0-wmf.10/includes/specials/SpecialUndelete.php(1141): PageArchive->undelete(array, string, array, boolean, User)
#10 /srv/mediawiki/php-1.30.0-wmf.10/includes/specials/SpecialUndelete.php(201): SpecialUndelete->undelete()
#11 /srv/mediawiki/php-1.30.0-wmf.10/includes/specialpage/SpecialPage.php(522): SpecialUndelete->execute(NULL)
#12 /srv/mediawiki/php-1.30.0-wmf.10/includes/specialpage/SpecialPageFactory.php(578): SpecialPage->run(NULL)
#13 /srv/mediawiki/php-1.30.0-wmf.10/includes/MediaWiki.php(287): SpecialPageFactory::executePath(Title, RequestContext)
#14 /srv/mediawiki/php-1.30.0-wmf.10/includes/MediaWiki.php(867): MediaWiki->performRequest()
#15 /srv/mediawiki/php-1.30.0-wmf.10/includes/MediaWiki.php(523): MediaWiki->main()
#16 /srv/mediawiki/php-1.30.0-wmf.10/index.php(43): MediaWiki->run()
#17 /srv/mediawiki/w/index.php(3): include(string)
#18 {main}If the page was too old and created by Mediawiki default (or similar), it may be also related to T171315: Running update.php fails on old database which have edits by inexistent user "Mediawiki default"
Based on the backtrace, it looks like Flow's internal user account used to create Flow talk pages doesn't exist?
Mysteriously, this works now. I just undeleted the page and it worked fine. I also looked at the return value of getTalkpageManager() in eval.php and it returned user ID 213 called Flow talk page manager. Maybe your request was the very first that created the talk page manager user, and this is something that fails only once per wiki?
It looks like the system user, when created, has a user ID that is 0 or negative, but I can't reproduce that. I tried simulating this process by running $user = User::newSystemUser( 'Test system user', [ 'steal' => true ] ); $user->getGroups(); $user->addGroup( 'flow-bot' ); in eval.php both locally and on test2wiki, and I couldn't get it to fail.
What will happen next? because I am still unable to undelete on hiwikiversity. As I can see this is not a small problem.
@Jayprakash12345: As told before, please do not change the Priority field if you do not work on tasks.
This may be fixed by https://gerrit.wikimedia.org/r/413767 or https://gerrit.wikimedia.org/r/413768.