I found that when extensions (example: MultimediaViewer, Popups[WIP]) want to add new option inside $wgDefaultUserOptions they do that via ExtensionFunctions.
This usually works but on Vagrant setup from time to time $wgDefaultUserOptions does not have all options registered - it might cause Special:Preferences page to break (for new users when they didn't save preferences yet).
Reason:
CookieSessionProvider on line 119 calls UserInfo::newFromId() that tries to fetch user data. Sometimes when data is not cached it will try to build data calling User::loadOptions() and store user options in cache. Everything happens before calling ExtensionFunctions and because of that even extensions register new options in wgDefaultUserOptions those won't be visible for logged in user.
Stacktrace (call executed before calling ExtensionFunctions - one that prepopulates $user->getOptions()):
#0 User::getDefaultOptions() called at [/vagrant/mediawiki/includes/user/User.php:5138]
#1 User->loadOptions() called at [/vagrant/mediawiki/includes/user/User.php:482]
#2 User->{closure}(, 3600, Array ([lag] => 0,[since] => 1481771446.3097,[pending] => ), ) called at [/vagrant/mediawiki/includes/libs/objectcache/WANObjectCache.php:880]
#3 WANObjectCache->{closure}(, 3600, Array ([lag] => 0,[since] => 1481771446.3097,[pending] => ), )
#4 call_user_func_array(Closure Object (), Array ([0] => ,[1] => 3600,[2] => Array ([lag] => 0,[since] => 1481771446.3097,[pending] => ),[3] => )) called at [/vagrant/mediawiki/includes/libs/objectcache/WANObjectCache.php:997]
#5 WANObjectCache->doGetWithSetCallback(global:user:id:wiki:9, 3600, Closure Object (), Array ([pcTTL] => 30,[version] => 10), ) called at [/vagrant/mediawiki/includes/libs/objectcache/WANObjectCache.php:886]
#6 WANObjectCache->getWithSetCallback(global:user:id:wiki:9, 3600, Closure Object (), Array ([pcTTL] => 30,[version] => 10)) called at [/vagrant/mediawiki/includes/user/User.php:495]
#7 User->loadFromCache() called at [/vagrant/mediawiki/includes/user/User.php:436]
#8 User->loadFromId(0) called at [/vagrant/mediawiki/includes/user/User.php:400]
#9 User->load() called at [/vagrant/mediawiki/includes/session/UserInfo.php:88]
#10 MediaWiki\Session\UserInfo::newFromId(9) called at [/vagrant/mediawiki/includes/session/CookieSessionProvider.php:119]
#11 MediaWiki\Session\CookieSessionProvider->provideSessionInfo(WebRequest Object ([] => Array ([title] => Special:Preferences),[] => Array ([HOST] => php5.local.wmftest.net:8080,[CONNECTION] => keep-alive,[CACHE-CONTROL] => max-age=0,[UPGRADE-INSECURE-REQUESTS] => 1,[USER-AGENT] => Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.75 Safari/537.36,[ACCEPT] => text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8,[DNT] => 1,[REFERER] => http://php5.local.wmftest.net:8080/wiki/Special:CreateAccount,[ACCEPT-ENCODING] => gzip, deflate, sdch,[ACCEPT-LANGUAGE] => pl,en-US;q=0.8,en;q=0.6,[COOKIE] => wikimwuser-sessionId=24f60d8595841f3e; optin=beta; mf_testcookie=test_value; stopMobileRedirect=true; XDEBUG_SESSION=PHPSTORM; wiki_session=hc1favqr43n52jg6uhjci40uns4up96r; wikiUserID=9; wikiUserName=Test5),[] => ,[] => 10.0.2.2,[] => 1481771446.221,[] => ,[] => ,[] => )) called at [/vagrant/mediawiki/includes/session/SessionManager.php:486]
#12 MediaWiki\Session\SessionManager->getSessionInfoForRequest(WebRequest Object ([] => Array ([title] => Special:Preferences),[] => Array ([HOST] => php5.local.wmftest.net:8080,[CONNECTION] => keep-alive,[CACHE-CONTROL] => max-age=0,[UPGRADE-INSECURE-REQUESTS] => 1,[USER-AGENT] => Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.75 Safari/537.36,[ACCEPT] => text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8,[DNT] => 1,[REFERER] => http://php5.local.wmftest.net:8080/wiki/Special:CreateAccount,[ACCEPT-ENCODING] => gzip, deflate, sdch,[ACCEPT-LANGUAGE] => pl,en-US;q=0.8,en;q=0.6,[COOKIE] => wikimwuser-sessionId=24f60d8595841f3e; optin=beta; mf_testcookie=test_value; stopMobileRedirect=true; XDEBUG_SESSION=PHPSTORM; wiki_session=hc1favqr43n52jg6uhjci40uns4up96r; wikiUserID=9; wikiUserName=Test5),[] => ,[] => 10.0.2.2,[] => 1481771446.221,[] => ,[] => ,[] => )) called at [/vagrant/mediawiki/includes/session/SessionManager.php:189]
#13 MediaWiki\Session\SessionManager->getSessionForRequest(WebRequest Object ([] => Array ([title] => Special:Preferences),[] => Array ([HOST] => php5.local.wmftest.net:8080,[CONNECTION] => keep-alive,[CACHE-CONTROL] => max-age=0,[UPGRADE-INSECURE-REQUESTS] => 1,[USER-AGENT] => Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/55.0.2883.75 Safari/537.36,[ACCEPT] => text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8,[DNT] => 1,[REFERER] => http://php5.local.wmftest.net:8080/wiki/Special:CreateAccount,[ACCEPT-ENCODING] => gzip, deflate, sdch,[ACCEPT-LANGUAGE] => pl,en-US;q=0.8,en;q=0.6,[COOKIE] => wikimwuser-sessionId=24f60d8595841f3e; optin=beta; mf_testcookie=test_value; stopMobileRedirect=true; XDEBUG_SESSION=PHPSTORM; wiki_session=hc1favqr43n52jg6uhjci40uns4up96r; wikiUserID=9; wikiUserName=Test5),[] => ,[] => 10.0.2.2,[] => 1481771446.221,[] => ,[] => ,[] => )) called at [/vagrant/mediawiki/includes/WebRequest.php:735]
#14 WebRequest->getSession() called at [/vagrant/mediawiki/includes/session/SessionManager.php:128]
#15 MediaWiki\Session\SessionManager::getGlobalSession() called at [/vagrant/mediawiki/includes/Setup.php:759]
#16 require_once(/vagrant/mediawiki/includes/Setup.php) called at [/vagrant/mediawiki/includes/WebStart.php:137]
#17 require(/vagrant/mediawiki/includes/WebStart.php) called at [/vagrant/mediawiki/index.php:42]
#18 require(/vagrant/mediawiki/index.php) called at [/var/www/w/index.php:5]I experienced this issue when I was working on T146889. Everything works pretty well but when I'm spamming Special:Preferences page it breaks from time to time. As we want to store the default options in configuration I cannot use callback in extension.json because I cannot use ConfigFactory on that state.