It seems when a user is loaded from session, but the UserLoadFromSession hook aborts the process (by settings $result to false), User::load() will just not do anything. In other words, when a hook aborts, the User private variables are not initialized, meaning $mId and $mName are still null rather than false. Because of this, MediaWiki thinks the user is logged in and has a blank username, causing an exception to be thrown when the personal URLs are generated in SkinTemplate::loadPersonalUrls(). This occurred using Git master.

Steps to reproduce:

1. Add this function somewhere:

function wfBugTest( $user, &$result ) {

$result = false;
return true;

}

2. Add the function into the UserLoadFromSession hook.
3. Try to access the wiki.

Expected Result: User is logged out no matter what.
Actual Result: Exception is thrown (details below).

MediaWiki internal error.

Original exception: exception 'MWException' with message 'SkinTemplate::makeTalkUrlDetails given invalid pagename User:' in /var/www/site/wiki/includes/SkinTemplate.php:727
Stack trace:
#0 /var/www/site/wiki/includes/SkinTemplate.php(654): SkinTemplate->makeTalkUrlDetails('User:')
#1 /var/www/site/wiki/includes/SkinTemplate.php(455): SkinTemplate->buildPersonalUrls()
#2 /var/www/site/wiki/includes/OutputPage.php(1998): SkinTemplate->outputPage()
#3 /var/www/site/wiki/includes/Wiki.php(543): OutputPage->output()
#4 /var/www/site/wiki/includes/Wiki.php(446): MediaWiki->main()
#5 /var/www/site/wiki/index.php(58): MediaWiki->run()
#6 {main}

Exception caught inside exception handler: exception 'MWException' with message 'SkinTemplate::makeTalkUrlDetails given invalid pagename User:' in /var/www/site/wiki/includes/SkinTemplate.php:727
Stack trace:
#0 /var/www/site/wiki/includes/SkinTemplate.php(654): SkinTemplate->makeTalkUrlDetails('User:')
#1 /var/www/site/wiki/includes/SkinTemplate.php(455): SkinTemplate->buildPersonalUrls()
#2 /var/www/site/wiki/includes/OutputPage.php(1998): SkinTemplate->outputPage()
#3 /var/www/site/wiki/includes/Exception.php(227): OutputPage->output()
#4 /var/www/site/wiki/includes/Exception.php(273): MWException->reportHTML()
#5 /var/www/site/wiki/includes/Exception.php(624): MWException->report()
#6 /var/www/site/wiki/includes/Exception.php(705): MWExceptionHandler::report(Object(MWException))
#7 /var/www/site/wiki/includes/Wiki.php(449): MWExceptionHandler::handle(Object(MWException))
#8 /var/www/site/wiki/index.php(58): MediaWiki->run()
#9 {main}

Version: unspecified
Severity: normal