PHP reports a warning if a use statement for a non-namespaced class is used in a non-namespaced context.
$ git checkout c48f489ba6 [SNIP] $ php5 -l tests/phpunit/includes/libs/rdbms/database/DatabaseSQLTest.php PHP Warning: The use statement with non-compound name 'InvalidArgumentException' has no effect in tests/phpunit/includes/libs/rdbms/database/DatabaseSQLTest.php on line 3 No syntax errors detected in tests/phpunit/includes/libs/rdbms/database/DatabaseSQLTest.php $ echo $? 0
This warning is printed during the mediawiki-core-php55lint and mediawiki-phpunit-php55-jessie jobs, but doesn't cause either to fail. HHVM seems to not warn about it.