php/php-src — pull request #512 by nikita2206 (2013-10-29 15:43:42+00:00)
Title: date_diff() bug #65768

Fixed the bug when DateTimeInterface::diff() (and date_diff()) was declared as diff(DateTimeInterface, DateTimeInterface), but the implementations were always diff(DateTime, DateTime), even when working with DateTimeImmutable (which gave you a fatal in any case)

Here's a link to bugtracker https://bugs.php.net/bug.php?id=65768