HHVM no longer part of WordPress core’s testing infrastructure

WordPress has never officially supported HHVM, but since WordPress 4.0 it has been compatible, largely thanks to the efforts of @wonderboymusic in #27881 and other tickets.

Many large scale sites which switched to HHVM around 2014 have since switched to PHP 7, and usage numbers of HHVM according to the wordpress.org update statistics indicate that HHVM powers only several dozen WordPress websites as of April 2017.

Core’s unit test suite when run on HHVM never actually passed (this may not be completely accurate, memories are hazy), often errored completely, and was always marked as an allowed failure. All of this, coupled with the disproportionately high amount of effort required to maintain the test and CI infrastructure for HHVM, means that WordPress core is no longer tested on HHVM as part of the Travis CI build. See #40548 for details.

If you’re running a WordPress website on HHVM, you should consider switching to PHP 7+ which is far more widely supported and tested, and offers all of the memory and performance benefits that HHVM pushed forward.