php5-symfony-debug 2.7.5+dfsg-1 (amd64 binary) in ubuntu xenial

 This extension publishes several functions to help building powerful
 debugging tools.
 .
 symfony_zval_info():
  * exposes zval_hash/refcounts, allowing e.g. efficient exploration of
    arbitrary structures in PHP,
  * does work with references, preventing memory copying.
 symfony_debug_backtrace() works like debug_backtrace(), except that it
 can fetch the full backtrace in case of fatal errors
 .
 Symfony is a PHP framework, a set of tools and a development methodology.