Description:
------------
A memory leak occurs when a closure that is defined inside a class and has a parameter named $this is invoked with a value that contains a reference to $this.

This gist (https://gist.github.com/jmalloc/e3db5842c2c4ab2a1edf) might help explain a little better.

Affected PHP versions: https://3v4l.org/lr963

Test script:
---------------
class MemoryLeak
{
    public function bad()
    {
        $closure = function ($this) {};
        $closure([$this]);
    }
}

$object = new MemoryLeak;
ini_set('memory_limit', '10M');

for ($i = 0; $i < 1000000; ++$i) {
    $object->bad();
}

echo "Done" . PHP_EOL;

Expected result:
----------------
Done

Actual result:
--------------
Fatal error: Allowed memory size of 10485760 bytes exhausted (tried to allocate 4096 bytes) in /Users/james/<snip>/leak.php on line 8