Description:
------------
return type are not well tested, it sometimes throw unexcepted errors while meet IS_INDIREcT or IS_REFERENCE

Test script:
---------------
<?php
$array = array(1, 2, 3);
debug_zval_dump($array);

var_dump(foo());

function &foo() :string {
    global $array;
    return $array[1];
}

Expected result:
----------------
no error

Actual result:
--------------
PHP Fatal error:  Uncaught TypeError: Return value of foo() must be of the type string, unknown returned in /tmp/1.php on line 10 in /tmp/1.php:10
Stack trace:
#0 /tmp/1.php(6): foo()
#1 {main}
  thrown in /tmp/1.php on line 10