[Downgrade PHP 7.3] list() and array destructuring reference assignment

[leoloso]

Feature Request

Downgrade new feature from PHP 7.3 to its equivalent PHP 7.2 code. RFC with explanation

This feature must be handled with care. Check in the RFC all the nuances, and if there is any instance where downgrading is not possible, identify that case in the rule and throw a DowngradeNotPossibleException.

Diff

$array = [1, 2];
-list($a, &$b) = $array;
+$a = $array[0];
+$b =& $array[1];

/* Note; []= syntax works the same, so the following is functionally equivalent to the example */
-[$a, &$b] = $array;
+$a = $array[0];
+$b =& $array[1];

[leoloso]

The solution involves 2 steps:

1. Remove the references from list
2. Add new nodes to override those assignments, doing it by reference with the supported =& operator

$array = [1, 2];
-list($a, &$b) = $array;
+list($a, $b) = $array;
+$b =& $array[1];