Unsetting undefined variable is not an issue

[jrfnl]

Trying to unset an undefined variable is not an issue in PHP and will not result in any warnings/notices: https://3v4l.org/XsK20

The following code snippet:

function foo($array) {
	foreach ($array as $value) {
	}
	unset($key, $value);
}

... currently results in the following warning for using $key in unset():

----------------------------------------------------------------------
FOUND 0 ERRORS AND 1 WARNING AFFECTING 1 LINE
----------------------------------------------------------------------
 6 | WARNING | Variable $key is undefined.
----------------------------------------------------------------------

I'd like to propose to either not throw an error for undefined variables being used in unset() or to give this a separate error code so those kind of warnings can be silenced.

[sirbrillig]

Trying to unset an undefined variable is not an issue in PHP

That's good to know, but I wonder if it might still be a sign that there's a typo. For example:

function foo($array) {
  unset($ary['value']);
  return $array;
}

In that case, I'd want to be warned that I'm using a variable that's undefined. Is there a real use-case where this would be problematic?

That said, I'd be happy to split this case into its own sniff code if it would help someone.

[jrfnl]

In that case, I'd want to be warned that I'm using a variable that's undefined.

Good point.

I'd be happy to split this case into its own sniff code if it would help someone.

👍

Is there a real use-case where this would be problematic?

Yes, I can think of a case where a variable would be conditionally unset, with an isset() later on to determine whether to continue or not. A typo in that case would break the logic.

Fake, nonsense code to demonstrate:

function foo() {
    $a = null;
    $b = null;
    $array = function_call();
    list($a, $b) = $array;
    if ($a < 20) {
        unset($aa); // Typo
    }
    if ($b < 20) {
        unset($b);
    }

    if (isset($a, $b) === false) {
        return;
    }

    // Do something.