impure.superglobal

Code example

<?php declare(strict_types = 1);

/** @phpstan-pure */
function getParam(string $key): ?string
{
	return $_GET[$key] ?? null;
}

Why is it reported?

A function marked as @phpstan-pure accesses a PHP superglobal variable ($_GET, $_POST, $_SESSION, $_SERVER, $_COOKIE, $_FILES, $_ENV, $_REQUEST, or $GLOBALS). Superglobal access is impure because it reads from global mutable state. Pure functions should only depend on their input parameters.

How to fix it

Pass the needed value as a parameter instead:

 <?php declare(strict_types = 1);

-/** @phpstan-pure */
-function getParam(string $key): ?string
+/** @phpstan-pure */
+function getParam(array $params, string $key): ?string
 {
-	return $_GET[$key] ?? null;
+	return $params[$key] ?? null;
 }

Or remove the @phpstan-pure annotation if the function needs to access superglobals.