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Error Identifier: possiblyImpure.superglobal

Every error reported by PHPStan has an error identifier. Here’s a list of all error identifiers. In PHPStan Pro you can see the error identifier next to each error and filter errors by their identifiers.

Code example #

<?php declare(strict_types = 1);

/**
 * @phpstan-pure
 */
function getUserAgent(): string
{
	return $_SERVER['HTTP_USER_AGENT'] ?? 'unknown';
}

Why is it reported? #

The function or method is marked as @phpstan-pure but accesses a superglobal variable such as $_GET, $_POST, $_SERVER, $_SESSION, $_COOKIE, $_FILES, $_ENV, or $_REQUEST. Superglobals represent external mutable state that can change between calls, so reading from or writing to them is a side effect. Pure functions must always return the same result for the same inputs.

How to fix it #

Pass the needed value as a parameter instead of accessing the superglobal directly:

 /**
  * @phpstan-pure
  */
-function getUserAgent(): string
+function getUserAgent(string $userAgent): string
 {
-	return $_SERVER['HTTP_USER_AGENT'] ?? 'unknown';
+	return $userAgent;
 }

Alternatively, remove the @phpstan-pure annotation if the function intentionally relies on superglobal state.

How to ignore this error #

You can use the identifier possiblyImpure.superglobal to ignore this error using a comment:

// @phpstan-ignore possiblyImpure.superglobal
codeThatProducesTheError();

You can also use only the identifier key to ignore all errors of the same type in your configuration file in the ignoreErrors parameter:

parameters:
	ignoreErrors:
		-
			identifier: possiblyImpure.superglobal

Rules that report this error #

• PHPStan\Rules\Pure\PureFunctionRule [1]
• PHPStan\Rules\Pure\PureMethodRule [1]

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