possiblyImpure.global

Code example

<?php declare(strict_types = 1);

/**
 * @phpstan-pure
 */
function getValue(bool $useGlobal): int
{
	if ($useGlobal) {
		global $counter;
		return $counter;
	}

	return 42;
}

Why is it reported?

This identifier is not reported in practice because the global keyword is always considered definitely impure, not just possibly impure. PHPStan reports impure.global instead.

A function or method marked as @phpstan-pure may use the global keyword. The global keyword accesses mutable global state, which is a side effect. Pure functions must not have side effects and must always return the same result for the same inputs.

When PHPStan cannot determine with certainty whether the global statement always executes (for example, because it is inside a conditional branch), it reports a "possibly impure" error rather than a definite impure one.

How to fix it

Pass the dependency as a parameter instead of accessing it via global:

 /**
  * @phpstan-pure
  */
-function getValue(bool $useGlobal): int
+function getValue(bool $useGlobal, int $counter = 42): int
 {
-	if ($useGlobal) {
-		global $counter;
-		return $counter;
-	}
-
-	return 42;
+	return $useGlobal ? $counter : 42;
 }

Or remove the @phpstan-pure annotation if the function genuinely needs to access global state:

-/**
- * @phpstan-pure
- */
 function getValue(bool $useGlobal): int
 {
 	if ($useGlobal) {
 		global $counter;
 		return $counter;
 	}

 	return 42;
 }