impure.eval

Code example

<?php declare(strict_types = 1);

/**
 * @phpstan-pure
 */
function computeValue(string $code): mixed
{
	return eval($code); // ERROR: Impure eval in pure function computeValue().
}

Why is it reported?

A function or method marked as @phpstan-pure must not have side effects and must always return the same result for the same inputs. Using eval() inside a pure function is considered an impure operation because eval() can execute arbitrary code with unpredictable side effects -- it can modify global state, output content, define new functions or classes, and generally do anything that PHP code can do.

How to fix it

Remove the eval() call from the pure function, or remove the @phpstan-pure annotation if the function genuinely needs to use eval():

 <?php declare(strict_types = 1);

-/**
- * @phpstan-pure
- */
-function computeValue(string $code): mixed
+function computeValue(string $code): mixed
 {
 	return eval($code);
 }

Alternatively, refactor the function to avoid eval() entirely:

 <?php declare(strict_types = 1);

 /**
  * @phpstan-pure
  */
-function computeValue(string $code): mixed
+function computeValue(string $expression): int
 {
-	return eval($code);
+	return (int) $expression;
 }