Error Identifier: possiblyImpure.die
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 handleError(string $message): string
{
if ($message !== '') {
die($message); // ERROR: Possibly impure die in pure function handleError().
}
return 'ok';
}
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 die (or exit) inside a pure function is considered an impure operation because it immediately terminates the script, which is the most extreme side effect possible – the function never returns a value at all.
When PHPStan cannot determine with certainty whether the die 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 #
Remove the die call from the pure function, or remove the @phpstan-pure annotation if the function genuinely needs to terminate the script:
<?php declare(strict_types = 1);
-/**
- * @phpstan-pure
- */
function handleError(string $message): string
{
if ($message !== '') {
die($message);
}
return 'ok';
}
Alternatively, restructure the function so that it remains pure and the caller handles the termination:
<?php declare(strict_types = 1);
/**
* @phpstan-pure
*/
-function handleError(string $message): string
+function handleError(string $message): string
{
- if ($message !== '') {
- die($message);
- }
-
- return 'ok';
+ return $message !== '' ? $message : 'ok';
}
How to ignore this error #
You can use the identifier possiblyImpure.die to ignore this error using a comment:
// @phpstan-ignore possiblyImpure.die
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.die