Error Identifier: pureFunction.redundantUnlessCallable

← Back to pureFunction.*

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);

/**
 * @param pure-callable(int): int $f
 * @param array<int> $arr
 * @return array<int>
 * @pure-unless-callable-is-impure $f
 */
function myMap(callable $f, array $arr): array
{
	$result = [];
	foreach ($arr as $i => $v) {
		$result[$i] = $f($v);
	}

	return $result;
}

Why is it reported? #

The @pure-unless-callable-is-impure tag marks a function as pure except when the named callable parameter is impure — its purity depends on the callable passed in at each call site.

Here the parameter $f is typed as pure-callable, which guarantees it is always pure. Because the only condition that could make the function impure can never happen, the tag has no effect: the function is unconditionally pure. Marking it @pure-unless-callable-is-impure is misleading and hides the fact that the function can simply be declared @phpstan-pure.

How to fix it #

Replace @pure-unless-callable-is-impure with @phpstan-pure:

 /**
  * @param pure-callable(int): int $f
  * @param array<int> $arr
  * @return array<int>
- * @pure-unless-callable-is-impure $f
+ * @phpstan-pure
  */
 function myMap(callable $f, array $arr): array
 {
 	$result = [];
 	foreach ($arr as $i => $v) {
 		$result[$i] = $f($v);
 	}

 	return $result;
 }

If the function is actually meant to accept impure callables, widen the parameter type from pure-callable to callable so that the @pure-unless-callable-is-impure tag becomes meaningful again:

 /**
- * @param pure-callable(int): int $f
+ * @param callable(int): int $f
  * @param array<int> $arr
  * @return array<int>
  * @pure-unless-callable-is-impure $f
  */
 function myMap(callable $f, array $arr): array

How to ignore this error #

You can use the identifier pureFunction.redundantUnlessCallable to ignore this error using a comment:

// @phpstan-ignore pureFunction.redundantUnlessCallable
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: pureFunction.redundantUnlessCallable

Rules that report this error #

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