Error Identifier: staticMethod.impossibleType

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);

class TypeChecker
{
    /**
     * @phpstan-assert-if-true int $value
     */
    public static function isInt(mixed $value): bool
    {
        return is_int($value);
    }
}

function doFoo(string $value): void
{
    if (TypeChecker::isInt($value)) {
        // never reached - a string is never an int
    }
}

Why is it reported? #

The call to a static method that performs a type check will always evaluate to false because the type of the argument makes it impossible for the check to succeed. PHPStan understands type-checking methods through @phpstan-assert-if-true and @phpstan-assert-if-false PHPDoc tags, as well as methods configured as type-specifying extensions.

In this example, TypeChecker::isInt() asserts that the value is int, but the argument is always string, so the check can never return true.

How to fix it #

Pass the correct variable or value to the type check:

 <?php declare(strict_types = 1);
 
-function doFoo(string $value): void
+function doFoo(string|int $value): void
 {
     if (TypeChecker::isInt($value)) {
         // now this branch can be reached
     }
 }

Or remove the impossible check if it is not needed:

 <?php declare(strict_types = 1);
 
 function doFoo(string $value): void
 {
-    if (TypeChecker::isInt($value)) {
-        // never reached
-    }
+    // handle string directly
 }

How to ignore this error #

You can use the identifier staticMethod.impossibleType to ignore this error using a comment:

// @phpstan-ignore staticMethod.impossibleType
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: staticMethod.impossibleType

Rules that report this error #

PHPStan\Rules\Comparison\ImpossibleCheckTypeStaticMethodCallRule [1]

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