function.impossibleHaystackValue

Code example

<?php declare(strict_types = 1);

enum Foo
{
	case ONE;
	case TWO;
}

function doFoo(int $i): void
{
	// Foo::ONE can never be an int, but 1 and 2 can.
	if (in_array($i, [Foo::ONE, 1, 2], true)) {
		echo 'yes';
	}
}

Why is it reported?

The haystack passed to in_array(), array_search() or array_keys() is a constant array, so PHPStan knows every value it contains. When a value in that array can never be equal (==) or identical (===, when the strict flag is true) to the needle type, comparing against it is pointless — that element can never produce a match.

In the example above, the needle $i is an int, so it can never be identical to the enum case Foo::ONE. The Foo::ONE element in the haystack is dead: only 1 and 2 can ever match. This usually points to a wrong value in the array or an incorrect needle type.

Only values with a finite type (such as enum cases, true, false, null, or constant scalars) are reported, since only those are certain never to match. If no haystack value can ever match, the whole in_array() call is impossible and is reported by function.impossibleType instead.

This rule is only applied at rule level 4 and above, and is currently part of Bleeding Edge.

How to fix it

Remove the value that can never match:

-	if (in_array($i, [Foo::ONE, 1, 2], true)) {
+	if (in_array($i, [1, 2], true)) {
 		echo 'yes';
 	}

Or, if the extra value was intended to be matched, fix the needle type so it can actually contain that value:

-function doFoo(int $i): void
+function doFoo(int|Foo $i): void
 {
 	if (in_array($i, [Foo::ONE, 1, 2], true)) {
 		echo 'yes';
 	}
 }

On PHP versions without native union types (before PHP 8.0), express the union in PHPDoc instead. See PHPDoc Types:

+/**
+ * @param int|Foo $i
+ */
 function doFoo($i): void
 {
 	if (in_array($i, [Foo::ONE, 1, 2], true)) {
 		echo 'yes';
 	}
 }

By default the needle and haystack types include those from PHPDocs. If you don't want PHPStan to consider PHPDoc types as certain, set treatPhpDocTypesAsCertain to false.