switch.alwaysTrue

Code example

<?php declare(strict_types = 1);

/** @param 1|2 $i */
function doFoo(int $i): void
{
	switch ($i) {
		case 1:
			break;
		case 2:
			break;
		case 3:
			break;
	}
}

Why is it reported?

The comparison between the switch subject and this case value is always true. Once the subject's possible values are fully covered by the cases above, PHPStan knows one of them will always match — so any case listed afterwards can never be reached.

In the example above $i is always 1 or 2, so by the time execution could fall through to case 3 the subject has already matched. The same happens after every member of an enum has been covered:

<?php declare(strict_types = 1);

enum Suit
{
	case Hearts;
	case Diamonds;
}

function doFoo(Suit $suit): void
{
	switch ($suit) {
		case Suit::Hearts:
			break;
		case Suit::Diamonds:
			break;
		case Suit::Hearts: // always true, unreachable
			break;
	}
}

A case that always matches is only reported when other cases follow it. The last case of a switch is allowed to be always-true, since nothing below it becomes unreachable.

How to fix it

Remove the unreachable cases that follow the exhaustive one:

 switch ($i) {
 	case 1:
 		break;
 	case 2:
 		break;
-	case 3:
-		break;
 }

If one of the earlier cases was meant to match a different value, correct it so the subject is no longer fully covered before reaching the later case.