Difference between enum-string and class-string<UnitEnum>

[zonuexe]

All enums implicitly inherit from UnitEnum, so calling the $enumString::cases() static method is always legal, but Psalm does not seem to behave that way: https://psalm.dev/r/ea20c1515d

/**
 * @param enum-string $s
 */
function f(string $s): void {
    $cases = $s::cases();
    var_dump($cases);
}

/**
 * @param enum-string<UnitEnum> $s
 */
function g(string $s): void {
    $cases = $s::cases();
    var_dump($cases);
}

I noticed this problem while checking the behavioral differences between PHPStan and Psalm to write a tutorial on typing in PHP.

refs #7404, phpstan/phpstan#12529, phpstan/phpstan-src#3807

[psalm-github-bot]

I found these snippets:

https://psalm.dev/r/ea20c1515d

<?php

/**
 * @param enum-string $s
 */
function f(string $s): void {
    $cases = $s::cases();
    var_dump($cases);
}

/**
 * @param enum-string<UnitEnum> $s
 */
function g(string $s): void {
    $cases = $s::cases();
    var_dump($cases);
}

Psalm output (using commit 5847d08):

INFO: MixedMethodCall - 7:14 - Cannot call method on an unknown class

INFO: MixedAssignment - 7:5 - Unable to determine the type that $cases is being assigned to

ERROR: ForbiddenCode - 8:5 - Unsafe var_dump

ERROR: ForbiddenCode - 16:5 - Unsafe var_dump