Background

Generic function bar calls generic function foo. Their templates (T and Q, respectively) have different names but the exact same definition.

A parameter of type value-of<Q> is passed unchanged to foo as a parameter of type value-of<T>.

Problem

PHPStan (both v1.12.7 and whatever version currently runs in the playground) deems the parameter type unsolvable.

This also happens if the templates are both named T (because, of course, they still are different templates).

Example code

<?php declare(strict_types = 1);

class Bug
{
    /**
     * @template T of BackedEnum
     * @param class-string<T> $class
     * @param value-of<T> $value
     */
    public static function foo(string $class, mixed $value): void
    {
    }

    /**
     * @template Q of BackedEnum
     * @param class-string<Q> $class
     * @param value-of<Q> $value
     */
    public static function bar(string $class, mixed $value): void
    {
        // Parameter #2 $value of static method Bug::foo() contains unresolvable type.
        self::foo($class, $value);
    }
}

Playground links

Same code as above: https://phpstan.org/r/b8dd4d29-d647-4d2e-bff5-cc6cddf4d9af

With both templates named T (same error): https://phpstan.org/r/32dce00f-6cec-486c-8479-25a2ac2b7c46

With template T unrestricted and Q of BackedEnum (same error): https://phpstan.org/r/83fcca8c-8c3d-448e-810d-d73ed3faecd9

With both templates unrestricted (no errors, but unfeasible for my use case): https://phpstan.org/r/1b4fe7c2-7516-4e98-8938-3d98908ef414

Expected output

No errors. PHPStan should be able to infer that a value-of<Q> is a value-of<T> if Q is equal to, or a subtype of, T.

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