A method-level `@template T` is replaced by its bound when the argument's `@implements` binding is forwarded through an abstract class with an extra, unforwarded class template

[klunejko]

Observed under v0.10.3

/**
 * @template T of PBase
 * @template U of PBase
 */
interface Q10BoxInterface {}

/**
 * @template TSelf of Q10eAbstract
 * @template T of PBase
 * @template U of PBase
 * @implements Q10BoxInterface<T,U>
 */
abstract class Q10eAbstract implements Q10BoxInterface {}

/** @extends Q10eAbstract<Q10eConcrete,PA,PB> */
final class Q10eConcrete extends Q10eAbstract {}

final class Q10dGenericCreateShape
{
    /**
     * @template T of PBase
     * @template U of PBase
     * @param Q10BoxInterface<T,U> $dto
     */
    public function __construct(protected readonly Q10BoxInterface $dto) {}
}

new Q10dGenericCreateShape(new Q10eConcrete());

Actual:

Q10dGenericCreateShape::__construct(): Argument $dto expects Q10BoxInterface<invariant PBase>, but Q10BoxInterface<PA> was given

The given type is resolved with a single type argument (<PA>, U dropped) and the method template falls back to its bound, checked invariantly. The trigger is the extra leading TSelf template on the abstract class: the same chain without it (variant f, @extends Q10fAbstract<PA,PB>) passes, a direct @implements Q10BoxInterface<PA,PB> on the argument's class (variant d) passes, and the chained argument against a non-templated @param Q10BoxInterface<PA,PB> (variant g) passes.

Expected: T = PA, U = PB inferred from the argument, as PHPStan resolves the @extends → @implements chain; the call is accepted.

[rcalicdan]

@klunejko This issue is happening because of Positional Index Shift of Template Parameters.. I will create a dedicated PR for this..