Casting down iterable in else branch sometimes doesn't preserve type params

[bugreportuser]

#1997 fixed most issues. However, Psalm still has trouble inferring the types for this function.

Removing T1 fixes the issue.

Example (https://psalm.dev/r/aa78059e8a):

<?php
/**
 * @template T1 as array-key
 * @template T2
 *
 * @param iterable<T1,T2> $x
 *
 * @return array<T1,T2>
 */
function iterableToArray (iterable $x): array {
    if (is_array($x)) {
        return $x;
    }
    else {
        return iterator_to_array($x);
    }
}

/** @var iterable<int,int> */
$x = null;
iterableToArray($x);

Example output:

ERROR: InvalidReturnStatement - 15:16 - The type 'array<array-key, mixed>' does not match the declared return type 'array<T1 as array-key, T2 as mixed>' for iterableToArray

ERROR: InvalidReturnType - 8:12 - The declared return type 'array<T1, T2>' for iterableToArray is incorrect, got 'array<T1|array-key, T2|mixed>'

[bugreportuser]

Thanks!

[paxal]

Hi ! I'm still having this kind of issue despite being on v3.6.4 : result is marked as array, and calling sleep(iterableToArray($x)) raises a MixedArgument issue :
https://psalm.dev/r/cc8c7ed010

[muglug]

@paxal mind ticketing that separately?