No way to annotate array key template

[muglug]

Bug report

/**
 * @template T as int|string
 *
 * @param array<T, mixed> $arr
 * @return array<int, T>
 */
function my_array_keys($arr) {
	return array_keys($arr);
}

$a = my_array_keys(["hello" => 5, "goodbye" => new \Exception()]);

https://phpstan.org/r/b92e2661-21cd-4182-b987-312171de77fd

Expected output

No issues

Actual

Function my_array_keys() should return array<int, T> but returns array<int, (int|string)>.

[ondrejmirtes]

The weirdest thing here is tha @template T as int|string isn't reported as unsupported, which it should be: https://phpstan.org/r/c4869d53-2241-455f-a705-5ab447090799

[ondrejmirtes]

It's because of as instead of of: https://phpstan.org/r/6b4f0a22-a01d-435a-9875-2e786cbe6b7c

Error without bound: https://phpstan.org/r/bf701ed3-fcc5-481d-acb6-8c86db431039

[github-actions]

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