Bug report

array_keys would never return a key that is not already part of the (narrowed) key type.

a simple first fix (i suppose): just removing this check: https://github.com/phpstan/phpstan-src/blob/612ee600d58315b23506a8a148b0100597b7661b/src/Type/Php/ArrayKeysFunctionDynamicReturnTypeExtension.php#L30

While this might not fix all cases, it would certainly fix the cases of narrowed array-key types to int or string? (*)

(*) with the known caveat of the internal type conversion of integer strings, of course

Code snippet that reproduces the problem

https://phpstan.org/r/f43ddd65-69db-4d3e-acb4-9d2689e5f5b3

Expected output

8: Dumped type: list<int>
11: Dumped type: list<int>

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