Contravariant argument produces error with splat operator

[wimski]

Bug report

Using contravariance in combination with the splat/spread operator (... / argument overloading) results in an error.

Code snippet that reproduces the problem

This snippet contains two examples:

1. Passing on a single contravariant argument, which produces no errors.
2. Passing on multiple (overloaded) contravariant arguments, which produces an error.

https://phpstan.org/r/77c82dd8-795e-4baa-89bc-52da67790e30

Expected output

I expected contravariance to work with overloading without producing an error, because I don't see how that would make a difference. It's just one versus many, but simple contravariance nonetheless.

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[canvural]

The issue is that with PHP8 and named arguments $foo inside the useFoos method can be array<string, Foo> See here: https://3v4l.org/piICI

So that's why PHPStan resolves it to array<int|string, Foo> And when you pass that to a method that expects array<int, FooInterface>, it complains.

You can try to use array<array-key, FooInterface> instead maybe.