actor Foo {
    init(bar: Int) { ... }
    let bar: Int
    
    // error: Covariant 'Self' or 'Self?' can only appear as the type of a property, subscript or method result; did you mean 'Foo'?
    // fix-it: Replace 'Self' with 'Foo'
    func printFoo(foo: Self) {
        print(foo.bar)
    }
}

extension Foo: Equatable {
    // error: Covariant 'Self' or 'Self?' can only appear as the type of a property, subscript or method result; did you mean 'Foo'?
    // fix-it: Replace 'Self' with 'Foo'
    static func == (lhs: Self, rhs: Self) -> Bool {
        lhs.bar == rhs.bar
    }
}