pub struct S(i32);

mod a {
    pub fn call_foo(s: &super::S) { s.foo(); }

    mod b {
        fn some_method_private_to_b() {
            println!("inside some_method_private_to_b");
        }

        impl super::super::S {
            pub(a) fn foo(&self) {
                some_method_private_to_b();
                println!("only callable within `a`: {}", self.0);
            }
        }
    }
}

fn main() { }