pub mod a {
    pub trait Tr {
        fn f(&self);
    }
}

pub mod test1 {
    use super::a::Tr;

    pub struct S;

    impl Tr for S {
        fn f(&self) {
            println!("ok 1");
        }
    }
}

pub mod test2 {
    pub struct S;

    impl super::a::Tr for S {
        fn f(&self) {
            println!("ok 2");
        }
    }
}

fn main() {
    use a::Tr;

    test1::S.f();
    test2::S.f();
}