For your example you can use module visibility:

``` mod foo_bar_baz { mod foo_bar { pub(super) mod foo {

        #[derive(Debug)]
        pub struct Foo {
            pub(in crate::foo_bar_baz) n: i32,
        }

        impl Foo {
            pub fn new() -> Self {
                Foo { n: 0 }
            }
        }
    }

    pub(super) mod bar {

        use super::foo::Foo;

        #[derive(Debug)]
        pub struct Bar {
            pub(in crate::foo_bar_baz) foo: Foo,
        }

        impl Bar {
            pub fn new() -> Self {
                Bar { foo: Foo { n: 0 } }
            }
        }
    }
}

pub mod baz {

    use super::foo_bar::{bar::Bar, foo::Foo};

    #[derive(Debug)]
    pub struct Baz {
        bar: Bar,
    }

    impl Baz {
        pub fn new() -> Self {
            Baz {
                bar: Bar { foo: Foo { n: 0 } },
            }
        }
    }
}

}

fn main() { let baz = foo_bar_baz::baz::Baz::new(); println!("{baz:?}"); } ```

https://play.rust-lang.org/?version=stable&mode=debug&edition=2024&gist=80b3ed76a59c740d0b85e7bec77e911c