Error code E0742

Visibility is restricted to a module which isn’t an ancestor of the current item.

Erroneous code example:

pub mod sea {}

pub (in crate::sea) struct Shark; // error!

fn main() {}

To fix this error, we need to move the Shark struct inside the sea module:

pub mod sea {
    pub (in crate::sea) struct Shark; // ok!
}

fn main() {}

Of course, you can do it as long as the module you’re referring to is an ancestor:

pub mod earth {
    pub mod sea {
        pub (in crate::earth) struct Shark; // ok!
    }
}

fn main() {}