Unecessarily public item

What it does

Lint items that are exported as pub, but are not used outside of the module they're defined in.

Advantage

Ensure code is not more public than it needs to be, enforcing abstraction boundaries

Drawbacks

High possibility of false positives. Should be in the pedantic category, and have some heuristics for ignoring items that are intended to be exported from the crate to other crates (eg don't lint on items exported from lib.rs or prelude.rs)

Example

mod foo {
    pub fn f() {}

    pub fn g() { 
        f()
    }
}

Could be written as:

mod foo {
    fn f() {}

    pub fn g() { 
        f()
    }
}

Start by reviewing the issue's Rust examples and the proposed exceptions for lib.rs and prelude.rs. Determine how a pedantic lint would identify pub items used only within their defining module and how it would avoid likely false positives. Done means the lint enforces narrower visibility while handling the stated export heuristics.