LYR-SEM0151

a declaration names a type less visible than itself

error · spec 04-modules

A declaration's signature or type names a type that is less visible than the declaration: a pub function returning an internal struct, an internal function taking a private one, a field, constant or inferred binding whose type is narrower than it.

Explanation

A declaration is no more visible than the types it names. Whoever may use origin must be able to name what it returns and what it takes; a pub function that hands out an internal type would give other packages a value they cannot write the type of. The check covers parameter and result types, field types, the types of constants and the inferred type of a binding.

Make the named type as visible as the declaration, or make the declaration narrower.

Wrong

struct Point {
    x: int,
}

pub fn origin(): Point {
    return Point { x = 0 };
}

fn main(): void {
    let _ = origin();
}

Right

pub struct Point {
    pub x: int,
}

pub fn origin(): Point {
    return Point { x = 0 };
}

fn main(): void {
    let _ = origin();
}