Rust error E0445: #### Note: this error code is no longer emitted by the compiler

The compiler team's explanation

Note: this error code is no longer emitted by the compiler.

A private trait was used on a public type parameter bound.

Previously erroneous code examples:

trait Foo {
    fn dummy(&self) { }
}

pub trait Bar : Foo {} // error: private trait in public interface
pub struct Bar2<T: Foo>(pub T); // same error
pub fn foo<T: Foo> (t: T) {} // same error

fn main() {}

To solve this error, please ensure that the trait is also public. The trait can be made inaccessible if necessary by placing it into a private inner module, but it still has to be marked with pub. Example:

pub trait Foo { // we set the Foo trait public
    fn dummy(&self) { }
}

pub trait Bar : Foo {} // ok!
pub struct Bar2<T: Foo>(pub T); // ok!
pub fn foo<T: Foo> (t: T) {} // ok!

fn main() {}

From rustc --explain E0445 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.