A private trait was used on a public type parameter bound.
Erroneous code examples:
```compile_fail,E0445
#![deny(private_in_public)]
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() {}
```