error[E0446]: private type `foo::Bar` in public interface
  --> $DIR/E0446.rs:4:5
   |
LL |       struct Bar(u32);
   |       - `foo::Bar` declared as private
LL | 
LL | /     pub fn bar() -> Bar {
LL | |         Bar(0)
LL | |     }
   | |_____^ can't leak private type

error: aborting due to previous error

For more information about this error, try `rustc --explain E0446`.