pub(restricted) produces misleading diagnostic for private type in public interface lint

[strega-nil]

pub struct DoopGeneral<T> {
  pub(crate) var: T,
}
pub type Doop = DoopGeneral<Inner>;
pub(crate) struct Inner;

fails with error: private type in public interface [E0446]

https://play.rust-lang.org/?gist=35cee8425ac59ef27aa8898bd6343083&version=nightly&backtrace=0

[petrochenkov]

The error itself is correct, but the error messages are not updated yet.
Doop and Inner don't have the same scope (visibility), Doop is pub so its visibility is "all crates", Inner is pub(crate) so its visibility is "this crate".
Items with visibility v can't use items with visibilities v' < v in their interfaces.

[strega-nil]

@petrochenkov Oh, I see what you mean. This is... kinda annoying? But at least I understand it now.

[steveklabnik]

/cc #32409

[estebank]

The current output has better wording:

error[E0446]: private type `Inner` in public interface
 --> src/main.rs:6:1
  |
6 | pub type Doop = DoopGeneral<Inner>;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't leak private type

It should probably be expanded to be

error[E0446]: private type `Inner` in public interface
 --> src/main.rs:6:1
  |
6 | pub type Doop = DoopGeneral<Inner>;
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ can't leak private type
7 | pub(crate) struct Inner;
  | ----------------------- private type being leaked