A public fn in a private mod with a private type in its signature

[IvanUkhov]

If a crate has a private module and a private type, the module cannot have a public function whose signature refers to the private type. Here is an illustration:

type Baz = isize;

mod foo {
    use Baz;

    pub fn bar(_: Baz) { // error: private type in exported type signature
    }
}

The public function cannot presumably be qualified as a public-facing part of the crate, and it is not presumably a part of the public API of the crate.

Regards,
Ivan

[tomjakubowski]

You can use pub use Baz inside the foo module. The idea is that the identifier Baz inside the module foo is private to it; you might some day replace use Baz with something like type Baz = String and suddenly break users of that module without appearing to change any public signatures.

You could also write:

pub fn bar(_: super::Baz) {
}

[IvanUkhov]

@tomjakubowski, thank you for the response. There are no users of that module as the module is private to the crate. pub use Baz inside the module does not seem to help; the error in that case is error: Baz is private. super does not seem to help either. Could you please clarify what you have in mind?

[tomjakubowski]

There are users of the module inside the crate. I don't mean users in the sense of people using it, just that other pieces of code ("users") are using it.

Anyway, it looks like I've internalized some old rules of privacy or something. Whoops. My mistake.

[alexcrichton]

This is a dupe of #25532 and #25260, both of which are intended behavior, so closing (more details in those issues).