The compiler should report publicly exported type names if possible

[pcwalton]

If a private type is reexported at some public location, the Rust compiler will report the private location when referring to the type. It'd be more helpful if the compiler reported the public alias for it.

This was reported by Coda Hale on Twitter.

---

Update by pnkfelix: here is a standalone bit of code illustrating the problem. (play):

mod a {
    mod m { pub struct PrivateName; }
    pub use m::PrivateName as PublicName;
}

fn main() {
    // a::m::PrivateName; // would error, "module `m` is private"
    a::PublicName;
    a::PublicName.clone();
}

As of nightly 2019-06-17, this issues the diagnostic:

> error[E0599]: no method named `clone` found for type `a::m::PrivateName` [...]
                                                        ^^^^^^^^^^^^^^^^^
                                                                 |
             (author of `fn main` wants to see `a::PublicName` here)

[steveklabnik]

This happens a lot with core/std.

[steveklabnik]

Triage: it seems like a private type can no longer be exported as a public type at all

pub mod A {
    struct Foo;
    pub use A::Foo as Bar;
}

fn main() {
    let b = A::Bar;
}

gives

hello.rs:5:13: 5:26 error: `Foo` is private, and cannot be reexported [E0364]
hello.rs:5     pub use A::Foo as Bar;
                       ^~~~~~~~~~~~~
hello.rs:5:13: 5:26 help: run `rustc --explain E0364` to see a detailed explanation
hello.rs:5:13: 5:26 note: consider marking `Foo` as `pub` in the imported module
hello.rs:5     pub use A::Foo as Bar;
                       ^~~~~~~~~~~~~

So I believe this is effectively fixed? My core/std comment is more about reexports where both are public:

pub mod A {
    pub struct Foo;
    pub use A::Foo as Bar;
}

fn main() {
    let b: i32 = A::Bar;
}

which gives

hello.rs:9:18: 9:24 error: mismatched types:
 expected `i32`,
    found `A::Foo`
(expected i32,
    found struct `A::Foo`) [E0308]
hello.rs:9     let b: i32 = A::Bar;
                            ^~~~~~
hello.rs:9:18: 9:24 help: run `rustc --explain E0308` to see a detailed explanation
error: aborting due to previous error

which is covered by another ticket whose number escapes me.

[petrochenkov]

The issue is relevant to "unnameable" pub types which are still allowed.

mod m {
    pub struct PrivateName;
}

pub use m::PrivateName as PublicName.

m::PrivateName is still used in error messages, while it's preferable to use PublicName.

[torkleyy]

It also reports names which don't exist:

Consider this library:

// lib.rs of crate foo

mod a {
    pub trait Foo {}
}

pub use a::Foo as Afoo;

pub fn foo<T: Afoo>() {}

And some binary crate using it:

extern crate foo;

use foo::foo;

fn main() {
    foo::<()>(); // Afoo is not implemented for `()`
}

The error message is:

error[E0277]: the trait bound `(): foo::Foo` is not satisfied
 --> src/main.rs:6:5
  |
6 |     foo::<()>();
  |     ^^^^^^^^^ the trait `foo::Foo` is not implemented for `()`
  |
  = note: required by `foo::foo`

So it does not report the private name but a name that does not exist.