`use`-ing a `pub` item from a private submodule points to the item as being private

[huonw]

use module::submod::{Trait, Struct, Static};

mod module {
    mod submod {
        pub trait Trait {}
        pub struct Struct;
        pub static Static: () = ();
    }
}

fn main() {}

bad-priv-error.rs:1:21: 1:26 error: trait `Trait` is private
bad-priv-error.rs:1 use module::submod::{Trait, Struct, Static};
                                         ^~~~~
bad-priv-error.rs:1:28: 1:34 error: type `Struct` is private
bad-priv-error.rs:1 use module::submod::{Trait, Struct, Static};
                                                ^~~~~~
bad-priv-error.rs:1:36: 1:42 error: static `Static` is private
bad-priv-error.rs:1 use module::submod::{Trait, Struct, Static};
                                                        ^~~~~~
error: aborting due to 3 previous errors

[alexcrichton]

Specifically here, these references are denied because submod is not public. It'd be nice to have a NOTE saying what needs to be flagged as public. There could possibly be a large chain of things which need to be public, but we can only point to the closest-to-the-definition one, which I think is OK anyway.

Also note that this will only work for local crate references, all external crate references don't have information about what the "closest private thing" was, or at least I don't think that they do...

[huonw]

Shouldn't it flag the submod directly as the cause of the error (since use module::submod is an error), rather than the leaves of the import?

That is to say, I'd rather the error message be:

error: module `submod` is private
use module::submod::{Trait, Struct, Static};
            ^~~~~~

than

error: trait `Trait` is private
use module::submod::{Trait, Struct, Static};
                     ^~~~~
note: module `submod` should be `pub`
use module::submod::{Trait, Struct, Static};
            ^~~~~~

(At least, if this isn't possible, it shouldn't say just is private, since the Trait is clearly pub trait.)