Importing private reexports does not work

[emberian]

Testcase:

#![crate_type = "lib"]

use std::vec::Vec as Vec;

mod foo {
    use Vec;
}

This should seemingly go through with no issue, but instead:

rustc output:

foo.rs:6:9: 6:12 error: unresolved import `Vec`. There is no `Vec` in `???`. Did you mean to use `Vec`? [E0432]
foo.rs:6     use Vec;
                 ^~~
foo.rs:6:9: 6:12 help: run `rustc --explain E0432` to see a detailed explanation
error: aborting due to previous error

[emberian]

Same error:

#![crate_type = "lib"]

use std::vec::Vec;

mod foo {
    use Vec;
}

#![crate_type = "lib"]

use std::vec::Vec as Foo;

mod foo {
    use Foo;
}

[emberian]

If we don't want to support this feature (which is useful for no_std crates to switch between std modules and non-std modules), the error message should be more specific.

[petrochenkov]

This is "by design" currently, but it's being fixed in #32213 (which probably needs an RFC before merging).