submodules can't access non-pub type names in parent modules

[jbclements]

For type names only, submodules can't apparently see non-pub types defined in the parent module. So, this code:

struct Name { x : int }

mod test {
    use super::Name;

    #[test] fn f () {
        let a : Name = Name { x : 3};
    }    
}

... generates this error:

jclements-09740:/tmp clements> rust test /tmp/foo.rs
Running /usr/local/bin/rustc:
/tmp/foo.rs:4:8: 4:20 error: failed to resolve import: super::Name
/tmp/foo.rs:4     use super::Name;
                      ^~~~~~~~~~~~
error: failed to resolve imports
error: aborting due to 2 previous errors

[luqmana]

Now it at least tells you that Name is private:

-> % rustc bar.rs
bar.rs:4:8: 4:19 error: unresolved import: found `Name` in `???` but it is private
bar.rs:4     use super::Name;
                 ^~~~~~~~~~~
bar.rs:4:8: 4:19 error: failed to resolve import `super::Name`
bar.rs:4     use super::Name;
                 ^~~~~~~~~~~
error: aborting due to 2 previous errors

Though, it doesn't need to display the error twice and could do better than ???.

[pnkfelix]

linking to #6143 for unified tracking of resolve

[alexcrichton]

Closing as a dupe of #8215, this would be allowed with the rules in that bug.