Shadowing traits via use emits no warnings/errors

[hoelzro]

The following code compiled with Rust dc4560d:

use Set = std::hashmap::HashSet;

fn main() {
    let set : Set<int> = Set::new();
    set.contains(&3);
    let _ = set;
}

fails to compile with the following message:

/tmp/test2.rs:5:4: 5:21 error: type `std::hashmap::HashSet<int>` does not implement any method in scope named `contains`
/tmp/test2.rs:5     set.contains(&3);
                        ^~~~~~~~~~~~~~~~~

With the help of the wonderful folks on #rust, I was able to determine that the reason is isn't working is that the Set trait is being masked by my alias for std::hashmap::HashSet. I think that the compiler should emit a warning or error to explain what's going on.

[bstrie]

I think there's a question as to what the proper behavior is here.

Nominating for Well-Defined.