In-scope traits are leaking beyond imports

[alexcrichton]

pub mod a {
    pub trait A {
        fn foo(&self);
    }

}
pub mod b {
    use a::A;

    pub struct B;
    impl A for B { fn foo(&self) {} }

    pub mod c {
        use b::B;

        fn foo(b: &B) {
            b.foo(); // trait A is not in scope at this location
        }
    }

}

fn main() {}

That code compiles successfully, but I don't believe that it should. A the commented line, the trait A is not in scope for the module c, so I should get an error that b doesn't have any method named foo in scope.

Nominating, this is a backwards-compatibility issue.

[alexcrichton]

From what I could tell, it appeared that if any of your ancestors imported a trait, then it was automatically in-scope for any descendant. This seems like abstraction leakage which should be plugged.

[nikomatsakis]

Agreed, bogus.

[pnkfelix]

accepted for P-backcompat-lang.