Associated types are *not* `Sized` when used in the return type of default methods

[japaric]

STR

#![feature(associated_types)]

trait Trait {
    type Output;

    // Here `Output` is `Sized`
    fn is(&self) -> Self::Output;
    // But, here it seems that `Output` it's no longer `Sized`
    fn isnt(&self) -> Self::Output {}
    //~^ error: the trait `core::kinds::Sized` is not implemented for the type `Output`
}

fn main() {}

Version

rustc 0.13.0-nightly (2a231594c 2014-12-18 12:21:57 +0000)

cc @nikomatsakis @nick29581