Self is not recognised as implementing kinds in default method implementations

[chris-morgan]

(This is related to #7661. It is in fact the second case there, but moved into a new issue as it languished there with the rest fixed.)

fn require_send<T: Send>(_: T){}

trait TragicallySelfIsNotSend: Send {
    fn x(self) {
        require_send(self);
    }
}

fn main(){}

This does not compile, though it should:

<anon>:5:8: 5:20 error: instantiating a type parameter with an incompatible type `Self`, which does not fulfill `Send`
<anon>:5         require_send(self);
                 ^~~~~~~~~~~~
error: aborting due to previous error

I need this to be able to refer to self inside a spawn closure, and that will only work if it's Send, and so there I sadly cannot provide a default method implementation of the trait at present.

(buzzwords for search: built-in trait inheritance.)

[Aatch]

Nominating for a milestone, probably well-defined. We need some way of bounding the Self type inside default methods.

[catamorphism]

We think this is fixed. Marked as needstest.