We permit type parameters and so forth on builtin bounds

[nikomatsakis]

Example:

fn foo<T:Copy<U>, U>(x: T) {
}

fn main() {
}

I left a FIXME at the relevant part of the code.

[nikomatsakis]

Nominating for something.

[flaper87]

I can mentor...

[richo]

I'm willing to have a look if the mentor offer stands @flaper87

[ahmedcharles]

I already have a proposed fix, I just need to clean it up and add a test.

[flaper87]

@richo thanks for volunteering. The offer is still up but @ahmedcharles has been working on it. I'm happy to help with other bugs too.