Trait inheritance doesn't work with the Copy trait

[erickt]

While trait inheritance works with user defined traits, it doesn't appear to work with special traits like Copy. This code compiles fine:

trait Foo       { fn f(&self); }
trait Bar: Foo  { fn g(&self); }
trait Baz: Copy { fn h(&self); }

struct A;

impl Foo for A { fn f(&self) { } }
impl Bar for A { fn g(&self) { } }
impl Baz for A { fn h(&self) { } }

fn f<T: Bar>(t: &T) {
    t.f();
    t.g();
}

fn g<T: Baz+Copy>(t: T) -> T {
    t.h();
    copy t
}

/*
fn h<T: Baz>(t: T) -> T {
    t.h();
    copy t
}
*/

fn main() { }

However, if you uncomment function h, it errors with:

foo.rs:23:9: 23:10 error: copying a value of non-copyable type `'a`
foo.rs:23     copy t
                   ^
foo.rs:23:9: 23:10 note: explicit copy requires a copyable argument
foo.rs:23     copy t
                   ^
error: aborting due to previous error

[erickt]

This was based off of an issue @lifthrasiir mentioned in IRC.

[catamorphism]

Yes, this functionality isn't implemented yet. Sorry! Follow #3984 to see progress.