Methods that return unsized types can be (uselessly) codegened

[arielb1]

trait Foo {
    fn foo(&self) -> [u8];
}

fn foo(f: Option<&Foo>) {
    if let Some(f) = f {
        let _ = f.foo();
    }
}

fn main() { foo(None) }

This does generate code that calls foo in the vtable, but is not particularly useful.

cc @nikomatsakis

[brson]

Still a problem?

[nikomatsakis]

It's still true, but I'm not especially worried about it.

[durka]

Isn't it a bug that you can declare such a trait at all? There's no way to implement it, right?

[jonas-schievink]

This code is now rejected with:

error[E0161]: cannot move a value of type [u8]: the size of [u8] cannot be statically determined
 --> src/main.rs:7:17
  |
7 |         let _ = f.foo();
  |                 ^^^^^^^

error: aborting due to previous error