error[E0046]: not all trait items implemented, missing: `Output`
  --> $DIR/issue-23827.rs:36:1
   |
36 |   impl<C: Component> FnOnce<(C,)> for Prototype {
   |  _^ starting here...
37 | |     //~^ ERROR E0046
38 | |     //~| NOTE missing `Output` in implementation
39 | |     //~| NOTE `Output` from trait: `type Output;`
40 | |     extern "rust-call" fn call_once(self, (comp,): (C,)) -> Prototype {
41 | |         Fn::call(&self, (comp,))
42 | |     }
43 | | }
   | |_^ ...ending here: missing `Output` in implementation
   |
   = note: `Output` from trait: `type Output;`

error: aborting due to previous error