text: error[E0277]: the trait bound `U: Copy` is not satisfied
    --> $DIR/wf-struct-bound.rs:10:14
     |
  LL | trait ExtraCopy<T:Copy> { }
     |                   ---- required by this bound in `ExtraCopy`
  ...
  LL |     where T: ExtraCopy<U>
     |              ^^^^^^^^^^^^ the trait `Copy` is not implemented for `U`
     |
  help: consider further restricting type parameter `U`
     |
  LL |     where T: ExtraCopy<U>, U: Copy
     |                          ^^^^^^^^^
  
  error: aborting due to previous error
  
  For more information about this error, try `rustc --explain E0277`.
  