error[E0277]: the trait bound `U: std::marker::Copy` is not satisfied
  --> $DIR/wf-struct-bound.rs:10:14
   |
LL | trait ExtraCopy<T:Copy> { }
   | ----------------------- required by `ExtraCopy`
...
LL |     where T: ExtraCopy<U>
   |              ^^^^^^^^^^^^ the trait `std::marker::Copy` is not implemented for `U`
   |
help: consider restricting this type parameter with `where U: std::marker::Copy`
  --> $DIR/wf-struct-bound.rs:9:21
   |
LL | struct SomeStruct<T,U>
   |                     ^

error: aborting due to previous error

For more information about this error, try `rustc --explain E0277`.