error[E0277]: the trait bound `T: Copy` is not satisfied
  --> $DIR/wf-in-fn-ret.rs:10:16
   |
LL | fn bar<T>() -> MustBeCopy<T>
   |                ^^^^^^^^^^^^^ the trait `Copy` is not implemented for `T`
   |
note: required by a bound in `MustBeCopy`
  --> $DIR/wf-in-fn-ret.rs:6:21
   |
LL | struct MustBeCopy<T:Copy> {
   |                     ^^^^ required by this bound in `MustBeCopy`
help: consider restricting type parameter `T`
   |
LL | fn bar<T: std::marker::Copy>() -> MustBeCopy<T>
   |         +++++++++++++++++++

error: aborting due to 1 previous error

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