error[E0277]: the trait bound `&mut Baz: Happy` is not satisfied
  --> $DIR/multiple-1.rs:52:9
   |
LL | fn foo<T>(_: T) where T: Happy {}
   |                          ----- required by this bound in `foo`
...
LL |     foo(&mut baz);
   |         ^^^^^^^^ the trait `Happy` is not implemented for `&mut Baz`

error: aborting due to previous error

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