error[E0277]: the trait bound `Self: std::cmp::Eq` is not satisfied
  --> $DIR/wf-trait-default-fn-arg.rs:11:22
   |
LL | struct Bar<T:Eq+?Sized> { value: Box<T> }
   |              -- required by this bound in `Bar`
...
LL |     fn bar(&self, x: &Bar<Self>) {
   |                      ^^^^^^^^^^ - help: consider further restricting `Self`: `where Self: std::cmp::Eq`
   |                      |
   |                      the trait `std::cmp::Eq` is not implemented for `Self`

error: aborting due to previous error

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