error[E0599]: no method named `unwrap` found for type `std::result::Result<(), Foo>` in the current scope
  --> $DIR/method-help-unsatisfied-bound.rs:15:7
   |
15 |     a.unwrap();
   |       ^^^^^^
   |
   = note: the method `unwrap` exists but the following trait bounds were not satisfied:
           `Foo : std::fmt::Debug`

error: aborting due to previous error