error[E0599]: no method named `unwrap` found for type `std::result::Result<(), Foo>` in the current scope
  --> $DIR/method-help-unsatisfied-bound.rs:5:7
   |
LL |     a.unwrap();
   |       ^^^^^^ method not found in `std::result::Result<(), Foo>`
   |
   = note: the method `unwrap` exists but the following trait bounds were not satisfied:
           `Foo : std::fmt::Debug`

error: aborting due to previous error

For more information about this error, try `rustc --explain E0599`.