error[E0599]: the method `as_dyn_error` exists for reference `&NotError`, but its trait bounds were not satisfied
  --> $DIR/source-enum-not-error.rs:10:9
   |
4  | pub struct NotError;
   | --------------------
   | |
   | doesn't satisfy `NotError: AsDynError`
   | doesn't satisfy `NotError: std::error::Error`
...
10 |         source: NotError,
   |         ^^^^^^ method cannot be called on `&NotError` due to unsatisfied trait bounds
   |
   = note: the following trait bounds were not satisfied:
           `NotError: std::error::Error`
           which is required by `NotError: AsDynError`
           `&NotError: std::error::Error`
           which is required by `&NotError: AsDynError`
