error[E0599]: no method named `as_dyn_error` found for reference `&NotError` in the current scope
  --> $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 not found in `&NotError`
   |
   = note: the method `as_dyn_error` exists but 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`