error[E0599]: the method `as_dyn_error` exists for struct `NotError`, but its trait bounds were not satisfied
  --> tests/ui/source-struct-not-error.rs:9:5
   |
4  | struct NotError;
   | ---------------
   | |
   | method `as_dyn_error` not found for this struct
   | doesn't satisfy `NotError: AsDynError`
   | doesn't satisfy `NotError: std::error::Error`
...
9  |     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`
note: the following trait must be implemented
  --> $RUST/core/src/error.rs
   |
   | pub trait Error: Debug + Display {
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^