#[source] does not work on Box<dyn Error + Send + Sync>

[bennetthardwick]

In order to get miette (with thiserror) to render the full error chain I need to be able to add the #[source] macro onto the "source" error.

In my project I'm using a boxed error that also needs to be Send + Sync like so:

#[derive(Diagnostic, Error)]
struct MyError {
  #[error("Any Error")]
  #[diagnostic(transparent)]
  AnyError(#[source] Box<dyn Diagnostic + Send + Sync>)
}

However that example fails with the following compilation error:

error[E0599]: the method `as_dyn_error` exists for reference `&Box<dyn Diagnostic + Send + Sync>`, but its trait bounds were not satisfied

20  |   pub trait Diagnostic: std::error::Error {
    |   ---------------------------------------
    |   |
    |   doesn't satisfy `dyn Diagnostic + Send + Sync: AsDynError<'_>`
    |   doesn't satisfy `dyn Diagnostic + Send + Sync: Sized`

I was able to get around the issue by using an Arc instead of a Box - but I don't need any Arc features so it would be great if it worked with Box.