Using miette in a middleware trait definition

[TheNeikos]

I currently have a trait akin to:

trait Middleware {
  fn handle(&self) -> Result<(), miette::Error>;
}

Which works fine until I try to use that Error in my own error reporting. I hit a couple of snags which I am not sure how to resolve:

1. Error does not implement Diagnostic or std::error::Error, meaning that I can't use it in #[related] nor in thiserror::Error #[source] annotations. I could implement Diagnostic myself, but this is particularly 'annoying' in my case since its a enum with a dozen of error kinds.
2. #[related] wants to see something that is IntoIterator but I usually just have a single error on which I want to add context. My current 'workaround' is to use a single element array, but it does look weird haha.

Now, these are just some painpoints I identified in this situation. I don't know if/how they come from my usage of the crate, but I still wanted to report my experience and potentially discuss solutions/changes that would make it easier to use here.

Thank you for making the crate!

[zkat]

1. This is correct, and intentional, because of How Type Stuff Works. Once you enter miette::Error (aka miette::Report) land, you can only downcast to specific errors. If you need to do this kind of thing, I suggest using a wrapper Diagnostic enum instead of miette::Error.
2. I have feelings about #[related]. I think the API could be much better, and there's been some discussion over at severity(warning) should probably not use an Error: introducer #139 (comment), but nothing specific has come up as of yet.

Thanks for the comments, and I'm glad you're enjoying the crate! Stuff like this is super welcome :)

[TheNeikos]

I agree that it is not straightforward, but since Diagnostic implements AsRef for Diagnostic it is technically possible. I don't know how it could be done in an automated fashion though.

[TheNeikos]

I've been thinking about your response @zkat, could you explain what you mean with a 'wrapper diagnostic enum'? I currently can't picture what you mean sadly.

I've also tried to use a Box<dyn Diagnostic> but I still can't use it as a source() since trait upcasting is still unstable in Rust :c

[zkat]

http-types has an interesting solution for this, for the sake of handling the same scenario (dealing with dynamic errors in middleware).

I don't know what the ideal solution here is. I admit it's hard and I don't have a good answer, but I think the above is a good direction to try and head in and see how it feels.

[TheNeikos]

I'd say that with the merging of #165 most of the pain points are gone and should work fine until the Provider API is there in some form. Thanks!