error-chain -> thiserror port

[databasedav]

No description provided.

[databasedav]

@khaf i believe i'm almost done here but need some guidance on a few things

• what to do about log_error_chain? the thiserror Error type doesn't expose a .backtrace method like error-chain does, although i believe we can get a similar effect with Backtrace::force_capture
• how to handle error contexts? this was builtin to error-chain with the .chain_err method, which thiserror doesn't have an analog for, and while anyhow does have "context" methods which serve the same purpose, they return anyhow::Error wrappers as opposed to raw the concrete error from thiserror, which relates to the last concern ...
• i went ahead and replaced the bail! calls with return Err to avoid either 1. creating a custom bail! just for this library, or 2. having to introduce anyhow which has a general bail!, which would similarly have the negative of introducing another crate that add another layer to the thiserror error enum

[khaf]

@databasedav Thanks for the quick turn around! I looked around for a few hours and from what I understand thus far:

1. There is no easy workaround. thiserror uses an unstable feature for backtraces that until final release can only be used via nightly. I have not been able to come up with a solution myself. Maybe @jonas32 can chime in.
2. We have to implement it ourselves. This example could be helpful: https://github.com/jsvana/async-minecraft-ping/pull/8/files
3. No need for bail!. The idea with moving to thiserror was to have idiomatic error handling.

[databasedav]

@khaf thoughts on using error-stack? i'm not a big fan of how the "context nesting" strategy pollutes the library level with having to deal with the Generic/WithContext error wrappers, embedding the context api into the error struct with a trait is much cleaner/more idiomatic imo

[khaf]

@databasedav I'm pretty sure I had answered this right away, but seeing that my response is missing, I assume I left to research and reflect and forgot to come back to it. Sorry about that.

I have nothing against the error-stack. As long as the library does not impose runtime cost, leaking abstractions and limitation upon us, I'm fine with it.

I'm open to the idea, let me know how it goes.

[khaf]

@databasedav I have updated this PR to finish the work you started. The code compiles now.
Having looked at error-stack, it shares an issue with anyhow in that it shows up in the public API. It is also too complicated for our needs, and has a much smaller user base in comparison to thiserror. The current implementation is not complete, since I'd like to add backtrace and source to all errors to easy debugging, but I think we are on the right track.
To chain errors, I have introduced a Wrapped option, which boxes errors inside in a chain. I will have to rename it to something better (Chain maybe? Open to suggestions) and implement some public API to allow easy introspection.
Let me know what you think.