How to replace the custom_error feature

[Maaarcocr]

in #355 the custom_error flag was removed. Is there any substitute for such feature in the newer versions on wit-bindgen? Is this now unnecessary? If so, why?

If there is a plan to add something like this back, I would also be happy to spend some time trying to get it done!

[alexcrichton]

Pat's working on error-handling for wit-bindgen by prototyping this first in wiggle as part of bytecodealliance/wasmtime#5276 and bytecodealliance/wasmtime#5279 and I believe he plans on carrying over that work to this repository in short order.

[pchickey]

Yep I have the PR half-done right now, it should be up today or tomorrow

[Maaarcocr]

Thank you!!

[alexcrichton]

Looking back I think this was more-or-less done in #388 where Wasmtime-hosted functions by default return anyhow::Result<T> now where T is the result of the function and all other errors are traps. For result<_, _>-returning functions in *.wit that now translates to Resul<T, Error<E>> where Error<E> can be created from E or from anyhow::Error (more-or-less) where the former represents something to return to the guest and the latter represents a trap. You can implement custom From<MyType> for Error<E> conversions to weave custom errors into an E as necessary.