Errors: thiserror + anyhow instead of failure

[kim]

Fixes #72

Note that this is on top of #70

[kim]

I'm a bit unsure about the backtrace support -- failure adds them automatically, whereas thiserror apparently requires the error variant to have a field of type Backtrace, which would add quite a bit of annoying boilerplate. Otoh, backtraces are extremely valuable for ExceptT-style error handling. I might be misunderstanding how this works, though.

[FintanH]

I'm a bit unsure about the backtrace support -- failure adds them automatically, whereas thiserror apparently requires the error variant to have a field of type Backtrace, which would add quite a bit of annoying boilerplate. Otoh, backtraces are extremely valuable for ExceptT-style error handling. I might be misunderstanding how this works, though.

There's a curious paragraph in anyhow:

A backtrace is captured and printed with the error if the underlying error type does not already provide its own. In order to see backtraces, they must be enabled through the environment variables described in std::backtrace:

The way I read this is that they should be added automatically via anyhow as well. We would only add backtrace for the convenience of other downstream users 🤷‍♂️

[FintanH]

LGTM 👍 I'm going to try get the surf PR up to shape adding thiserror today :)