Rust: Move to using annotate-snippets-rs for producing snippets

[Manishearth]

@zbraniecki created https://github.com/zbraniecki/annotate-snippets-rs which basically does Rust-style formatting of code snippets for errors, to be used within Fluent.

I think we should try and move our snippet code out of tree, preferably merging it with annotate-snippets-rs (which is already close to what rustc does), so that it's reusable.

@zbraniecki has agreed to make whatever changes necessary to the crate to make it usable within rustc.

cc @estebank

[oli-obk]

cc @rust-lang/wg-diagnostics

[oli-obk]

We just had our first wg-diagnostics meeting and think that a good first step would be to create a new (unstable) diagnostics renderer (we have json, short and human right now). Basically it would use the existing diagnostics backend to call into annotate-snippets.

We can then create a way to run ui tests with the new backend and see how the output changes and circle back to changing annotate-snippets until we are happy.

And once we are all happy, we can get rid of the old human emitter and replace it with the new annotate-snippets based one.

@zbraniecki in order to be able to use this in rustc, we'd need to move your crate into the rust-lang organization and give publish rights to some compiler devs so that we have quick access to it if anything needs doing. Are you ok with that?

[zbraniecki]

Yes! I'd love to hand it over to the Rust team and would be happy to see contributions or hand over to new maintainer if that's better for you! I will continue using it for fluent-rs, but I feel like the crate supports all my direct needs while it will need more features for Rust I believe (since Rust errors are more complex!)

[Manishearth]

@zbraniecki if you give me admin access to the repo I can migrate it.

[zbraniecki]

Invited!

[Manishearth]

I can push but I can't move. Hmm.

Maybe transfer the repo to me and then I can transfer it to rust-lang?

[zbraniecki]

I tried to transfer to you

[Manishearth]

Done! https://github.com/rust-lang/annotate-snippets-rs

[phansch]

If no one else has picked this up yet, I'd be interested in working on this. I'm currently working on adding the new diagnostics error-format.

[zbraniecki]

I'm happy to help you brainstorm, or review or whatever is needed. :)

[phansch]

I figured I'd post a small status update as it has been a while since the last changes.

We currently have the AnnotateSnippetEmitterWriter that emits
basic diagnostics using the annotate-snippet library. This writer is
essentially taking rustc's Diagnostic and turns that into an
annotate-snippet::Snippet. Currently this doesn't include suggestions
(#61809) and that's the thing I've been working on and off, with some
help from @zbraniecki.

The main problem with turning rustc annotations into annotate-snippet
annotations is that rustc annotation spans are line-based (using
FileWithAnnotatedLines), whereas annotate-snippet
expects the annotation spans to be relative to the start of the provided
snippet.

There's currently two open WIP PRs for annotate-snippet that would make it
possible to provide line-based annotations. It would be great to make some
progress there as that means we won't have to convert from line-relative to
snippet-relative annotation spans in our emitter.

Once annotation support has landed for the new emitter it would be a good time
to see where the output differs the most and what the next steps are.