Add an option to save the json output from rustc to pass to rust-analyzer

[matts1]

@googleson78 originally wrote #1657 in order to solve this problem. As discussed in that PR, they're no longer working on this, so I offered to pick this up. This is the same PR as that one, but has some bugfixes and refactoring applied.

[UebelAndre]

Hi! Thanks for working on this!

Would you be able to show how rust-analyzer could consume this? My understanding is that this would allow your IDE to inline errors in the code? Similar to the cargo check behavior. But according to #1633 there isn't any hook in rust-analyzer for this yet or there may not be? Is that correct?

[matts1]

We'd use a custom vscode extension (I've published it here) for bazel + rust (I talked to rust-analyzer folks, and they agreed that all non-cargo build systems should probably write their own rust-analyzer.

I have a prototype with everything working here, but the TLDR is:

1. A custom flycheck would be registered for rust-analyzer that just cats the output of concatenated.rustc-output (which will be generated by gen-rust-project)
2. Vscode extension would query a list of open files, and invoke bazel run @rules_rust//tools/gen-rust-project -- --files <currently open files in vscode>
3. gen-rust-project would convert those files to bazel targets
4. gen-rust-project would use bazel cquery to calculate the rustc-output files.
5. gen-rust-project would output a rust-project.json for the bazel targets from step 3
6. gen-rust-project would watch for changes to any of those files from step 4
7. When gen-rust-project sees a change, it concatenates all the files from step 4 together to concatenated.rustc-output, then writes a line to stdout, which the vscode extension then receives.
8. When the vscode extension receives the message, it invokes the vscode command clear flychecks and then the command run flychecks.

[purkhusid]

@matts1 Have you been using this patch successfully in your project?

[matts1]

Yeah, it's been working fine for me.

[Silcet]

I'm crazy interested in this one, but I can see it has stalled a bit. Can I help somehow? I have forked the repo and rebased your changes to solve the conflicts, so I could submit my branch if that helps... 😃

[matts1]

@UebelAndre Could you please take a look again. CI is failing for unrelated reasons (unsupported toolchain 'ubuntu1604-bazel-java8'). It appears someone removed the old version of java from RBE.

You can try it out by the following:

cd examples/bzlmod/hello_world
bazel build //:hello_world --@rules_rust//:output_diagnostics=true --output_groups=+rustc_output,+rustc_rmeta_output

You should then see a bazel-bin/hello_world.rustc_output file in addition to the regular bazel-bin/hello_world

[purkhusid]

I think this would be awesome to get this change in, any chance that any of the maintainers could give it some time?

[matts1]

I just fixed the merge conflicts, so it should be good to go as soon as it gets approved.

[matts1]

@UebelAndre Your changes requested doesn't appear to be actual changes, but I can't work out how to resolve that from github's perspective. Should be fine to review.

[UebelAndre]

Sorry for the delay here. I think this seems good 😄. Just one question.

[purkhusid]

Any chance we can get this on main?

[UebelAndre]

Sorry for the delay here 😅

I think this looks good by my final request would be updating //docs:rust_analyzer.vm to describe the steps mentioned here: #1942 (comment)

[matts1]

@UebelAndre Should be good to go

[UebelAndre]

Thanks!