Update tonic, prost, and protobufs

[iczero]

Updating prost in xds-api causes a catch-22 situation where the crate needs to be built in order to run generate_sources (which is a test), but the crate cannot be built since the new prost is not API-compatible with the old generated code. I have added a generate_only internal feature to be used when prost-build needs to be run for a breaking prost upgrade. This effectively disables pretty much the entire crate.

XDS_API_SKIP_GEN_SRC_DIRTY_CHECK=1 PROTOC="/path/to/protoc-31.1/bin/protoc" \
  cargo test --features generate_only -- generate_sources

Additionally, opencensus was removed because it is gone from upstream: envoyproxy/data-plane-api@040c2d8, and generate_sources now checks the PROTOC env var.

Please note that I have not tested this except for cargo test. It may be best to not merge yet.

[blinsay]

Thanks for taking a look!

This is definitely something we've also run into but haven't had a reason to come clean up yet. I'm not inclined to merge this, since I think we can do better than the feature - I've been thinking about moving codegen back out of the tests and either back into build.rs or into a separate xtask crate.

Before I do any of that, are you also actively interested in the protoc upgrade or was that just a nice-to-have while upgrading everything else?

[blinsay]

I should also ask: are you interested in just the protobufs or in the tonic api as well? I've been thinking about whether or not it's useful to split those into separate features.

[iczero]

The protoc upgrade was indeed just a nice to have. I personally am interested in using the tonic APIs.

In git history I saw that the generation step was previously in an xtask. Is there a reason it was moved into a test? I assumed it wasn't in build.rs since that would run generation on install and hence require the correct protoc version to be present.

[blinsay]

In git history I saw that the generation step was previously in an xtask. Is there a reason it was moved into a test?

I don't remember why we decided not to do an xtask at the time, but do remember borrowing the test approach from tokio-console. I'll put up a PR in the next couple days with the generation moved back into an xtask and go from there.

Thanks for opening the PR!

[blinsay]

Sorry about the delay - should have time to start landing all of this shortly.