Custom java_toolchain conflicting with protobuf's :java_toolchain

[ejona86]

We (gRPC) have a user that is using a custom java_toolchain that fails the build on warnings. The Bazel protobuf integration compiles google/protobuf from source, which currently triggers some warnings. So the user is unable to use their java_toolchain with gRPC/protobuf and was wanting gRPC/protobuf to use pre-built JARs instead of from-source compilation.

How should first-class Java dependencies be handled in Bazel?

More information can be found at grpc/grpc-java#3412

CC @pgr0ss @buchgr @cgrushko

[cgrushko]

Bazel protobuf integration compiles google/protobuf from source

Not exactly - it takes whatever label you give it in --proto_compiler and "builds" it. If it's a precompiled binary there won't be any compilation.

So a trivial solution is to build the proto compiler (either with Bazel or whatever) and check-in the binary.
The harder solution is to complain to github.com/google/protobuf.

I'm unaware of a mechanism to suppress warnings from external repositories, though there might be; perhaps file a separate issue about that?

[hlopko]

Did anybody talk to the protobuf people?

[drigz]

This has been fixed (protocolbuffers/protobuf#4220) but has not been ported from master into the 3.5.x branch, so I guess we can wait for 3.6.0 or use HEAD.

[rockwotj]

@cgrushko --proto_compiler doesn't actually fix the problem due to #8485

[comius]

I created a reproduction described in grpc/grpc-java#3412, here: https://github.com/comius/bazel_issue_3757.

It compiles without any warnings on bazel 3.7.2.

[comius]

There was no response for "more data needed". I'm closing the issue.