[FR]: multiple protobuf versions

[gfrankliu]

What is the current behavior?

Our github monorepo uses bazel 7 (bzlmod) and has a mixture of C++, golang and python codes. Some protos are shared commonly. protobuf versions are defined separately (MODULE.bazel, go.mod, requirements.txt). Python codes use tensorflow 2.15 which has a lock on the old protobuf 3.2x. When we upgrade grpc version in MODULE.bazel which implicitly upgrade protobuf version, it breaks our python codes.

Describe the feature

Can toolchains_protoc be used to support multiple protobuf versions? Is it possible to use toolchains_protoc with older version of protoc (3.2x) so that the compiled proto files can be used by any newer versions of protobuf? This means we can use newer version of protobuf in MODULE.bazel while keeping the old version of protobuf in requirements.txt.

[alexeagle]

It is possible, however we are working with the protobuf team and @jguamie to upstream this repo and there is some design discussion currently about whether to permit this or not. Having your use case available will help motivate the design.

[gfrankliu]

Thanks @alexeagle !
For now I tried this hack which seems to work. Can we hack toolchains_protoc to create to have two instances, protoc1 and protoc2, each pointing to a different version, and then use one for python, and one for the rest?