protoc version

[jjh42]

Description

Is there some way to easily select the version of protoc that is used.

The issue is that I need to use protoc that generates python version 4 files
https://protobuf.dev/support/version-support/
since almost all python dependencies are still on that version.

But I can't figure out how to do this.

[sschnug]

I also currently look into the new bzlmod-based version of rules-proto-grpc and the protobuf cross-runtime guarantee topic.

Consider trying out the following:

• Follow the setup in https://rules-proto-grpc.com/en/stable/lang/cpp.html#installation -> protoc.toolchain
  • C++ has no cross-runtime guarantees and therefore this explicit setting is extremely important (and maybe for this reason it's only to be found in the c++ example!)

Now is this respected in other toolchains? -> Yes!

• version = "v27.1" -> produces python with header docstrings containing # Protobuf Python Version: 5.27.1
  • proof of correct core <-> language mapping: https://github.com/protocolbuffers/protobuf/blob/v27.1/version.json
• version = "v26.0" -> # Protobuf Python Version: 5.26.0
  • https://github.com/protocolbuffers/protobuf/blob/v26.0/version.json
• version = "v25.4" -> # Protobuf Python Version: 4.25.4 !!!!!
  • https://github.com/protocolbuffers/protobuf/blob/v25.4/version.json

Now the versions you can pick from must be pre-registered afaik (aka it fails for example with 25.5). It seems the source of truth here is https://github.com/aspect-build/toolchains_protoc/blob/main/protoc/private/versions.bzl