Bazel 9 Upstream Prebuilt Protobuf
Work in collaboration with the Google Protobuf team
Bazel 9.0 is a major long-term support (LTS) release. It contains new features and backwards incompatible changes.
Bzlmod is now always enabled, and all WORKSPACE logic has been removed from Bazel (#26131). The Bzlmod migration tool is available.
All C++-related rules are removed from Bazel and must be loaded from @rules_cc, as part of the Starlark effort.
Bazel 9 ships with the latest protobuf module (version 33.4), which includes support for a prebuilt protobuf compiler.
This prebuilt protobuf compiler follows up on our blog article https://blog.aspect.build/never-compile-protoc-again which ended with the promise “We’re hoping to upstream our toolchains_protoc to the protobuf repository, so that the default Bazel experience will be fast.”
This is now (nearly) true as of the https://github.com/protocolbuffers/protobuf/releases/tag/v33.4 release.
We thank the Google Protobuf team for sponsoring this work and reviewing the implementation, including changes to the release process.
Enabling the Protobufs toolchains feature
Bazel 9 flips the --incompatible_enable_proto_toolchain_resolution flag to true. This means Bazel is responsible for resolving the symbol @protobuf//bazel/private:proto_toolchain_type to a “concrete” toolchain that provides the right protoc binary for your execution platform. This is also the case for a toolchain_type for each language stub generator.
If you’re on Bazel 9, there’s nothing to do, but earlier Bazels require you set the flag.
Opting-in
Until https://github.com/protocolbuffers/protobuf/pull/25313 lands and is released, you need to opt-in to using the protoc binaries from https://github.com/protocolbuffers/protobuf/releases. Add to your .bazelrc:
common --@protobuf//bazel/toolchains:prefer_prebuilt_protoc
note, if you have a
repo_name=com_google_protobufyou’ll have to adapt the@protobufname
Enforcing
You can enforce that no rules do the “Wrong Thing” of directly referencing the cc_binary target @protobuf//:protoc by following our snippets: https://github.com/aspect-build/toolchains_protoc#ensure-protobuf-and-grpc-never-built
If this fails to build, it means that there’s a bug you should find or report.
The https://github.com/aspect-build/toolchains_protoc and https://github.com/bazelbuild/rules_proto repositories are now archived, completing the deprecation period.
Next
Need help migrating from WORKSPACE to Bzlmod or other steps to move to Bazel 9? View Aspect Build services and email us at hello@aspect.build or ping us on Bazel Slack. We’re happy to support you.
