protoc "--go_out: protoc-gen-go: plugins are not supported" in CI

By Daniel Zoghalchali·Latchkey

The modern google.golang.org/protobuf version of protoc-gen-go dropped the old plugins=grpc option. gRPC stubs are now generated by a separate protoc-gen-go-grpc plugin, so --go_out=plugins=grpc:... is rejected.

What this error means

protoc fails with "--go_out: protoc-gen-go: plugins are not supported" the moment you pass plugins=grpc to the Go output.

--go_out: protoc-gen-go: plugins are not supported

Common causes

Legacy plugins=grpc syntax with the new plugin

The command still uses --go_out=plugins=grpc:., which only the old github.com/golang/protobuf plugin understood. The current plugin removed that mode.

A mix of old build scripts and a new plugin install

CI installs the modern protoc-gen-go but the Makefile or script predates the split into two plugins.

How to fix it

Split into two output directives

1. Install protoc-gen-go-grpc alongside protoc-gen-go.
2. Replace --go_out=plugins=grpc:. with separate --go_out and --go-grpc_out flags.
3. Re-run protoc to generate message and gRPC code.

protoc -I proto \
  --go_out=. --go_opt=paths=source_relative \
  --go-grpc_out=. --go-grpc_opt=paths=source_relative \
  proto/service.proto

Express both plugins in buf.gen.yaml

A buf generate config makes the two-plugin split explicit and reproducible.

version: v1
plugins:
  - plugin: go
    out: gen/go
    opt: paths=source_relative
  - plugin: go-grpc
    out: gen/go
    opt: paths=source_relative

How to prevent it

• Use the two-plugin model (go plus go-grpc) in all generation scripts.
• Pin both plugin versions so the option surface stays stable.
• Migrate Makefiles off plugins=grpc when adopting the modern plugin.

Frequently asked questions

Related guides

References

• GitHub Actions documentation