Protobuf

How to generate Go from Protocol Buffers.

---

When your Go code imports Protobuf generated files, Pants will detect the imports and run the Protoc compiler to generate then compile those files.

Example repository

See the codegen example repository for an example of using Protobuf to generate Go.

Benefit of Pants: generated files are always up-to-date

With Pants, there's no need to manually regenerate your code or check it into version control. Pants will ensure you are always using up-to-date files in your builds.

Thanks to fine-grained caching, Pants will regenerate the minimum amount of code required when you do make changes.

go mod tidy will complain about missing modules

Because Pants does not save generated code to disk, go mod tidy will error that it cannot find the generated packages.

One workaround is to run pants export-codegen :: to save the generated files.

Step 1: Activate the Protobuf Go backend

Add this to your pants.toml:

pants.toml

[GLOBAL]
backend_packages = [
  "pants.backend.experimental.codegen.protobuf.go",
  "pants.backend.experimental.go",
]

This adds the new protobuf_source target, which you can confirm by running pants help protobuf_source.

To reduce boilerplate, you can also use the protobuf_sources target, which generates one protobuf_source target per file in the sources field.

BUILD

protobuf_sources(name="protos", sources=["user.proto", "admin.proto"])

# Spiritually equivalent to:
protobuf_source(name="user", source="user.proto")
protobuf_source(name="admin", source="admin.proto")

# Thanks to the default `sources` value of '*.proto', spiritually equivalent to:
protobuf_sources(name="protos")

Step 2: Set up your go.mod and go.sum

The generated Go code requires google.golang.org/protobuf to compile. Add it to your go.mod with the version you'd like. Then run go mod download all to update your go.sum.

go.mod

require google.golang.org/protobuf v1.27.1

Step 3: Add option go_package to .proto files

Every Protobuf file that should work with Go must set option go_package with the name of its Go package. For example:

src/protos/example/v1/person.proto

syntax = "proto3";

package simple_example.v1;

option go_package = "github.com/pantsbuild/example-codegen/gen";

Multiple Protobuf files can set the same go_package if their code should show up in the same package.

Step 4: Generate protobuf_sources targets

Run pants tailor :: for Pants to create a protobuf_sources target wherever you have .proto files:

❯ pants tailor ::
Created src/protos/BUILD:
  - Add protobuf_sources target protos

Pants will use dependency inference for any import statements in your .proto files, which you can confirm by running pants dependencies path/to/file.proto.

If you want gRPC code generated for all files in the folder, set grpc=True.

src/proto/example/BUILD

protobuf_sources(
    name="protos",
    grpc=True,
)

If you only want gRPC generated for some files in the folder, you can use the overrides field:

src/proto/example/BUILD

protobuf_sources(
    name="protos",
    overrides={
        "admin.proto": {"grpc": True},
        # You can also use a tuple for multiple files.
        ("user.proto", "org.proto"): {"grpc": True},
    },
)

Step 5: Confirm Go imports are working

Now, you can import the generated Go package in your Go code like normal, using whatever you set with option go_package from Step 3.

src/go/examples/proto_test.go

package examples

import "testing"
import "github.com/pantsbuild/example-codegen/gen"

func TestGenerateUuid(t *testing.T) {
	person := gen.Person{
		Name:  "Thomas the Train",
		Id:    1,
		Email: "[email protected]",
	}
	if person.Name != "Thomas the Train" {
		t.Fail()
	}
}

Pants's dependency inference will detect Go imports of Protobuf packages, which you can confirm by running pants dependencies path/to/file.go. You can also run pants check path/to/file.go to confirm that everything compiles.

Run pants export-codegen :: to inspect the files

pants export-codegen :: will run all relevant code generators and write the files to dist/codegen using the same paths used normally by Pants.

You do not need to run this goal for codegen to work when using Pants; export-codegen is only for external consumption outside of Pants, e.g. to get go mod tidy working.

Buf: format and lint Protobuf

Pants integrates with the Buf formatter and linter for Protobuf files.

To activate, add this to pants.toml:

pants.toml

[GLOBAL]
backend_packages = [
  "pants.backend.codegen.protobuf.lint.buf",
]

Now you can run pants fmt and pants lint:

❯ pants lint src/protos/user.proto

Use pants fmt lint dir: to run on all files in the directory, and pants fmt lint dir:: to run on all files in the directory and subdirectories.

Temporarily disable Buf with --buf-fmt-skip and --buf-lint-skip:

❯ pants --buf-fmt-skip fmt ::

Only run Buf with --lint-only=buf-fmt or --lint-only=buf-lint, and --fmt-only=buf-fmt:

❯ pants fmt --only=buf-fmt ::