Generating Protobuf from Bosatsu Values

Bosatsu supports protobuf value generation through a standard protoc plugin: protoc-gen-bosatsu.

The plugin generates Bosatsu struct/enum models from .proto files and also emits per-message codec functions:

• encode_<Message>: <Message> -> Bosatsu/IO/Bytes::Bytes
• decode_<Message>: Bosatsu/IO/Bytes::Bytes -> Option[<Message>]

The generated codecs use Bosatsu/Proto/Wire, so they run in JVM eval, Python transpile, and C transpile flows without linking protobuf runtime libraries in those targets.

Quick Start

1. Build the CLI assembly:

sbt cli/assembly

1. Run protoc with the Bosatsu plugin:

PATH="$PWD:$PATH" protoc \
  --plugin=protoc-gen-bosatsu="$PWD/protoc-gen-bosatsu" \
  --bosatsu_out=. \
  --proto_path=. \
  core/src/test/resources/protobuf/config_v1.proto

The protoc-gen-bosatsu wrapper invokes the main CLI plugin command:

./bosatsu tool protoc-plugin

The same plugin subcommand is also available from the Node CLI build:

./bosatsu_node tool protoc-plugin

This writes a Bosatsu package under Proto/... that corresponds to the protobuf package (for example config.v1 -> Proto/Config/V1).

1. Typecheck your workspace:

./bosatsuj lib check --name core_alpha

1. Use generated codecs in Bosatsu:

from Bosatsu/IO/Bytes import to_List_Int
from Proto/Config/V1 import AppConfig, encode_AppConfig, decode_AppConfig

encoded = encode_AppConfig(AppConfig {
  name: "api",
  replicas: 3,
  weights: [-1, 0, 7],
  mode: Mode_ModeActive,
  transport: AppConfig_Transport_NotSet,
  ratio: 0.5,
  epsilon: 1.25,
  labels: [("env", "prod")],
})

roundtrip_ok =
  match decode_AppConfig(encoded):
    case Some(value): encode_AppConfig(value) == encoded
    case None: False

Notes

• Phase 1 supports proto3 only.
• Unknown fields are skipped while decoding.
• Map fields are represented as List[(K, V)] in generated Bosatsu.
• Both protobuf float and double map to Bosatsu Float64 in generated APIs.