rbs_protobuf is a RBS generator for Protocol Buffer messages. It parses .proto files and generates RBS type signature.

It works as a protoc plugin and generates RBSs for protobuf gem. (We plan to support google-protobuf gem too.)

This is an example .proto file.

syntax = "proto2";

package protobuf.example;

message SearchRequest {
  required string query = 1;
  optional int32 page_number = 2;
  optional int32 result_per_page = 3;
}

rbs_protobuf will generate the following RBS file including method definitions for each attribute with correct types.

module Protobuf
  module Example
    class SearchRequest < ::Protobuf::Message
      attr_reader query(): ::String

      attr_writer query(): ::String?

      attr_reader page_number(): ::Integer

      attr_writer page_number(): ::Integer?

      attr_reader result_per_page(): ::Integer

      attr_writer result_per_page(): ::Integer?

      def initialize: (?query: ::String?, ?page_number: ::Integer?, ?result_per_page: ::Integer?) -> void

      def []: (:query) -> ::String
            | (:page_number) -> ::Integer
            | (:result_per_page) -> ::Integer
            | (::Symbol) -> untyped

      def []=: (:query, ::String?) -> ::String?
             | (:page_number, ::Integer?) -> ::Integer?
             | (:result_per_page, ::Integer?) -> ::Integer?
             | (::Symbol, untyped) -> untyped
    end
  end
end

And you can type check your Ruby program using the classes with RBS above. 💪

Add this line to your application's Gemfile:

group :development do
  gem 'rbs_protobuf', require: false
end

And then execute:

$ bundle install

Or install it yourself as:

$ gem install rbs_protobuf

Run protoc with --rbs_out option.

$ RBS_PROTOBUF_BACKEND=protobuf protoc --rbs_out=sig/protos protos/a.proto

You may need bundle exec protoc ... to let bundler set up PATH.

To type check the output, you need to configure your tools to import gem_rbs_collection with rbs collection command.

# Add the dependency in rbs_collection.yaml
gems:
  - name: rbs_protobuf

We assume that you don't type check the generated .pb.rb code. If you want to type check them, you need the definition of Google::Protobuf, which can be generated from descriptor.proto.

• RBS_PROTOBUF_BACKEND specifies the Ruby code generator gem. Supported value is protobuf. (We will add google-protobuf for google-protobuf gem.)
• PB_UPCASE_ENUMS is for protobuf gem support. Specify the environment variable to make enum value constants upper case.
• RBS_PROTOBUF_NO_NESTED_NAMESPACE is to make the RBS declarations flat.
• RBS_PROTOBUF_EXTENSION specifies what to do for extensions.

Adding extensions may cause problems if the name of new attribute conflicts.

extend SearchRequest {
  // This extension defines an attribute.
  optional string option = 100;
}

extend SearchRequest {
  // Another extension defines another attribute with same name.
  optional string option = 101;
}

In this case, defining two option attributes in RBS causes an error. So, rbs_protobuf allows ignoring extensions for this case.

You can control the behavior with RBS_PROTOBUF_EXTENSION environment variable.

• false: Ignores extensions.
• print: Prints RBS for extensions instead of writing them to files. You can copy or modify the printed RBS, and put them in some RBS files.
• Any value else: Generates RBS for extensions.
• undefined: Ignores extensions but print messages to ask you to specify a value.

After checking out the repo, run bin/setup to install dependencies. Then, run rake test example:typecheck to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

The gem works as a plugin of protoc command, so protoc command should be available for development.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/square/rbs_protobuf.

The gem is available as open source under the terms of the MIT License.