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.

• 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.
• RBS_PROTOBUF_ACCEPT_NIL_ATTR_WRITER is to allow passing nil to required fields.
• RBS_PROTOBUF_FILTERS contains filter Ruby script paths separated by File::PATH_SEPARATOR
• RBS_PROTOBUF_CONCAT_LEVEL contains the number of dir levels that groups generated RBS files to concat

To type check the output, make sure your type checker configuration loads type definitions of protobuf gem.

# Declare in Gemfile and load it with rbs-collection
gem '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.

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.

You can apply filters that modifies generated RBS files.

A filter is a proc object with type of ^(String rbs_name, String rbs_content, untyped proto_file) -> [String, String]: It receives the file name of RBS file, the content of RBS file, the source protobuf object, and returns a pair of RBS file name and content.

# example_fitler.rb: It adds a warning comment at the top of the RBS content.
->(rbs_name, rbs_content, _proto_file) {
  [
    rbs_name,
    "# Don't modify this file. This is generated with rbs_protobuf.\n\n" + rbs_content
  ]
}

You can apply filters by setting RBS_PROTOBUF_FILTERS environment variable.

$ RBS_PROTOBUF_BACKEND=protobuf RBS_PROTOBUF_FILTERS=example_filter.rb protoc ...

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.