Add RBS files for sinatra and sinatra-contrib gems (#561)

Generated initial RBS files using the `rbs prototype rb` command,
and added type definitions for both the Sinatra core and contributed extensions.

https://github.com/sinatra/sinatra/tree/v4.0.0

I have set myself as the reviewer for this change because I believe
the sinatra gem is an important and widely-used web framework.
However, I am not very familiar with sinatra, so if there is someone who
uses sinatra regularly and is motivated to maintain these type definitions,
I would appreciate it if they could take over the reviewer role.

gems/sinatra-contrib/4.0/json.rbs

@@ -0,0 +1,103 @@
+module Sinatra
+  # = Sinatra::JSON
+  #
+  # <tt>Sinatra::JSON</tt> adds a helper method, called +json+, for (obviously)
+  # json generation.
+  #
+  # == Usage
+  #
+  # === Classic Application
+  #
+  # In a classic application simply require the helper, and start using it:
+  #
+  #     require "sinatra"
+  #     require "sinatra/json"
+  #
+  #     # define a route that uses the helper
+  #     get '/' do
+  #       json :foo => 'bar'
+  #     end
+  #
+  #     # The rest of your classic application code goes here...
+  #
+  # === Modular Application
+  #
+  # In a modular application you need to require the helper, and then tell the
+  # application you will use it:
+  #
+  #     require "sinatra/base"
+  #     require "sinatra/json"
+  #
+  #     class MyApp < Sinatra::Base
+  #
+  #       # define a route that uses the helper
+  #       get '/' do
+  #         json :foo => 'bar'
+  #       end
+  #
+  #       # The rest of your modular application code goes here...
+  #     end
+  #
+  # === Encoders
+  #
+  # By default it will try to call +to_json+ on the object, but if it doesn't
+  # respond to that message, it will use its own rather simple encoder.  You can
+  # easily change that anyways. To use +JSON+, simply require it:
+  #
+  #   require 'json'
+  #
+  # The same goes for <tt>Yajl::Encoder</tt>:
+  #
+  #   require 'yajl'
+  #
+  # For other encoders, besides requiring them, you need to define the
+  # <tt>:json_encoder</tt> setting.  For instance, for the +Whatever+ encoder:
+  #
+  #   require 'whatever'
+  #   set :json_encoder, Whatever
+  #
+  # To force +json+ to simply call +to_json+ on the object:
+  #
+  #   set :json_encoder, :to_json
+  #
+  # Actually, it can call any method:
+  #
+  #   set :json_encoder, :my_fancy_json_method
+  #
+  # === Content-Type
+  #
+  # It will automatically set the content type to "application/json".  As
+  # usual, you can easily change that, with the <tt>:json_content_type</tt>
+  # setting:
+  #
+  #   set :json_content_type, :js
+  #
+  # === Overriding the Encoder and the Content-Type
+  #
+  # The +json+ helper will also take two options <tt>:encoder</tt> and
+  # <tt>:content_type</tt>.  The values of this options are the same as the
+  # <tt>:json_encoder</tt> and <tt>:json_content_type</tt> settings,
+  # respectively.  You can also pass those to the json method:
+  #
+  #   get '/'  do
+  #     json({:foo => 'bar'}, :encoder => :to_json, :content_type => :js)
+  #   end
+  #
+  module JSON
+    def self.encode: (untyped object) -> untyped
+
+    def json: (Hash[untyped, untyped] object, ?::Hash[untyped, untyped] options) -> untyped
+
+    private
+
+    def resolve_content_type: (?::Hash[untyped, untyped] options) -> untyped
+
+    def resolve_encoder: (?::Hash[untyped, untyped] options) -> untyped
+
+    def resolve_encoder_action: (untyped object, untyped encoder) -> untyped
+  end
+
+  class Base
+    extend JSON
+  end
+end

gems/sinatra-contrib/_reviewers.yaml

@@ -0,0 +1,2 @@
+reviewers:
+  - euglena1215

gems/sinatra/4.0/_test/metadata.yaml

@@ -0,0 +1,2 @@
+additional_gems:
+  - sinatra-contrib

gems/sinatra/4.0/_test/test.rb

@@ -0,0 +1,45 @@
+require "sinatra/base"
+require "sinatra/json"
+
+class MyApp < Sinatra::Base
+  enable :logging
+  set :sessions, domain: 'example.dev', path: '/', expire_after: 1000*60
+
+  class HttpError < StandardError
+    # @dynamic code
+    attr_reader :code
+
+    def initialize(code)
+      super("HTTP error #{code}")
+      @code = code
+    end
+  end
+
+  error HttpError do
+    status 400
+    json(error: 'HTTP error')
+  end
+
+  # @dynamic self.foo, self.bar
+  helpers do
+    def foo
+      'foo'
+    end
+
+    def bar
+      foo
+    end
+  end
+
+  get '/' do
+    json(foo: foo, bar: bar)
+  end
+
+  post '/' do
+    json(foo: foo, bar: bar)
+  end
+
+  patch '/' do
+    raise HttpError.new(401)
+  end
+end

gems/sinatra/4.0/_test/test.rbs

@@ -0,0 +1,15 @@
+class MyApp < Sinatra::Base
+  # Methods defined in the helpers block must be recognized as instance
+  # methods for method calls from within other helper blocks, and as
+  # singleton methods for calls from HTTP verbs (get, post, patch, etc.).
+  def self.foo: () -> String
+  def foo: () -> String
+  def self.bar: () -> String
+  def bar: () -> String
+
+  class HttpError < StandardError
+    attr_reader code: Integer
+
+    def initialize: (Integer) -> void
+  end
+end