Implementing Routing Concerns

This pattern was introduced as a plugin by @dhh.

The original implementation can be found in
https://github.com/rails/routing_concerns

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -909,7 +909,7 @@ module Resources
        # CANONICAL_ACTIONS holds all actions that does not need a prefix or
        # a path appended since they fit properly in their scope level.
        VALID_ON_OPTIONS  = [:new, :collection, :member]
        RESOURCE_OPTIONS  = [:as, :controller, :path, :only, :except, :param]
        RESOURCE_OPTIONS  = [:as, :controller, :path, :only, :except, :param, :concerns]
        CANONICAL_ACTIONS = %w(index create new show update destroy)

        class Resource #:nodoc:
@@ -1046,6 +1046,8 @@ def resource(*resources, &block)
          resource_scope(:resource, SingletonResource.new(resources.pop, options)) do
            yield if block_given?

            concerns(options[:concerns]) if options[:concerns]

            collection do
              post :create
            end if parent_resource.actions.include?(:create)
@@ -1210,6 +1212,8 @@ def resources(*resources, &block)
          resource_scope(:resources, Resource.new(resources.pop, options)) do
            yield if block_given?

            concerns(options[:concerns]) if options[:concerns]

            collection do
              get  :index if parent_resource.actions.include?(:index)
              post :create if parent_resource.actions.include?(:create)
@@ -1580,15 +1584,33 @@ def name_for_action(as, action) #:nodoc:
          end
      end

      module Concerns
        def concern(name, &block)
          @concerns[name] = block
        end

        def concerns(*names)
          names.flatten.each do |name|
            if concern = @concerns[name]
              instance_eval(&concern)
            else
              raise ArgumentError, "No concern named #{name} was found!"
            end
          end
        end
      end

      def initialize(set) #:nodoc:
        @set = set
        @scope = { :path_names => @set.resources_path_names }
        @concerns = {}
      end

      include Base
      include HttpHelpers
      include Redirection
      include Scoping
      include Concerns
      include Resources
    end
  end

actionpack/test/dispatch/routing/concerns_test.rb

@@ -0,0 +1,94 @@
require 'abstract_unit'

class CommentsController < ActionController::Base
  def index
    head :ok
  end
end

class ImageAttachmentsController < ActionController::Base
  def index
    head :ok
  end
end

class RoutingConcernsTest < ActionDispatch::IntegrationTest
  Routes = ActionDispatch::Routing::RouteSet.new.tap do |app|
    app.draw do
      concern :commentable do
        resources :comments
      end

      concern :image_attachable do
        resources :image_attachments, only: :index
      end

      resources :posts, concerns: [:commentable, :image_attachable] do
        resource :video, concerns: :commentable
      end

      resource :picture, concerns: :commentable do
        resources :posts, concerns: :commentable
      end

      scope "/videos" do
        concerns :commentable
      end
    end
  end

  include Routes.url_helpers
  def app; Routes end

  def test_accessing_concern_from_resources
    get "/posts/1/comments"
    assert_equal "200", @response.code
    assert_equal "/posts/1/comments", post_comments_path(post_id: 1)
  end

  def test_accessing_concern_from_resource
    get "/picture/comments"
    assert_equal "200", @response.code
    assert_equal "/picture/comments", picture_comments_path
  end

  def test_accessing_concern_from_nested_resource
    get "/posts/1/video/comments"
    assert_equal "200", @response.code
    assert_equal "/posts/1/video/comments", post_video_comments_path(post_id: 1)
  end

  def test_accessing_concern_from_nested_resources
    get "/picture/posts/1/comments"
    assert_equal "200", @response.code
    assert_equal "/picture/posts/1/comments", picture_post_comments_path(post_id: 1)
  end

  def test_accessing_concern_from_resources_with_more_than_one_concern
    get "/posts/1/image_attachments"
    assert_equal "200", @response.code
    assert_equal "/posts/1/image_attachments", post_image_attachments_path(post_id: 1)
  end

  def test_accessing_concern_from_resources_using_only_option
    get "/posts/1/image_attachment/1"
    assert_equal "404", @response.code
  end

  def test_accessing_concern_from_a_scope
    get "/videos/comments"
    assert_equal "200", @response.code
  end

  def test_with_an_invalid_concern_name
    e = assert_raise ArgumentError do
      ActionDispatch::Routing::RouteSet.new.tap do |app|
        app.draw do
          resources :posts, concerns: :foo
        end
      end
    end

    assert_equal "No concern named foo was found!", e.message
  end
end