Add support for Rails 5 API-only applications (#793)

lib/draper.rb

@@ -11,6 +11,7 @@ require 'active_support/core_ext/name_error'
 require 'draper/version'
 require 'draper/configuration'
 require 'draper/view_helpers'
+require 'draper/compatibility/api_only'
 require 'draper/delegation'
 require 'draper/automatic_delegation'
 require 'draper/finders'
@@ -32,6 +33,7 @@ module Draper
 
   def self.setup_action_controller(base)
     base.class_eval do
+      include Draper::Compatibility::ApiOnly if base == ActionController::API
       include Draper::ViewContext
       extend  Draper::HelperSupport
       extend  Draper::DecoratesAssigned

lib/draper/compatibility/api_only.rb

@@ -0,0 +1,23 @@
+module Draper
+  module Compatibility
+    # Draper expects your `ApplicationController` to include `ActionView::Rendering`. The
+    # `ApplicationController` generated by Rails 5 API-only applications (created with
+    # `rails new --api`) don't by default. However, including `ActionView::Rendering` in
+    # `ApplicatonController` breaks `render :json` due to `render_to_body` being overridden.
+    #
+    # This compatibility patch fixes the issue by restoring the original `render_to_body`
+    # method after including `ActionView::Rendering`. Ultimately, including `ActionView::Rendering`
+    # in an ActionController::API may not be supported functionality by Rails (see Rails issue
+    # for more detail: https://github.com/rails/rails/issues/27211). This hack is meant to be a
+    # temporary solution until we can find a way to not rely on the controller layer.
+    module ApiOnly
+      extend ActiveSupport::Concern
+
+      included do
+        alias :previous_render_to_body :render_to_body
+        include ActionView::Rendering
+        alias :render_to_body :previous_render_to_body
+      end
+    end
+  end
+end

spec/draper/draper_spec.rb

@@ -0,0 +1,24 @@
+require 'spec_helper'
+require 'support/shared_examples/view_helpers'
+
+module Draper
+  describe Draper do
+    describe '.setup_action_controller' do
+      it 'includes api only compatability if base is ActionController::API' do
+        base = ActionController::API
+
+        Draper.setup_action_controller(base)
+
+        expect(base.included_modules).to include(Draper::Compatibility::ApiOnly)
+      end
+
+      it 'does not include api only compatibility if base ActionController::Base' do
+        base = ActionController::Base
+
+        Draper.setup_action_controller(base)
+
+        expect(base.included_modules).not_to include(Draper::Compatibility::ApiOnly)
+      end
+    end
+  end
+end