2 files changed, 15 insertions, 1 deletions
diff --git a/actionpack/lib/abstract_controller/collector.rb b/actionpack/lib/abstract_controller/collector.rb
index 09b9e7ddf0..ddd56b354a 100644
--- a/actionpack/lib/abstract_controller/collector.rb
+++ b/actionpack/lib/abstract_controller/collector.rb
@@ -23,7 +23,17 @@ module AbstractController
   protected
 
     def method_missing(symbol, &block)
-      mime_constant = Mime.const_get(symbol.upcase)
+      const_name = symbol.upcase
+
+      unless Mime.const_defined?(const_name)
+        raise NoMethodError, "To respond to a custom format, register it as a MIME type first: " \
+          "http://guides.rubyonrails.org/action_controller_overview.html#restful-downloads. " \
+          "If you meant to respond to a variant like :tablet or :phone, not a custom format, " \
+          "be sure to nest your variant response within a format response: " \
+          "format.html { |html| html.tablet { ... } }"
+      end
+
+      mime_constant = Mime.const_get(const_name)
 
       if Mime::SET.include?(mime_constant)
         AbstractController::Collector.generate_method_for_mime(mime_constant)
diff --git a/actionpack/lib/abstract_controller/rendering.rb b/actionpack/lib/abstract_controller/rendering.rb
index a6e230a088..6f17e3fcd9 100644
--- a/actionpack/lib/abstract_controller/rendering.rb
+++ b/actionpack/lib/abstract_controller/rendering.rb
@@ -1,5 +1,6 @@
 require 'active_support/concern'
 require 'active_support/core_ext/class/attribute'
+require 'action_view/view_paths'
 require 'set'
 
 module AbstractController
@@ -13,6 +14,7 @@ module AbstractController
 
   module Rendering
     extend ActiveSupport::Concern
+    include ActionView::ViewPaths
 
     # Normalize arguments, options and then delegates render_to_body and
     # sticks the result in self.response_body.
@@ -102,6 +104,8 @@ module AbstractController
     # :api: private
     def _normalize_render(*args, &block)
       options = _normalize_args(*args, &block)
+      #TODO: remove defined? when we restore AP <=> AV dependency
+      options[:variant] = request.variant if defined?(request) && request.variant.present?
       _normalize_options(options)
       options
     end