Action Pack Variants

By default, variants in the templates will be picked up if a variant is set
and there's a match. The format will be:

  app/views/projects/show.html.erb
  app/views/projects/show.html+tablet.erb
  app/views/projects/show.html+phone.erb

If request.variant = :tablet is set, we'll automatically be rendering the
html+tablet template.

In the controller, we can also tailer to the variants with this syntax:

  class ProjectsController < ActionController::Base
    def show
      respond_to do |format|
        format.html do |html|
          @stars = @project.stars

          html.tablet { @notifications = @project.notifications }
          html.phone  { @chat_heads    = @project.chat_heads }
        end

        format.js
        format.atom
      end
    end
  end

The variant itself is nil by default, but can be set in before filters, like
so:

  class ApplicationController < ActionController::Base
    before_action do
      if request.user_agent =~ /iPad/
        request.variant = :tablet
      end
    end
  end

This is modeled loosely on custom mime types, but it's specifically not
intended to be used together. If you're going to make a custom mime type,
you don't need a variant. Variants are for variations on a single mime
types.

2 files changed, 11 insertions, 1 deletions

diff --git a/actionpack/lib/abstract_controller/collector.rb b/actionpack/lib/abstract_controller/collector.rb
index 09b9e7ddf0..f7a309c26c 100644
--- a/actionpack/lib/abstract_controller/collector.rb
+++ b/actionpack/lib/abstract_controller/collector.rb
@@ -23,7 +23,15 @@ module AbstractController
   protected
 
     def method_missing(symbol, &block)
-      mime_constant = Mime.const_get(symbol.upcase)
+      mime_const = symbol.upcase
+
+      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 { ..." unless Mime.const_defined?(mime_const)
+
+      mime_constant = Mime.const_get(mime_const)
 
       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 fb8f40cb9b..ce3a0316c4 100644
--- a/actionpack/lib/abstract_controller/rendering.rb
+++ b/actionpack/lib/abstract_controller/rendering.rb
@@ -102,6 +102,8 @@ 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