Fail informatively in #respond_with when no appropriate #api_behavior renderer is available.

Currently if a user calls #respond_with(csvable), but has not csv
renderer available, Responder will just run through the default render
behavior twice, raising ActionView::MissingTemplate both times.

This changes ActionController::Metal::Responder#api_behavior to check
in advance whether there is a renderer available, and raise
ActionController::MissingRenderer if not.

2 files changed, 13 insertions, 0 deletions

diff --git a/actionpack/lib/action_controller/metal/renderers.rb b/actionpack/lib/action_controller/metal/renderers.rb
index 5272dc6cdb..abed6e53cc 100644
--- a/actionpack/lib/action_controller/metal/renderers.rb
+++ b/actionpack/lib/action_controller/metal/renderers.rb
@@ -6,6 +6,13 @@ module ActionController
     Renderers.add(key, &block)
   end
 
+  class MissingRenderer < LoadError
+    def initialize(format)
+      @format = format
+      super("No renderer defined for format: #{@format}")
+    end
+  end
+
   module Renderers
     extend ActiveSupport::Concern
 
diff --git a/actionpack/lib/action_controller/metal/responder.rb b/actionpack/lib/action_controller/metal/responder.rb
index fd5b661209..66ff34a794 100644
--- a/actionpack/lib/action_controller/metal/responder.rb
+++ b/actionpack/lib/action_controller/metal/responder.rb
@@ -202,6 +202,7 @@ module ActionController #:nodoc:
     # This is the common behavior for formats associated with APIs, such as :xml and :json.
     def api_behavior(error)
       raise error unless resourceful?
+      raise MissingRenderer.new(format) unless has_renderer?
 
       if get?
         display resource
@@ -269,6 +270,11 @@ module ActionController #:nodoc:
       resource.respond_to?(:errors) && !resource.errors.empty?
     end
 
+    # Check whether the neceessary Renderer is available
+    def has_renderer?
+      Renderers::RENDERERS.include?(format)
+    end
+
     # By default, render the <code>:edit</code> action for HTML requests with errors, unless
     # the verb was POST.
     #