1 files changed, 16 insertions, 2 deletions
diff --git a/actionpack/lib/action_controller/abstract/renderer.rb b/actionpack/lib/action_controller/abstract/renderer.rb
index beb848f90e..b58688c9da 100644
--- a/actionpack/lib/action_controller/abstract/renderer.rb
+++ b/actionpack/lib/action_controller/abstract/renderer.rb
@@ -1,6 +1,15 @@
 require "action_controller/abstract/logger"
 
 module AbstractController
+  class AbstractControllerError < StandardError; end
+  class DoubleRenderError < AbstractControllerError
+    DEFAULT_MESSAGE = "Render and/or redirect were called multiple times in this action. Please note that you may only call render OR redirect, and at most once per action. Also note that neither redirect nor render terminate execution of the action, so if you want to exit an action after redirecting, you need to do something like \"redirect_to(...) and return\"."
+
+    def initialize(message = nil)
+      super(message || DEFAULT_MESSAGE)
+    end
+  end  
+  
   module Renderer
     extend ActiveSupport::DependencyModule
 
@@ -19,6 +28,10 @@ module AbstractController
     end
         
     def render(options = {})
+      if response_body
+        raise AbstractController::DoubleRenderError, "OMG"
+      end
+      
       self.response_body = render_to_body(options)
     end
     
@@ -31,8 +44,9 @@ module AbstractController
     def render_to_body(options = {})
       name = options[:_template_name] || action_name
       
-      template = options[:_template] || view_paths.find_by_parts(name.to_s, {:formats => formats}, options[:_prefix])
-      _render_template(template, options)
+      options[:_template] ||= view_paths.find_by_parts(name.to_s, {:formats => formats}, options[:_prefix])
+      
+      _render_template(options[:_template], options)
     end
 
     # Raw rendering of a template to a string.