1 files changed, 17 insertions, 2 deletions
diff --git a/actionpack/lib/action_controller/routing.rb b/actionpack/lib/action_controller/routing.rb
index 5b888443d8..58207eed74 100644
--- a/actionpack/lib/action_controller/routing.rb
+++ b/actionpack/lib/action_controller/routing.rb
@@ -1240,8 +1240,11 @@ module ActionController
 
         if named_route
           path = named_route.generate(options, merged, expire_on)
-          raise RoutingError, "#{named_route_name}_url failed to generate from #{options.inspect}, expected: #{named_route.requirements.inspect}, diff: #{named_route.requirements.diff(options).inspect}" if path.nil?
-          return path
+          if path.nil? 
+            raise_named_route_error(options, named_route, named_route_name)
+          else
+            return path
+          end
         else
           merged[:action] ||= 'index'
           options[:action] ||= 'index'
@@ -1269,6 +1272,18 @@ module ActionController
     
         raise RoutingError, "No route matches #{options.inspect}"
       end
+      
+      # try to give a helpful error message when named route generation fails
+      def raise_named_route_error(options, named_route, named_route_name)
+        diff = named_route.requirements.diff(options)
+        unless diff.empty?
+          raise RoutingError, "#{named_route_name}_url failed to generate from #{options.inspect}, expected: #{named_route.requirements.inspect}, diff: #{named_route.requirements.diff(options).inspect}"
+        else
+          required_segments = named_route.segments.select {|seg| (!seg.optional?) && (!seg.is_a?(DividerSegment)) }
+          required_keys_or_values = required_segments.map { |seg| seg.key rescue seg.value } # we want either the key or the value from the segment
+          raise RoutingError, "#{named_route_name}_url failed to generate from #{options.inspect} - you may have ambiguous routes, or you may need to supply additional parameters for this route.  content_url has the following required parameters: #{required_keys_or_values.inspect} - are they all satisifed?"
+        end
+      end
   
       def recognize(request)
         params = recognize_path(request.path, extract_request_environment(request))