Don't call additional methods on builders passed to the atom_feed helper.

Additionally, actually test that the atom_feed helper works with :xml as an option.

[#1836 state:committed]

actionpack/lib/action_view/helpers/atom_feed_helper.rb

@@ -98,7 +98,7 @@ module ActionView
           options[:schema_date] = "2005" # The Atom spec copyright date
         end
 
-        xml = options[:xml] || eval("xml", block.binding)
+        xml = options.delete(:xml) || eval("xml", block.binding)
         xml.instruct!
         if options[:instruct]
           options[:instruct].each do |target,attrs|

actionpack/test/template/atom_feed_helper_test.rb

@@ -157,6 +157,26 @@ class ScrollsController < ActionController::Base
           end
         end
     EOT
+    FEEDS["provide_builder"] = <<-'EOT'
+          # we pass in the new_xml to the helper so it doesn't
+          # call anything on the original builder
+          new_xml = Builder::XmlMarkup.new(:target=>'')
+          atom_feed(:xml => new_xml) do |feed|
+            feed.title("My great blog!")
+            feed.updated((@scrolls.first.created_at))
+
+            for scroll in @scrolls
+              feed.entry(scroll) do |entry|
+                entry.title(scroll.title)
+                entry.content(scroll.body, :type => 'html')
+
+                entry.author do |author|
+                  author.name("DHH")
+                end
+              end
+            end
+          end
+    EOT
   def index
     @scrolls = [
       Scroll.new(1, "1", "Hello One", "Something <i>COOL!</i>", Time.utc(2007, 12, 12, 15), Time.utc(2007, 12, 12, 15)),
@@ -202,6 +222,15 @@ class AtomFeedTest < ActionController::TestCase
     end
   end
 
+  def test_providing_builder_to_atom_feed
+    with_restful_routing(:scrolls) do
+      get :index, :id=>"provide_builder"
+      # because we pass in the non-default builder, the content generated by the
+      # helper should go 'nowhere'.  Leaving the response body blank.
+      assert @response.body.blank?
+    end
+  end
+
   def test_entry_with_prefilled_options_should_use_those_instead_of_querying_the_record
     with_restful_routing(:scrolls) do
       get :index, :id => "entry_options"