If partial is rendered in controller, grab format from template

Previously `rendered_format` was set only based on mime types
passed in Accept header, which was wrong if first type from
Accept was different than rendered partial. The fix is to simply
move setting rendered_format to the place where template
is available and grab format from the template. If it fails
we can fallback to formats passed by Accept header.

actionpack/lib/action_view/renderer/partial_renderer.rb

@@ -257,6 +257,14 @@ module ActionView
       setup(context, options, block)
       identifier = (@template = find_partial) ? @template.identifier : @path
 
+      @lookup_context.rendered_format ||= begin
+        if @template && @template.formats.present?
+          @template.formats.first
+        else
+          formats.first
+        end
+      end
+
       if @collection
         instrument(:collection, :identifier => identifier || "collection", :count => @collection.size) do
           render_collection
@@ -316,8 +324,6 @@ module ActionView
       @block   = block
       @details = extract_details(options)
 
-      @lookup_context.rendered_format ||= formats.first
-
       if String === partial
         @object     = options[:object]
         @path       = partial

actionpack/test/controller/render_test.rb

@@ -553,6 +553,10 @@ class TestController < ActionController::Base
     render :partial => 'partial'
   end
 
+  def partial_html_erb
+    render :partial => 'partial_html_erb'
+  end
+
   def render_to_string_with_partial
     @partial_only = render_to_string :partial => "partial_only"
     @partial_with_locals = render_to_string :partial => "customer", :locals => { :customer => Customer.new("david") }
@@ -1272,6 +1276,15 @@ class RenderTest < ActionController::TestCase
     assert_equal "text/html", @response.content_type
   end
 
+  def test_render_html_formatted_partial_even_with_other_mime_time_in_accept
+    @request.accept = "text/javascript, text/html"
+
+    get :partial_html_erb
+
+    assert_equal "partial.html.erb", @response.body.strip
+    assert_equal "text/html", @response.content_type
+  end
+
   def test_should_render_html_partial_with_formats
     get :partial_formats_html
     assert_equal "partial html", @response.body

actionpack/test/fixtures/test/_partial_html_erb.html.erb

@@ -0,0 +1 @@
+<%= "partial.html.erb" %>