6 files changed, 45 insertions, 0 deletions
diff --git a/actionpack/CHANGELOG b/actionpack/CHANGELOG
index e89123e679..bc8caaa3ef 100644
--- a/actionpack/CHANGELOG
+++ b/actionpack/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Make render :partial recognise form builders and use the _form partial.  #10814 [djanowski]
+
 * Allow users to declare other namespaces when using the atom feed helpers. #10304 [david.calavera]
 
 * Introduce send_file :x_sendfile => true to send an X-Sendfile response header.  [Jeremy Kemper]
diff --git a/actionpack/lib/action_view/helpers/form_helper.rb b/actionpack/lib/action_view/helpers/form_helper.rb
index f67a040149..d2835a2438 100644
--- a/actionpack/lib/action_view/helpers/form_helper.rb
+++ b/actionpack/lib/action_view/helpers/form_helper.rb
@@ -32,6 +32,15 @@ module ActionView
     #       <input name="commit" type="submit" value="Create" />
     #     </form>
     #
+    # If you are using a partial for your form fields, you can use this shortcut:
+    #
+    #     <% form_for :person, @person, :url => { :action => "create" } do |f| %>
+    #       <%= render :partial => f %>
+    #       <%= submit_tag 'Create' %>
+    #     <% end %>
+    #
+    # This example will render the <tt>people/_form</tt> partial, setting a local variable called <tt>form</tt> which references the yielded FormBuilder.
+    #
     # The <tt>params</tt> object created when this form is submitted would look like:
     #
     #     {"action"=>"create", "controller"=>"persons", "person"=>{"first_name"=>"William", "last_name"=>"Smith"}}
@@ -153,6 +162,12 @@ module ActionView
       #     <%= check_box_tag "person[admin]", @person.company.admin? %>
       #   <% end %>
       #
+      # In this case, if you use this:
+      #
+      #   <%= render :partial => f %>
+      #
+      # The rendered template is <tt>people/_labelling_form</tt> and the local variable referencing the form builder is called <tt>labelling_form</tt>.
+      #
       # In many cases you will want to wrap the above in another helper, so you could do something like the following:
       #
       #   def labelled_form_for(record_or_name_or_array, *args, &proc)
diff --git a/actionpack/lib/action_view/partials.rb b/actionpack/lib/action_view/partials.rb
index 0795b8ec55..a1ba60d560 100644
--- a/actionpack/lib/action_view/partials.rb
+++ b/actionpack/lib/action_view/partials.rb
@@ -119,6 +119,9 @@ module ActionView
           else
             render("#{path}/_#{partial_name}", local_assigns)
           end
+        when ActionView::Helpers::FormBuilder
+          builder_partial_path = partial_path.class.to_s.demodulize.underscore.sub(/_builder$/, '')
+          render_partial(builder_partial_path, object_assigns, (local_assigns || {}).merge(builder_partial_path.to_sym => partial_path))
         when Array, ActiveRecord::Associations::AssociationCollection, ActiveRecord::Associations::HasManyThroughAssociation
           if partial_path.any?
             path       = ActionController::RecordIdentifier.partial_path(partial_path.first)
diff --git a/actionpack/test/controller/new_render_test.rb b/actionpack/test/controller/new_render_test.rb
index e06737ee0b..eb19b2e391 100644
--- a/actionpack/test/controller/new_render_test.rb
+++ b/actionpack/test/controller/new_render_test.rb
@@ -17,6 +17,9 @@ module NewRenderTestHelper
   end
 end
 
+class LabellingFormBuilder < ActionView::Helpers::FormBuilder
+end
+
 class NewRenderTestController < ActionController::Base
   layout :determine_layout
 
@@ -136,7 +139,15 @@ class NewRenderTestController < ActionController::Base
   def partial_with_locals
     render :partial => "customer", :locals => { :customer => Customer.new("david") } 
   end
+
+  def partial_with_form_builder
+    render :partial => ActionView::Helpers::FormBuilder.new(:post, nil, @template, nil, Proc.new {})
+  end
   
+  def partial_with_form_builder_subclass
+    render :partial => LabellingFormBuilder.new(:post, nil, @template, nil, Proc.new {})
+  end
+
   def partial_collection
     render :partial => "customer", :collection => [ Customer.new("david"), Customer.new("mary") ]
   end
@@ -685,6 +696,18 @@ EOS
     assert_equal "Hello: david", @response.body
   end
 
+  def test_partial_with_form_builder
+    get :partial_with_form_builder
+    assert_match(/<label/, @response.body)
+    assert_template('test/_form')
+  end
+
+  def test_partial_with_form_builder_subclass
+    get :partial_with_form_builder_subclass
+    assert_match(/<label/, @response.body)
+    assert_template('test/_labelling_form')
+  end
+
   def test_partial_collection
     get :partial_collection
     assert_equal "Hello: davidHello: mary", @response.body
diff --git a/actionpack/test/fixtures/test/_form.erb b/actionpack/test/fixtures/test/_form.erb
new file mode 100644
index 0000000000..01107f1cb2
--- /dev/null
+++ b/actionpack/test/fixtures/test/_form.erb
@@ -0,0 +1 @@
+<%= form.label :title %>
diff --git a/actionpack/test/fixtures/test/_labelling_form.erb b/actionpack/test/fixtures/test/_labelling_form.erb
new file mode 100644
index 0000000000..1b95763165
--- /dev/null
+++ b/actionpack/test/fixtures/test/_labelling_form.erb
@@ -0,0 +1 @@
+<%= labelling_form.label :title %>