1 files changed, 48 insertions, 0 deletions
diff --git a/actionpack/lib/action_controller/form_builder.rb b/actionpack/lib/action_controller/form_builder.rb
new file mode 100644
index 0000000000..f2656ca894
--- /dev/null
+++ b/actionpack/lib/action_controller/form_builder.rb
@@ -0,0 +1,48 @@
+module ActionController
+  # Override the default form builder for all views rendered by this
+  # controller and any of its descendants. Accepts a subclass of
+  # +ActionView::Helpers::FormBuilder+.
+  #
+  # For example, given a form builder:
+  #
+  #   class AdminFormBuilder < ActionView::Helpers::FormBuilder
+  #     def special_field(name)
+  #     end
+  #   end
+  #
+  # The controller specifies a form builder as its default:
+  #
+  #   class AdminAreaController < ApplicationController
+  #     default_form_builder AdminFormBuilder
+  #   end
+  #
+  # Then in the view any form using +form_for+ will be an instance of the
+  # specified form builder:
+  #
+  #   <%= form_for(@instance) do |builder| %>
+  #     <%= builder.special_field(:name) %>
+  #   <% end %>
+  module FormBuilder
+    extend ActiveSupport::Concern
+
+    included do
+      class_attribute :_default_form_builder, instance_accessor: false
+    end
+
+    module ClassMethods
+      # Set the form builder to be used as the default for all forms
+      # in the views rendered by this controller and its subclasses.
+      #
+      # ==== Parameters
+      # * <tt>builder</tt> - Default form builder, an instance of +ActionView::Helpers::FormBuilder+
+      def default_form_builder(builder)
+        self._default_form_builder = builder
+      end
+    end
+
+    # Default form builder for the controller
+    def default_form_builder
+      self.class._default_form_builder
+    end
+  end
+end