Move default_form_builder to ActionView so it'll work in environments not using ActionView::Base

actionpack/lib/action_view/helpers/form_helper.rb

@@ -488,7 +488,7 @@ def fields_for(record_or_name_or_array, *args, &block)
           object_name = ActionController::RecordIdentifier.singular_class_name(object)
         end
 
-        builder = options[:builder] || ActionView::Base.default_form_builder
+        builder = options[:builder] || ActionView.default_form_builder
         yield builder.new(object_name, object, self, options, block)
       end
 
@@ -1054,9 +1054,21 @@ def nested_child_index(name)
     end
   end
 
-  class << Base
+  class << ActionView
     attr_accessor :default_form_builder
   end
 
-  Base.default_form_builder = ::ActionView::Helpers::FormBuilder
+  self.default_form_builder = ::ActionView::Helpers::FormBuilder
+
+  # 2.3 compatibility
+  class << Base
+    def default_form_builder=(builder)
+      ActionView.default_form_builder = builder
+    end
+
+    def default_form_builder
+      ActionView.default_form_builder
+    end
+  end
+
 end

actionpack/test/template/form_helper_test.rb

@@ -1024,8 +1024,8 @@ def test_form_for_with_labelled_builder
   end
 
   def test_default_form_builder
-    old_default_form_builder, ActionView::Base.default_form_builder =
-      ActionView::Base.default_form_builder, LabelledFormBuilder
+    old_default_form_builder, ActionView.default_form_builder =
+      ActionView.default_form_builder, LabelledFormBuilder
 
     form_for(:post, @post) do |f|
       concat f.text_field(:title)
@@ -1042,7 +1042,7 @@ def test_default_form_builder
 
     assert_dom_equal expected, output_buffer
   ensure
-    ActionView::Base.default_form_builder = old_default_form_builder
+    ActionView.default_form_builder = old_default_form_builder
   end
 
   def test_default_form_builder_with_active_record_helpers