In a controller, the current controller name should be the default root for collections

lib/action_controller/serialization.rb

@@ -37,6 +37,10 @@ module ActionController
     end
 
     def _render_option_json(json, options)
+      if json.is_a?(Array)
+        options[:root] ||= controller_name
+      end
+
       if json.respond_to?(:active_model_serializer) && (serializer = json.active_model_serializer)
         json = serializer.new(json, serialization_scope, options)
       end

test/serialization_test.rb

@@ -20,10 +20,14 @@ class RenderJsonTest < ActionController::TestCase
     end
 
     def as_json(*)
-      hash = { :object => @object.as_json, :scope => @scope.as_json }
+      hash = { :object => serializable_hash, :scope => @scope.as_json }
       hash.merge!(:options => true) if @options[:options]
       hash
     end
+
+    def serializable_hash
+      @object.as_json
+    end
   end
 
   class JsonSerializable
@@ -91,6 +95,11 @@ class RenderJsonTest < ActionController::TestCase
       render :json => JsonSerializable.new
     end
 
+    def render_json_with_serializer_and_implicit_root
+      @current_user = Struct.new(:as_json).new(:current_user => true)
+      render :json => [JsonSerializable.new]
+    end
+
     def render_json_with_serializer_and_options
       @current_user = Struct.new(:as_json).new(:current_user => true)
       render :json => JsonSerializable.new, :options => true
@@ -172,6 +181,11 @@ class RenderJsonTest < ActionController::TestCase
     assert_match '"object":{"serializable_object":true}', @response.body
   end
 
+  def test_render_json_with_serializer_and_implicit_root
+    get :render_json_with_serializer_and_implicit_root
+    assert_match '"test":[{"serializable_object":true}]', @response.body
+  end
+
   def test_render_json_with_serializer_and_options
     get :render_json_with_serializer_and_options
     assert_match '"scope":{"current_user":true}', @response.body