Ensure the adapters honor a custom root option and include meta when required

test/serializers/meta_test.rb

@@ -48,8 +48,8 @@ module ActiveModel
         assert_equal expected, adapter.as_json
       end
 
-      def test_meta_is_not_used_on_arrays
-        serializer = ArraySerializer.new([@blog], root: "blog", meta: {total: 10}, meta_key: "haha_meta")
+      def test_meta_is_not_present_on_arrays_without_root
+        serializer = ArraySerializer.new([@blog], meta: {total: 10})
         adapter = ActiveModel::Serializer::Adapter::Json.new(serializer)
         expected = [{
           id: 1,
@@ -67,11 +67,38 @@ module ActiveModel
         assert_equal expected, adapter.as_json
       end
 
+      def test_meta_is_present_on_arrays_with_root
+        serializer = ArraySerializer.new([@blog], meta: {total: 10}, meta_key: "haha_meta")
+        adapter = ActiveModel::Serializer::Adapter::Json.new(serializer, root: 'blog')
+        expected = {
+          'blog' => [{
+            id: 1,
+            name: "AMS Hints",
+            writer: {
+              id: 2,
+              name: "Steve"
+            },
+            articles: [{
+              id: 3,
+              title: "AMS",
+              body: nil
+            }]
+          }],
+          'haha_meta' => {
+            total: 10
+          }
+        }
+        assert_equal expected, adapter.as_json
+      end
+
       private
 
       def load_adapter(options)
-        serializer = AlternateBlogSerializer.new(@blog, options)
-        ActiveModel::Serializer::Adapter::Json.new(serializer)
+        adapter_opts, serializer_opts =
+          options.partition { |k, _| ActionController::Serialization::ADAPTER_OPTION_KEYS.include? k }.map { |h| Hash[h] }
+
+        serializer = AlternateBlogSerializer.new(@blog, serializer_opts)
+        ActiveModel::Serializer::Adapter::Json.new(serializer, adapter_opts)
       end
     end
   end