Don't pluralize the CollectionSerializer#root for #json_key

CHANGELOG.md

@@ -13,6 +13,9 @@ Breaking changes:
         Adapter functions.
     * named `Base` because it's a Rails-ism.
     * It helps to isolate and highlight what the Adapter interface actually is.
+- [#1418](https://github.com/rails-api/active_model_serializers/pull/1418)
+  serialized collections now use the root option as is; now, only the
+  root derived from the serializer or object is always pluralized.
 
 Features:
 

lib/active_model/serializer/collection_serializer.rb

@@ -23,8 +23,7 @@ def initialize(resources, options = {})
       end
 
       def json_key
-        key = root || serializers.first.try(:json_key) || object.try(:name).try(:underscore)
-        key.try(:pluralize)
+        root || derived_root
       end
 
       def paginated?
@@ -36,6 +35,13 @@ def paginated?
       protected
 
       attr_reader :serializers
+
+      private
+
+      def derived_root
+        key = serializers.first.try(:json_key) || object.try(:name).try(:underscore)
+        key.try(:pluralize)
+      end
     end
   end
 end

test/action_controller/serialization_test.rb

@@ -171,7 +171,7 @@ def test_render_array_using_custom_root
         with_adapter :json do
           get :render_array_using_custom_root
         end
-        expected = { custom_roots: [{ name: 'Name 1', description: 'Description 1' }] }
+        expected = { custom_root: [{ name: 'Name 1', description: 'Description 1' }] }
         assert_equal 'application/json', @response.content_type
         assert_equal expected.to_json, @response.body
       end
@@ -181,7 +181,7 @@ def test_render_array_that_is_empty_using_custom_root
           get :render_array_that_is_empty_using_custom_root
         end
 
-        expected = { custom_roots: [] }
+        expected = { custom_root: [] }
         assert_equal 'application/json', @response.content_type
         assert_equal expected.to_json, @response.body
       end

test/collection_serializer_test.rb

@@ -62,8 +62,9 @@ def test_root_with_no_serializers
         assert_equal expected, @serializer.root
       end
 
-      def test_json_key
-        assert_equal 'comments', @serializer.json_key
+      def test_json_key_with_resource_with_serializer
+        singular_key = @serializer.send(:serializers).first.json_key
+        assert_equal singular_key.pluralize, @serializer.json_key
       end
 
       def test_json_key_with_resource_with_name_and_no_serializers
@@ -84,13 +85,15 @@ def test_json_key_with_resource_without_name_and_no_serializers
       end
 
       def test_json_key_with_root
-        serializer = collection_serializer.new(@resource, root: 'custom_root')
-        assert_equal 'custom_roots', serializer.json_key
+        expected = 'custom_root'
+        serializer = collection_serializer.new(@resource, root: expected)
+        assert_equal expected, serializer.json_key
       end
 
       def test_json_key_with_root_and_no_serializers
-        serializer = collection_serializer.new(build_named_collection, root: 'custom_root')
-        assert_equal 'custom_roots', serializer.json_key
+        expected = 'custom_root'
+        serializer = collection_serializer.new(build_named_collection, root: expected)
+        assert_equal expected, serializer.json_key
       end
     end
   end