[WIP] Move root option handling to adapter

lib/active_model/serializer.rb

@@ -19,7 +19,7 @@
 module ActiveModel
   class Serializer
     # @see #serializable_hash for more details on these valid keys.
-    SERIALIZABLE_HASH_VALID_KEYS = [:only, :except, :methods, :include, :root].freeze
+    SERIALIZABLE_HASH_VALID_KEYS = [:only, :except, :methods, :include].freeze
     extend ActiveSupport::Autoload
     autoload :Adapter
     autoload :Null
@@ -114,15 +114,14 @@ def self.serialization_adapter_instance
       @serialization_adapter_instance ||= ActiveModelSerializers::Adapter::Attributes
     end
 
-    attr_accessor :object, :root, :scope
+    attr_accessor :object, :scope
 
     # `scope_name` is set as :current_user by default in the controller.
     # If the instance does not have a method named `scope_name`, it
     # defines the method so that it calls the +scope+.
     def initialize(object, options = {})
       self.object = object
       self.instance_options = options
-      self.root = instance_options[:root]
       self.scope = instance_options[:scope]
 
       scope_name = instance_options[:scope_name]
@@ -178,8 +177,7 @@ def serializable_hash(adapter_options = nil, options = {}, adapter_instance = se
     # TODO: When moving attributes adapter logic here, @see #serializable_hash
     # So that the below is true:
     #   @param options [nil, Hash] The same valid options passed to `as_json`
-    #      (:root, :only, :except, :methods, and :include).
-    #   The default for `root` is nil.
+    #      (:only, :except, :methods, and :include).
     #   The default value for include_root is false. You can change it to true if the given
     #   JSON string includes a single root node.
     def as_json(adapter_opts = nil)
@@ -188,7 +186,7 @@ def as_json(adapter_opts = nil)
 
     # Used by adapter as resource root.
     def json_key
-      root || _type || object.class.model_name.to_s.underscore
+      _type || object.class.model_name.to_s.underscore
     end
 
     def read_attribute_for_serialization(attr)

lib/active_model/serializer/collection_serializer.rb

@@ -5,12 +5,11 @@ class CollectionSerializer
       include Enumerable
       delegate :each, to: :@serializers
 
-      attr_reader :object, :root
+      attr_reader :object
 
       def initialize(resources, options = {})
         @object                  = resources
         @options                 = options
-        @root                    = options[:root]
         @serializers             = serializers_from_resources
       end
 
@@ -37,7 +36,6 @@ def serializable_hash(adapter_options, options, adapter_instance)
       # Disabling cop since it's good to highlight the complexity of this method by
       # including all the logic right here.
       def json_key
-        return root if root
         # 1. get from options[:serializer] for empty resource collection
         key = object.empty? &&
           (explicit_serializer_class = options[:serializer]) &&

lib/active_model_serializers/adapter/base.rb

@@ -74,10 +74,6 @@ def fragment_cache(cached_hash, non_cached_hash)
       def serialization_options(options)
         options ||= {} # rubocop:disable Lint/UselessAssignment
       end
-
-      def root
-        serializer.json_key.to_sym if serializer.json_key
-      end
     end
   end
 end

lib/active_model_serializers/adapter/json.rb

@@ -9,6 +9,14 @@ def serializable_hash(options = nil)
         self.class.transform_key_casing!(serialized_hash, instance_options)
       end
 
+      def root
+        if instance_options.key?(:root)
+          instance_options[:root]
+        elsif serializer.json_key
+          serializer.json_key.to_sym
+        end
+      end
+
       def meta
         instance_options.fetch(:meta, nil)
       end

lib/active_model_serializers/serializable_resource.rb

@@ -2,7 +2,9 @@
 
 module ActiveModelSerializers
   class SerializableResource
-    ADAPTER_OPTION_KEYS = Set.new([:include, :fields, :adapter, :meta, :meta_key, :links, :serialization_context, :key_transform])
+    ADAPTER_OPTION_KEYS = Set.new([:include, :fields, :adapter, :meta,
+                                   :meta_key, :links, :root,
+                                   :serialization_context, :key_transform])
     include ActiveModelSerializers::Logging
 
     delegate :serializable_hash, :as_json, :to_json, to: :adapter