SerializableResource handles no serializer like controller

CHANGELOG.md

@@ -3,6 +3,7 @@
 Breaking changes:
 
 Features:
+- [#1616](https://github.com/rails-api/active_model_serializers/pull/1616) SerializableResource handles no serializer like controller. (@bf4)
 - [#1618](https://github.com/rails-api/active_model_serializers/issues/1618) Get collection root key for
   empty collection from explicit serializer option, when possible. (@bf4)
 - [#1574](https://github.com/rails-api/active_model_serializers/pull/1574) Provide key translation. (@remear)

lib/action_controller/serialization.rb

@@ -33,20 +33,12 @@ module ActionController
         options[:adapter] = false
       end
       serializable_resource = ActiveModel::SerializableResource.new(resource, options)
-      if serializable_resource.serializer?
       serializable_resource.serialization_scope ||= serialization_scope
       serializable_resource.serialization_scope_name = _serialization_scope
-        begin
-          # Necessary to ensure we have an adapter for the serializable resource
-          # after it has been figured.
-          # TODO: This logic should be less opaque and probably moved into the SerializableResource.
-          serializable_resource.tap(&:adapter)
-        rescue ActiveModel::Serializer::CollectionSerializer::NoSerializerError
-          resource
-        end
-      else
-        resource
-      end
+      # For compatibility with the JSON renderer: `json.to_json(options) if json.is_a?(String)`.
+      # Otherwise, since `serializable_resource` is not a string, the renderer would call
+      # `to_json` on a String and given odd results, such as `"".to_json #=> '""'`
+      serializable_resource.adapter.is_a?(String) ? serializable_resource.adapter : serializable_resource
     end
 
     # Deprecated

lib/active_model/serializable_resource.rb

@@ -30,11 +30,19 @@ module ActiveModel
       serializer_opts[:scope_name] = scope_name
     end
 
+    # NOTE: if no adapter is available, returns the resource itself. (i.e. adapter is a no-op)
     def adapter
-      @adapter ||= ActiveModelSerializers::Adapter.create(serializer_instance, adapter_opts)
+      @adapter ||= find_adapter
     end
     alias adapter_instance adapter
 
+    def find_adapter
+      return resource unless serializer?
+      ActiveModelSerializers::Adapter.create(serializer_instance, adapter_opts)
+    rescue ActiveModel::Serializer::CollectionSerializer::NoSerializerError
+      resource
+    end
+
     def serializer_instance
       @serializer_instance ||= serializer.new(resource, serializer_opts)
     end