RFC: Json Api Errors (WIP)

- ActiveModelSerializers::JsonPointer
- ActiveModel::Serializer::Adapter::JsonApi::Error
- ActiveModel::Serializer::Adapter::JsonApi::Error.attributes
- Fix rubocop config

lib/active_model/serializable_resource.rb

@@ -16,6 +16,19 @@ module ActiveModel
       @resource = resource
       @adapter_opts, @serializer_opts =
         options.partition { |k, _| ADAPTER_OPTION_KEYS.include? k }.map { |h| Hash[h] }
+
+      # TECHDEBT: clean up single vs. collection of resources
+      if resource.respond_to?(:each)
+        if resource.any? { |elem| elem.respond_to?(:errors) && !elem.errors.empty? }
+          @serializer_opts[:serializer] = ActiveModel::Serializer::ErrorSerializer
+          @adapter_opts[:adapter] = :'json_api/error'
+        end
+      else
+        if resource.respond_to?(:errors) && !resource.errors.empty?
+          @serializer_opts[:serializer] = ActiveModel::Serializer::ErrorSerializer
+          @adapter_opts[:adapter] = :'json_api/error'
+        end
+      end
     end
 
     def serialization_scope=(scope)

lib/active_model/serializer.rb

@@ -1,6 +1,7 @@
 require 'thread_safe'
 require 'active_model/serializer/collection_serializer'
 require 'active_model/serializer/array_serializer'
+require 'active_model/serializer/error_serializer'
 require 'active_model/serializer/include_tree'
 require 'active_model/serializer/associations'
 require 'active_model/serializer/attributes'

lib/active_model/serializer/error_serializer.rb

@@ -0,0 +1,2 @@
+class ActiveModel::Serializer::ErrorSerializer < ActiveModel::Serializer
+end

lib/active_model/serializer/lint.rb

@@ -129,6 +129,20 @@ module ActiveModel::Serializer::Lint
       assert_instance_of resource_class.model_name, ActiveModel::Name
     end
 
+    def test_active_model_errors
+      assert_respond_to resource, :errors
+    end
+
+    def test_active_model_errors_human_attribute_name
+      assert_respond_to resource.class, :human_attribute_name
+      assert_equal(-2, resource.class.method(:human_attribute_name).arity)
+    end
+
+    def test_active_model_errors_lookup_ancestors
+      assert_respond_to resource.class, :lookup_ancestors
+      assert_equal 0, resource.class.method(:lookup_ancestors).arity
+    end
+
     private
 
     def resource