Collapse JSON API success/failure documents in one adapter

Idea per remear (Ben Mills) in the slack:
https://amserializers.slack.com/archives/general/p1455140474000171

remear:

    just so i understand, the adapter in `render json: resource, status: 422, adapter: 'json_api/error',
    serializer: ActiveModel::Serializer::ErrorSerializer` is a different one than, say what i’ve
    specified in a base serializer with `ActiveModel::Serializer.config.adapter = :json_api`. correct?

    and a followup question of, why not same adapter but different serializer?

me:

   With the way the code is written now, it might be possible to not require a special jsonapi adapter.
   However, the behavior is pretty different from the jsonapi adapter.

   this first draft of the PR had it automatically set the adapter if there were errors.  since that
   requires more discussion, I took a step back and made it explicit for this PR

   If I were to re-use the json api adapter and remove the error one, it think the serializable hash
   method would look like

   ```
   def serializable_hash(options = nil)
     return { errors: JsonApi::Error.collection_errors } if serializer.is_a?(ErrorsSerializer)
     return { errors: JsonApi::Error.resource_errors(serializer) } if serializer.is_a?(ErrorSerializer)
     options ||= {}
   ```

   I suppose it could be something more duckish like

   ```
   def serializable_hash(options = nil)
     if serializer.errors? # object.errors.any? || object.any? {|o| o.errors.any? }
       JsonApi::Error.new(serializer).serializable_hash
     else
       # etc
   ```

docs/jsonapi/errors.md

@@ -2,9 +2,8 @@
 
 # JSON API Errors
 
-Rendering error documents requires specifying the serializer and the adapter:
+Rendering error documents requires specifying the error serializer(s):
 
-- `adapter: :'json_api/error'`
 - Serializer:
   - For a single resource: `serializer: ActiveModel::Serializer::ErrorSerializer`.
   - For a collection: `serializer: ActiveModel::Serializer::ErrorsSerializer`, `each_serializer: ActiveModel::Serializer::ErrorSerializer`.
@@ -23,7 +22,7 @@ resource.errors.add(:name, 'cannot be nil')
 resource.errors.add(:name, 'must be longer')
 resource.errors.add(:id, 'must be a uuid')
 
-render json: resource, status: 422, adapter: 'json_api/error', serializer: ActiveModel::Serializer::ErrorSerializer
+render json: resource, status: 422, adapter: :json_api, serializer: ActiveModel::Serializer::ErrorSerializer
 # #=>
 #  { :errors =>
 #    [
@@ -44,7 +43,7 @@ resource.errors.add(:name, 'must be awesome')
 serializable_resource = ActiveModel::SerializableResource.new(
   resource, {
     serializer: ActiveModel::Serializer::ErrorSerializer,
-    adapter: 'json_api/error'
+    adapter: :json_api
   })
 serializable_resource.as_json(options)
 # #=>

lib/active_model/serializer.rb

@@ -118,6 +118,10 @@ module ActiveModel
       end
     end
 
+    def success?
+      true
+    end
+
     # Used by adapter as resource root.
     def json_key
       root || object.class.model_name.to_s.underscore

lib/active_model/serializer/collection_serializer.rb

@@ -22,6 +22,10 @@ module ActiveModel
         end
       end
 
+      def success?
+        true
+      end
+
       def json_key
         root || derived_root
       end

lib/active_model/serializer/error_serializer.rb

@@ -3,4 +3,8 @@ class ActiveModel::Serializer::ErrorSerializer < ActiveModel::Serializer
   def as_json
     object.errors.messages
   end
+
+  def success?
+    false
+  end
 end

lib/active_model/serializer/errors_serializer.rb

@@ -1,5 +1,5 @@
 require 'active_model/serializer/error_serializer'
-class ActiveModel::Serializer::ErrorsSerializer < ActiveModel::Serializer
+class ActiveModel::Serializer::ErrorsSerializer
   include Enumerable
   delegate :each, to: :@serializers
   attr_reader :object, :root
@@ -13,6 +13,10 @@ class ActiveModel::Serializer::ErrorsSerializer < ActiveModel::Serializer
     end
   end
 
+  def success?
+    false
+  end
+
   def json_key
     nil
   end

lib/active_model_serializers/adapter/json_api.rb

@@ -53,7 +53,14 @@ module ActiveModelSerializers
 
       def serializable_hash(options = nil)
         options ||= {}
+        if serializer.success?
+          success_document(options)
+        else
+          failure_document
+        end
+      end
 
+      def success_document(options)
         is_collection = serializer.respond_to?(:each)
         serializers = is_collection ? serializer : [serializer]
         primary_data, included = resource_objects_for(serializers)
@@ -77,6 +84,28 @@ module ActiveModelSerializers
         hash
       end
 
+      # TODO: look into caching
+      # rubocop:disable Style/AsciiComments
+      # definition:
+      #   ☑ toplevel_errors array (required)
+      #   ☐ toplevel_meta
+      #   ☐ toplevel_jsonapi
+      # rubocop:enable Style/AsciiComments
+      def failure_document
+        hash = {}
+        # PR Please :)
+        # ApiObjects::Jsonapi.add!(hash)
+
+        if serializer.respond_to?(:each)
+          hash[:errors] = serializer.flat_map do |error_serializer|
+            Error.resource_errors(error_serializer)
+          end
+        else
+          hash[:errors] = Error.resource_errors(serializer)
+        end
+        hash
+      end
+
       def fragment_cache(cached_hash, non_cached_hash)
         root = false if instance_options.include?(:include)
         ActiveModelSerializers::Adapter::JsonApi::FragmentCache.new.fragment_cache(root, cached_hash, non_cached_hash)

lib/active_model_serializers/adapter/json_api/error.rb

@@ -1,29 +1,13 @@
 module ActiveModelSerializers
   module Adapter
     class JsonApi < Base
-      class Error < Base
-        UnknownSourceTypeError = Class.new(ArgumentError)
+      module Error
         # rubocop:disable Style/AsciiComments
-        # TODO: look into caching
-
-        # definition:
-        #   ☐ toplevel_errors array (required)
-        #   ☑ toplevel_meta
-        #   ☑ toplevel_jsonapi
-        def serializable_hash(*)
-          hash = {}
-          # PR Please :)
-          # Jsonapi.add!(hash)
-
-          # Checking object since we're not using an ArraySerializer
-          if serializer.object.respond_to?(:each)
-            hash[:errors] = collection_errors
-          else
-            hash[:errors] = Error.resource_errors(serializer)
-          end
-          hash
-        end
+        UnknownSourceTypeError = Class.new(ArgumentError)
 
+        # Builds a JSON API Errors Object
+        # {http://jsonapi.org/format/#errors JSON API Errors}
+        #
         # @param [ActiveModel::Serializer::ErrorSerializer]
         # @return [Array<Symbol, Array<String>] i.e. attribute_name, [attribute_errors]
         def self.resource_errors(error_serializer)
@@ -86,16 +70,6 @@ module ActiveModelSerializers
             fail UnknownSourceTypeError, "Unknown source type '#{source_type}' for attribute_name '#{attribute_name}'"
           end
         end
-
-        private
-
-        # @return [Array<#object_errors>]
-        def collection_errors
-          serializer.flat_map do |error_serializer|
-            Error.resource_errors(error_serializer)
-          end
-        end
-
         # rubocop:enable Style/AsciiComments
       end
     end

test/action_controller/json_api/errors_test.rb

@@ -30,7 +30,7 @@ module ActionController
             resource.errors.add(:name, 'cannot be nil')
             resource.errors.add(:name, 'must be longer')
             resource.errors.add(:id, 'must be a uuid')
-            render json: resource, adapter: 'json_api/error', serializer: ActiveModel::Serializer::ErrorSerializer
+            render json: resource, adapter: :json_api, serializer: ActiveModel::Serializer::ErrorSerializer
           end
         end
 

test/active_model_serializers/adapter_for_test.rb

@@ -102,8 +102,7 @@ module ActiveModelSerializers
         'null'.freeze              => ActiveModelSerializers::Adapter::Null,
         'json'.freeze              => ActiveModelSerializers::Adapter::Json,
         'attributes'.freeze => ActiveModelSerializers::Adapter::Attributes,
-        'json_api'.freeze => ActiveModelSerializers::Adapter::JsonApi,
-        'json_api/error'.freeze => ActiveModelSerializers::Adapter::JsonApi::Error
+        'json_api'.freeze => ActiveModelSerializers::Adapter::JsonApi
       }
       actual = ActiveModelSerializers::Adapter.adapter_map
       assert_equal actual, expected_adapter_map
@@ -114,7 +113,6 @@ module ActiveModelSerializers
         'attributes'.freeze,
         'json'.freeze,
         'json_api'.freeze,
-        'json_api/error'.freeze,
         'null'.freeze
       ]
     end

test/adapter/json_api/errors_test.rb

@@ -13,7 +13,7 @@ module ActiveModelSerializers
         def test_active_model_with_error
           options = {
               serializer: ActiveModel::Serializer::ErrorSerializer,
-              adapter: :'json_api/error'
+              adapter: :json_api
           }
 
           @resource.errors.add(:name, 'cannot be nil')
@@ -37,7 +37,7 @@ module ActiveModelSerializers
         def test_active_model_with_multiple_errors
           options = {
               serializer: ActiveModel::Serializer::ErrorSerializer,
-              adapter: :'json_api/error'
+              adapter: :json_api
           }
 
           @resource.errors.add(:name, 'cannot be nil')

test/serializable_resource_test.rb

@@ -40,7 +40,7 @@ module ActiveModel
         serializable_resource = ActiveModel::SerializableResource.new(
           resource, {
             serializer: ActiveModel::Serializer::ErrorSerializer,
-            adapter: 'json_api/error'
+            adapter: :json_api
           })
         expected_response_document =
           { :errors =>
@@ -61,7 +61,7 @@ module ActiveModel
           resources, {
             serializer: ActiveModel::Serializer::ErrorsSerializer,
             each_serializer: ActiveModel::Serializer::ErrorSerializer,
-            adapter: 'json_api/error'
+            adapter: :json_api
           })
         expected_response_document =
           { :errors =>