Simplify the implementation of custom serialziers

Right now it is only possible to define serializers globally so we don't
need to use a class attribute in the job class.

activejob/lib/active_job/serializers.rb

@@ -33,16 +33,31 @@ module ActiveJob
     autoload :ObjectSerializer
     autoload :StandardTypeSerializer
 
-    included do
-      class_attribute :_additional_serializers, instance_accessor: false, instance_predicate: false
-      self._additional_serializers = []
-    end
+    mattr_accessor :_additional_serializers
+    self._additional_serializers = []
+
+    class << self
+      # Returns serialized representative of the passed object.
+      # Will look up through all known serializers.
+      # Raises `ActiveJob::SerializationError` if it can't find a proper serializer.
+      def serialize(argument)
+        serializer = serializers.detect { |s| s.serialize?(argument) }
+        raise SerializationError.new("Unsupported argument type: #{argument.class.name}") unless serializer
+        serializer.serialize(argument)
+      end
+
+      # Returns deserialized object.
+      # Will look up through all known serializers.
+      # If no serializers found will raise `ArgumentError`
+      def deserialize(argument)
+        serializer = serializers.detect { |s| s.deserialize?(argument) }
+        raise ArgumentError, "Can only deserialize primitive arguments: #{argument.inspect}" unless serializer
+        serializer.deserialize(argument)
+      end
 
-    # Includes the method to list known serializers and to add new ones
-    module ClassMethods
       # Returns list of known serializers
       def serializers
-        self._additional_serializers + ActiveJob::Serializers::SERIALIZERS
+        self._additional_serializers
       end
 
       # Adds a new serializer to a list of known serializers
@@ -68,33 +83,10 @@ module ActiveJob
         end
     end
 
-    # :nodoc:
-    SERIALIZERS = [
-      ::ActiveJob::Serializers::GlobalIDSerializer,
-      ::ActiveJob::Serializers::StandardTypeSerializer,
-      ::ActiveJob::Serializers::HashWithIndifferentAccessSerializer,
-      ::ActiveJob::Serializers::HashSerializer,
-      ::ActiveJob::Serializers::ArraySerializer
-    ].freeze
-
-    class << self
-      # Returns serialized representative of the passed object.
-      # Will look up through all known serializers.
-      # Raises `ActiveJob::SerializationError` if it can't find a proper serializer.
-      def serialize(argument)
-        serializer = ::ActiveJob::Base.serializers.detect { |s| s.serialize?(argument) }
-        raise SerializationError.new("Unsupported argument type: #{argument.class.name}") unless serializer
-        serializer.serialize(argument)
-      end
-
-      # Returns deserialized object.
-      # Will look up through all known serializers.
-      # If no serializers found will raise `ArgumentError`
-      def deserialize(argument)
-        serializer = ::ActiveJob::Base.serializers.detect { |s| s.deserialize?(argument) }
-        raise ArgumentError, "Can only deserialize primitive arguments: #{argument.inspect}" unless serializer
-        serializer.deserialize(argument)
-      end
-    end
+    add_serializers GlobalIDSerializer,
+      StandardTypeSerializer,
+      HashWithIndifferentAccessSerializer,
+      HashSerializer,
+      ArraySerializer
   end
 end

activejob/lib/active_job/serializers/hash_serializer.rb

@@ -38,7 +38,7 @@ module ActiveJob
         def serialize_hash_key(key)
           raise SerializationError.new("Only string and symbol hash keys may be serialized as job arguments, but #{key.inspect} is a #{key.class}") unless [String, Symbol].include?(key.class)
 
-          raise SerializationError.new("Can't serialize a Hash with reserved key #{key.inspect}") if ActiveJob::Base.reserved_serializers_keys.include?(key.to_s)
+          raise SerializationError.new("Can't serialize a Hash with reserved key #{key.inspect}") if ActiveJob::Serializers.reserved_serializers_keys.include?(key.to_s)
 
           key.to_s
         end

activejob/test/cases/serializers_test.rb

@@ -36,7 +36,11 @@ class SerializersTest < ActiveSupport::TestCase
 
   setup do
     @value_object = DummyValueObject.new 123
-    ActiveJob::Base._additional_serializers = []
+    @original_serializers = ActiveJob::Serializers.serializers
+  end
+
+  teardown do
+    ActiveJob::Serializers._additional_serializers = @original_serializers
   end
 
   test "can't serialize unknown object" do
@@ -51,14 +55,14 @@ class SerializersTest < ActiveSupport::TestCase
   end
 
   test "adds new serializer" do
-    ActiveJob::Base.add_serializers DummySerializer
-    assert ActiveJob::Base.serializers.include?(DummySerializer)
+    ActiveJob::Serializers.add_serializers DummySerializer
+    assert ActiveJob::Serializers.serializers.include?(DummySerializer)
   end
 
   test "can't add serializer with the same key twice" do
-    ActiveJob::Base.add_serializers DummySerializer
+    ActiveJob::Serializers.add_serializers DummySerializer
     assert_raises ArgumentError do
-      ActiveJob::Base.add_serializers DummySerializer
+      ActiveJob::Serializers.add_serializers DummySerializer
     end
   end
 end