Serialize classes and modules with ActiveJob

This commit allows ActiveJob to serialize classes and modules without a custom serializer. This allows for workflows like:

```
class EmailJob < ApplicationJob
  queue_as :default
  def perform(template_class, *arguments)
    template_class.new(*arguments).send!
  end
end

module Email
  class FooTemplate ... end
  class BarTemplate ... end
end

EmailJob.perform_later(Email::FooTemplate, ...)
EmailJob.perform_later(Email::BarTemplate, ...)
```

Currently this is only achieveable through a custom serializer or through constantizing in each instance.

activejob/CHANGELOG.md

@@ -1,3 +1,7 @@
+*   Allow `Class` and `Module` instances to be serialized.
+
+    *Kevin Deisz*
+
 *   Log potential matches in `assert_enqueued_with` and `assert_performed_with`
 
     *Gareth du Plooy*

activejob/lib/active_job/serializers.rb

@@ -15,6 +15,7 @@ module ActiveJob
     autoload :DateSerializer
     autoload :TimeWithZoneSerializer
     autoload :TimeSerializer
+    autoload :ModuleSerializer
 
     mattr_accessor :_additional_serializers
     self._additional_serializers = Set.new
@@ -58,6 +59,7 @@ module ActiveJob
       DateTimeSerializer,
       DateSerializer,
       TimeWithZoneSerializer,
-      TimeSerializer
+      TimeSerializer,
+      ModuleSerializer
   end
 end

activejob/lib/active_job/serializers/module_serializer.rb

@@ -0,0 +1,20 @@
+# frozen_string_literal: true
+
+module ActiveJob
+  module Serializers
+    class ModuleSerializer < ObjectSerializer # :nodoc:
+      def serialize(constant)
+        super("value" => constant.name)
+      end
+
+      def deserialize(hash)
+        hash["value"].constantize
+      end
+
+      private
+        def klass
+          Module
+        end
+    end
+  end
+end

activejob/test/cases/argument_serialization_test.rb

@@ -8,6 +8,12 @@ require "jobs/kwargs_job"
 require "support/stubs/strong_parameters"
 
 class ArgumentSerializationTest < ActiveSupport::TestCase
+  module ModuleArgument
+    class ClassArgument; end
+  end
+
+  class ClassArgument; end
+
   setup do
     @person = Person.find("5")
   end
@@ -18,14 +24,17 @@ class ArgumentSerializationTest < ActiveSupport::TestCase
     DateTime.new(2001, 2, 3, 4, 5, 6, "+03:00"),
     ActiveSupport::TimeWithZone.new(Time.utc(1999, 12, 31, 23, 59, 59), ActiveSupport::TimeZone["UTC"]),
     [ 1, "a" ],
-    { "a" => 1 }
+    { "a" => 1 },
+    ModuleArgument,
+    ModuleArgument::ClassArgument,
+    ClassArgument
   ].each do |arg|
     test "serializes #{arg.class} - #{arg} verbatim" do
       assert_arguments_unchanged arg
     end
   end
 
-  [ Object.new, self, Person.find("5").to_gid ].each do |arg|
+  [ Object.new, Person.find("5").to_gid ].each do |arg|
     test "does not serialize #{arg.class}" do
       assert_raises ActiveJob::SerializationError do
         ActiveJob::Arguments.serialize [ arg ]

guides/source/active_job_basics.md

@@ -355,6 +355,8 @@ ActiveJob supports the following types of arguments by default:
   - `Hash` (Keys should be of `String` or `Symbol` type)
   - `ActiveSupport::HashWithIndifferentAccess`
   - `Array`
+  - `Module`
+  - `Class`
 
 ### GlobalID