Change callbacks to automatically include DescendantsTracker and rename descendents to descendants.

activesupport/lib/active_support/callbacks.rb

+require 'active_support/descendants_tracker'
 require 'active_support/core_ext/array/wrap'
 require 'active_support/core_ext/class/inheritable_attributes'
-require 'active_support/core_ext/class/subclasses'
 require 'active_support/core_ext/kernel/reporting'
 require 'active_support/core_ext/kernel/singleton_class'
 
@@ -85,6 +85,10 @@ module ActiveSupport
   module Callbacks
     extend Concern
 
+    included do
+      extend ActiveSupport::DescendantsTracker
+    end
+
     def run_callbacks(kind, *args, &block)
       send("_run_#{kind}_callbacks", *args, &block)
     end
@@ -428,7 +432,7 @@ def __update_callbacks(name, filters = [], block = nil) #:nodoc:
         options = filters.last.is_a?(Hash) ? filters.pop : {}
         filters.unshift(block) if block
 
-        ([self] + self.descendents).each do |target|
+        ([self] + self.descendants).each do |target|
           chain = target.send("_#{name}_callbacks")
           yield chain, type, filters, options
           target.__define_runner(name)
@@ -502,7 +506,7 @@ def skip_callback(name, *filter_list, &block)
       def reset_callbacks(symbol)
         callbacks = send("_#{symbol}_callbacks")
 
-        self.descendents.each do |target|
+        self.descendants.each do |target|
           chain = target.send("_#{symbol}_callbacks")
           callbacks.each { |c| chain.delete(c) }
           target.__define_runner(symbol)

activesupport/lib/active_support/core_ext/class/subclasses.rb

@@ -11,9 +11,9 @@ def subclasses
 
   # Rubinius
   if defined?(Class.__subclasses__)
-    def descendents
+    def descendants
       subclasses = []
-      __subclasses__.each {|k| subclasses << k; subclasses.concat k.descendents }
+      __subclasses__.each {|k| subclasses << k; subclasses.concat k.descendants }
       subclasses
     end
   else
@@ -21,7 +21,7 @@ def descendents
     begin
       ObjectSpace.each_object(Class.new) {}
 
-      def descendents
+      def descendants
         subclasses = []
         ObjectSpace.each_object(class << self; self; end) do |k|
           subclasses << k unless k == self
@@ -30,7 +30,7 @@ def descendents
       end
     # JRuby
     rescue StandardError
-      def descendents
+      def descendants
         subclasses = []
         ObjectSpace.each_object(Class) do |k|
           subclasses << k if k < self
@@ -48,7 +48,7 @@ def descendents
   def self.subclasses_of(*superclasses) #:nodoc:
     subclasses = []
     superclasses.each do |klass|
-      subclasses.concat klass.descendents.select {|k| k.anonymous? || k.reachable?}
+      subclasses.concat klass.descendants.select {|k| k.anonymous? || k.reachable?}
     end
     subclasses
   end

activesupport/test/descendants_tracker_test.rb

 require 'abstract_unit'
 require 'test/unit'
 require 'active_support'
+require 'active_support/core_ext/hash/slice'
 
 class DescendantsTrackerTest < Test::Unit::TestCase
   class Parent
@@ -19,6 +20,8 @@ class Grandchild1 < Child1
   class Grandchild2 < Child1
   end
 
+  ALL = [Parent, Child1, Child2, Grandchild1, Grandchild2]
+
   def test_descendants
     assert_equal [Child1, Grandchild1, Grandchild2, Child2], Parent.descendants
     assert_equal [Grandchild1, Grandchild2], Child1.descendants
@@ -32,9 +35,9 @@ def test_direct_descendants
   end
 
   def test_clear_with_autoloaded_parent_children_and_granchildren
-    mark_as_autoloaded Parent, Child1, Child2, Grandchild1, Grandchild2 do
+    mark_as_autoloaded *ALL do
       ActiveSupport::DescendantsTracker.clear
-      assert_equal Hash.new, ActiveSupport::DescendantsTracker.descendants
+      assert ActiveSupport::DescendantsTracker.descendants.slice(*ALL).empty?
     end
   end