Lazy-require state machine internals when the module is included

activemodel/lib/active_model/state_machine.rb

@@ -1,14 +1,10 @@
-Dir[File.dirname(__FILE__) + "/state_machine/*.rb"].sort.each do |path|
-  filename = File.basename(path)
-  require "active_model/state_machine/#{filename}"
-end
-
 module ActiveModel
   module StateMachine
     class InvalidTransition < Exception
     end
 
     def self.included(base)
+      require 'active_model/state_machine/machine'
       base.extend ClassMethods
     end
 

activemodel/lib/active_model/state_machine/event.rb

@@ -1,3 +1,5 @@
+require 'active_model/state_machine/state_transition'
+
 module ActiveModel
   module StateMachine
     class Event

activemodel/lib/active_model/state_machine/machine.rb

@@ -1,3 +1,6 @@
+require 'active_model/state_machine/state'
+require 'active_model/state_machine/event'
+
 module ActiveModel
   module StateMachine
     class Machine