Lazy load cache and session stores

actionpack/lib/action_controller/session_management.rb

-require 'action_controller/session/cookie_store'
-require 'action_controller/session/drb_store'
-require 'action_controller/session/mem_cache_store'
-if Object.const_defined?(:ActiveRecord)
-  require 'action_controller/session/active_record_store'
-end
-
 module ActionController #:nodoc:
   module SessionManagement #:nodoc:
     def self.included(base)
@@ -22,6 +15,8 @@ module ClassMethods
       # <tt>:p_store</tt>, <tt>:drb_store</tt>, <tt>:mem_cache_store</tt>, or
       # <tt>:memory_store</tt>) or your own custom class.
       def session_store=(store)
+        require "action_controller/session/#{store.to_s}" if [:active_record_store, :drb_store, :mem_cache_store].include?(store)
+
         ActionController::CgiRequest::DEFAULT_SESSION_OPTIONS[:database_manager] =
           store.is_a?(Symbol) ? CGI::Session.const_get(store == :drb_store ? "DRbStore" : store.to_s.camelize) : store
       end

actionpack/test/controller/caching_test.rb

 require 'fileutils'
 require 'abstract_unit'
+require "active_support/cache/memory_store"
 
 CACHE_DIR = 'test_cache'
 # Don't change '/../temp/' cavalierly or you might hose something you don't want hosed

actionpack/test/controller/session/mem_cache_store_test.rb

 require 'abstract_unit'
 require 'action_controller/cgi_process'
 require 'action_controller/cgi_ext'
-
+require 'action_controller/session/mem_cache_store'
 
 class CGI::Session
   def cache

activesupport/lib/active_support/cache.rb

@@ -7,10 +7,13 @@ def self.lookup_store(*store_option)
 
       case store
       when Symbol
+        require "active_support/cache/#{store.to_s}"
+
         store_class_name = (store == :drb_store ? "DRbStore" : store.to_s.camelize)
         store_class = ActiveSupport::Cache.const_get(store_class_name)
         store_class.new(*parameters)
       when nil
+        require "active_support/cache/memory_store"
         ActiveSupport::Cache::MemoryStore.new
       else
         store
@@ -137,9 +140,3 @@ def delete_matched(matcher, options = nil) #:nodoc:
     end
   end
 end
-
-require 'active_support/cache/file_store'
-require 'active_support/cache/memory_store'
-require 'active_support/cache/drb_store'
-require 'active_support/cache/mem_cache_store'
-require 'active_support/cache/compressed_mem_cache_store'

activesupport/lib/active_support/cache/drb_store.rb

 require 'drb'
+require 'active_support/cache/memory_store'
 
 module ActiveSupport
   module Cache