Fix Ruby's Time marshaling bug in pre-1.9 versions of Ruby: utc insta…

…nces are now correctly unmarshaled with a utc zone instead of the system local zone [#900 state:resolved]

activesupport/CHANGELOG

@@ -1,5 +1,7 @@
 *Edge*
 
+* Fix Ruby's Time marshaling bug in pre-1.9 versions of Ruby: utc instances are now correctly unmarshaled with a utc zone instead of the system local zone [#900 state:resolved] [Luca Guidi, Geoff Buesing]
+
 * Add Array#in_groups which splits or iterates over the array in specified number of groups. #579. [Adrian Mugnolo] Example:
 
   a = (1..10).to_a

activesupport/lib/active_support/core_ext/time.rb

@@ -1,11 +1,32 @@
 require 'date'
 require 'time'
 
-# Ruby 1.8-cvs and 1.9 define private Time#to_date
 class Time
+  # Ruby 1.8-cvs and 1.9 define private Time#to_date
   %w(to_date to_datetime).each do |method|
     public method if private_instance_methods.include?(method)
   end
+
+  # Pre-1.9 versions of Ruby have a bug with marshaling Time instances, where utc instances are
+  # unmarshaled in the local zone, instead of utc. We're layering behavior on the _dump and _load
+  # methods so that utc instances can be flagged on dump, and coerced back to utc on load.
+  if RUBY_VERSION < '1.9'
+    class << self
+      alias_method :_original_load, :_load
+      def _load(marshaled_time)
+        time = _original_load(marshaled_time)
+        utc = time.send(:remove_instance_variable, '@marshal_with_utc_coercion')
+        utc ? time.utc : time
+      end
+    end
+
+    alias_method :_original_dump, :_dump
+    def _dump(*args)
+      obj = self.frozen? ? self.dup : self
+      obj.instance_variable_set('@marshal_with_utc_coercion', utc?)
+      obj._original_dump(*args)
+    end
+  end
 end
 
 require 'active_support/core_ext/time/behavior'

activesupport/test/core_ext/time_ext_test.rb

@@ -625,3 +625,37 @@ def with_env_tz(new_tz = 'US/Eastern')
       old_tz ? ENV['TZ'] = old_tz : ENV.delete('TZ')
     end
 end
+
+class TimeExtMarshalingTest < Test::Unit::TestCase
+  def test_marshaling_with_utc_instance
+    t = Time.utc(2000)
+    marshaled = Marshal.dump t
+    unmarshaled = Marshal.load marshaled
+    assert_equal t, unmarshaled
+    assert_equal t.zone, unmarshaled.zone
+  end
+
+  def test_marshaling_with_local_instance  
+    t = Time.local(2000)
+    marshaled = Marshal.dump t
+    unmarshaled = Marshal.load marshaled
+    assert_equal t, unmarshaled
+    assert_equal t.zone, unmarshaled.zone
+  end
+
+  def test_marshaling_with_frozen_utc_instance  
+    t = Time.utc(2000).freeze
+    marshaled = Marshal.dump t
+    unmarshaled = Marshal.load marshaled
+    assert_equal t, unmarshaled
+    assert_equal t.zone, unmarshaled.zone
+  end
+
+  def test_marshaling_with_frozen_local_instance  
+    t = Time.local(2000).freeze
+    marshaled = Marshal.dump t
+    unmarshaled = Marshal.load marshaled
+    assert_equal t, unmarshaled
+    assert_equal t.zone, unmarshaled.zone
+  end
+end