Do not cache ActiveSupport::TimeZone#utc_offset

This can be an issue when TZInfo::TimeZone#current_period is refreshed
due to timezone period transition, but it's not reflected in
ActiveSupport::TimeZone object.

For example, on Sun, 26 Oct 2014 22:00 UTC, Moscow changed its TZ from
MSK +04:00 to MSK +03:00 (-1 hour). If ActiveSupport::TimeZone['Moscow']
happens to be initialized just before the timezone transition, it will
cache its stale utc_offset even after the timezone transition.

This commit removes cache and fixes this issue.

Signed-off-by: Jeremy Daer <jeremydaer@gmail.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/activesupport/test/time_zone_test.rb b/activesupport/test/time_zone_test.rb
index d0674eb03a..a15d5c6a0e 100644
--- a/activesupport/test/time_zone_test.rb
+++ b/activesupport/test/time_zone_test.rb
@@ -395,6 +395,17 @@ class TimeZoneTest < ActiveSupport::TestCase
     assert_equal(-18_000, zone.utc_offset)
   end
 
+  def test_utc_offset_is_not_cached_when_current_period_gets_stale
+    tz = ActiveSupport::TimeZone.create('Moscow')
+    travel_to(Time.utc(2014, 10, 25, 21)) do # 1 hour before TZ change
+      assert_equal 14400, tz.utc_offset, 'utc_offset should be initialized according to current_period'
+    end
+
+    travel_to(Time.utc(2014, 10, 25, 22)) do # after TZ change
+      assert_equal 10800, tz.utc_offset, 'utc_offset should not be cached when current_period gets stale'
+    end
+  end
+
   def test_seconds_to_utc_offset_with_colon
     assert_equal "-06:00", ActiveSupport::TimeZone.seconds_to_utc_offset(-21_600)
     assert_equal "+00:00", ActiveSupport::TimeZone.seconds_to_utc_offset(0)