Fix `ActiveSupport::TimeZone.parse` when time is a local DST jump

The previous implementation `ActiveSupport::TimeZone.parse` used `Time.parse`
which applies the system time DST rules to the parsed time. Instead we now
use `Time.utc` and manually apply the offset.

Backport tests from:
005d910624bbfa724b638426a000c8074d4201a2
c89b6c4cdce7ee55ed3665c099d914222fe0344a
03becb13099c439f6aea5058546bc8b0b19b8db8

Fixes #9678.

3 files changed, 76 insertions, 7 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 528de79cf6..bade1ea4e2 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,6 +1,9 @@
 ## unreleased ##
 
-*   No changes.
+*   Fix `ActiveSupport::TimeZone.parse` when time is at a local DST jump.
+    Fixes #9678.
+
+    *Andrew White*
 
 
 ## Rails 3.2.13.rc1 (Feb 17, 2013) ##
diff --git a/activesupport/lib/active_support/values/time_zone.rb b/activesupport/lib/active_support/values/time_zone.rb
index c7d8fc2e17..f935180036 100644
--- a/activesupport/lib/active_support/values/time_zone.rb
+++ b/activesupport/lib/active_support/values/time_zone.rb
@@ -268,13 +268,23 @@ module ActiveSupport
     #   Time.zone.now                 # => Fri, 31 Dec 1999 14:00:00 HST -10:00
     #   Time.zone.parse('22:30:00')   # => Fri, 31 Dec 1999 22:30:00 HST -10:00
     def parse(str, now=now)
-      date_parts = Date._parse(str)
-      return if date_parts.blank?
-      time = Time.parse(str, now) rescue DateTime.parse(str)
-      if date_parts[:offset].nil?
-        ActiveSupport::TimeWithZone.new(nil, self, time)
+      parts = Date._parse(str, false)
+      return if parts.empty?
+
+      time = Time.utc(
+        parts.fetch(:year, now.year),
+        parts.fetch(:mon, now.month),
+        parts.fetch(:mday, now.day),
+        parts.fetch(:hour, 0),
+        parts.fetch(:min, 0),
+        parts.fetch(:sec, 0),
+        parts.fetch(:sec_fraction, 0) * 1000000
+      )
+
+      if parts[:offset]
+        TimeWithZone.new(time - parts[:offset], self)
       else
-        time.in_time_zone(self)
+        TimeWithZone.new(nil, self, time)
       end
     end
 
diff --git a/activesupport/test/time_zone_test.rb b/activesupport/test/time_zone_test.rb
index 8ecfc1e47e..bd4bfca82c 100644
--- a/activesupport/test/time_zone_test.rb
+++ b/activesupport/test/time_zone_test.rb
@@ -198,6 +198,62 @@ class TimeZoneTest < Test::Unit::TestCase
     assert_equal Time.utc(1999,12,31,19), twz.time
   end
 
+  def test_parse_should_not_black_out_system_timezone_dst_jump
+    with_env_tz('EET') do
+      zone = ActiveSupport::TimeZone['Pacific Time (US & Canada)']
+      twz = zone.parse('2012-03-25 03:29:00')
+      assert_equal [0, 29, 3, 25, 3, 2012], twz.to_a[0,6]
+    end
+  end
+
+  def test_parse_should_black_out_app_timezone_dst_jump
+    with_env_tz('EET') do
+      zone = ActiveSupport::TimeZone['Pacific Time (US & Canada)']
+      twz = zone.parse('2012-03-11 02:29:00')
+      assert_equal [0, 29, 3, 11, 3, 2012], twz.to_a[0,6]
+    end
+  end
+
+  def test_parse_with_javascript_date
+    zone = ActiveSupport::TimeZone['Eastern Time (US & Canada)']
+    twz = zone.parse("Mon May 28 2012 00:00:00 GMT-0700 (PDT)")
+    assert_equal Time.utc(2012, 5, 28, 7, 0, 0), twz.utc
+  end
+
+  def test_parse_with_missing_time_components
+    zone = ActiveSupport::TimeZone['Eastern Time (US & Canada)']
+    zone.stubs(:now).returns zone.local(1999, 12, 31, 12, 59, 59)
+    twz = zone.parse('2012-12-01')
+    assert_equal Time.utc(2012, 12, 1), twz.time
+  end
+
+  def test_parse_doesnt_use_local_dst
+    with_env_tz 'US/Eastern' do
+      zone = ActiveSupport::TimeZone['UTC']
+      twz = zone.parse('2013-03-10 02:00:00')
+      assert_equal Time.utc(2013, 3, 10, 2, 0, 0), twz.time
+    end
+  end
+
+  def test_parse_handles_dst_jump
+    with_env_tz 'US/Eastern' do
+      zone = ActiveSupport::TimeZone['Eastern Time (US & Canada)']
+      twz = zone.parse('2013-03-10 02:00:00')
+      assert_equal Time.utc(2013, 3, 10, 3, 0, 0), twz.time
+    end
+  end
+
+  def test_parse_with_fractional_seconds
+    zone = ActiveSupport::TimeZone['Eastern Time (US & Canada)']
+    twz = zone.parse('2013-03-13 00:00:00.000001')
+    assert_equal 1, twz.usec
+
+    if twz.respond_to?(:nsec)
+      twz = zone.parse('2013-03-13 00:00:00.000000001')
+      assert_equal 1, twz.nsec
+    end
+  end
+
   def test_utc_offset_lazy_loaded_from_tzinfo_when_not_passed_in_to_initialize
     tzinfo = TZInfo::Timezone.get('America/New_York')
     zone = ActiveSupport::TimeZone.create(tzinfo.name, nil, tzinfo)