Make `Time.zone.parse` to work with JavaScript date strings

Chrome, Safari and Firefox serialize Date objects to strings such
as 'Mon May 28 2012 00:00:00 GMT-0700 (PDT)'. When these strings
are parsed the zone is interpreted as 'GMT-0700' which doesn't
exist in the TzInfo list of timezones.

By taking advantage of the improved date/time handling in 1.9.3
we can use `Date._parse` and the `:offset` value which is parsed
correctly.

Three tests were amended to make them pass:

1.  test_parse_with_old_date

    This needed changing to a different value because the original
    value was before EST was adopted so was being changed to a
    LMT (Local Mean Time) value after the change. It didn't before
    because `DateTime` just has offsets from UTC not timezones.

2.  test_parse_should_not_black_out_system_timezone_dst_jump

    Changed the implementation of this test as the stubs were
    dependent on internal implementation details of the test.
    Confirmed that the modified test still failed when the
    implementation of `parse` was restored to pre-#5571.

3.  test_parse_should_black_out_app_timezone_dst_jump

    Ditto.

Closes #5770.

1 files changed, 16 insertions, 11 deletions

diff --git a/activesupport/lib/active_support/values/time_zone.rb b/activesupport/lib/active_support/values/time_zone.rb
index 0207f53238..1a37d6f2a4 100644
--- a/activesupport/lib/active_support/values/time_zone.rb
+++ b/activesupport/lib/active_support/values/time_zone.rb
@@ -278,18 +278,23 @@ 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.empty?
-      time = Time.parse(str, now) rescue DateTime.parse(str)
-
-      if date_parts[:offset].nil?
-        if date_parts[:hour] && time.hour != date_parts[:hour]
-          time = DateTime.parse(str)
-        end
-
-        ActiveSupport::TimeWithZone.new(nil, self, time)
+      parts = Date._parse(str, false)
+      return if parts.empty?
+
+      time = Time.new(
+        parts.fetch(:year, now.year),
+        parts.fetch(:mon, now.month),
+        parts.fetch(:mday, now.day),
+        parts.fetch(:hour, now.hour),
+        parts.fetch(:min, now.min),
+        parts.fetch(:sec, now.sec) + parts.fetch(:sec_fraction, 0),
+        parts.fetch(:offset, 0)
+      )
+
+      if parts[:offset]
+        TimeWithZone.new(time.utc, self)
       else
-        time.in_time_zone(self)
+        TimeWithZone.new(nil, self, time)
       end
     end