Maintain proleptic gregorian in Time#advance

Time#advance uses Time#to_date and Date#advance to calculate a new date.
The Date object returned by Time#to_date is constructed with the assumption
that the Time object represents a proleptic gregorian date, but it is
configured to observe the default julian calendar reform date (2299161j)
for purposes of calculating month, date and year:

  Time.new(1582, 10, 4).to_date.to_s           # => "1582-09-24"
  Time.new(1582, 10, 4).to_date.gregorian.to_s # => "1582-10-04"

This patch ensures that when the intermediate Date object is advanced
to yield a new Date object, that the Time object for return is contructed
with a proleptic gregorian month, date and year.

1 files changed, 7 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/time_ext_test.rb b/activesupport/test/core_ext/time_ext_test.rb
index 4e53aff00b..7ff4ea9d65 100644
--- a/activesupport/test/core_ext/time_ext_test.rb
+++ b/activesupport/test/core_ext/time_ext_test.rb
@@ -464,6 +464,13 @@ class TimeExtCalculationsTest < ActiveSupport::TestCase
     assert_equal t, t.advance(:months => 0)
   end
 
+  def test_advance_gregorian_proleptic
+    assert_equal Time.local(1582,10,14,15,15,10), Time.local(1582,10,15,15,15,10).advance(:days => -1)
+    assert_equal Time.local(1582,10,15,15,15,10), Time.local(1582,10,14,15,15,10).advance(:days => 1)
+    assert_equal Time.local(1582,10,5,15,15,10), Time.local(1582,10,4,15,15,10).advance(:days => 1)
+    assert_equal Time.local(1582,10,4,15,15,10), Time.local(1582,10,5,15,15,10).advance(:days => -1)
+  end
+
   def test_last_week
     with_env_tz 'US/Eastern' do
       assert_equal Time.local(2005,2,21), Time.local(2005,3,1,15,15,10).last_week