Keep sub-second resolution when wrapping a DateTime value

Add `DateTime#usec` and `DateTime#nsec` so that `ActiveSupport::TimeWithZone`
keeps sub-second resolution when wrapping a `DateTime` value.

Fixes #10855

2 files changed, 15 insertions, 0 deletions

diff --git a/activesupport/test/core_ext/date_time_ext_test.rb b/activesupport/test/core_ext/date_time_ext_test.rb
index 3e76b8a9b1..571344b728 100644
--- a/activesupport/test/core_ext/date_time_ext_test.rb
+++ b/activesupport/test/core_ext/date_time_ext_test.rb
@@ -327,6 +327,16 @@ class DateTimeExtCalculationsTest < ActiveSupport::TestCase
     assert_equal 946684800, DateTime.civil(1999,12,31,19,0,0,Rational(-5,24)).to_i
   end
 
+  def test_usec
+    assert_equal 0, DateTime.civil(2000).usec
+    assert_equal 500000, DateTime.civil(2000, 1, 1, 0, 0, Rational(1,2)).usec
+  end
+
+  def test_nsec
+    assert_equal 0, DateTime.civil(2000).nsec
+    assert_equal 500000000, DateTime.civil(2000, 1, 1, 0, 0, Rational(1,2)).nsec
+  end
+
   protected
     def with_env_tz(new_tz = 'US/Eastern')
       old_tz, ENV['TZ'] = ENV['TZ'], new_tz
diff --git a/activesupport/test/core_ext/time_with_zone_test.rb b/activesupport/test/core_ext/time_with_zone_test.rb
index 3ce3297874..e8eea27d72 100644
--- a/activesupport/test/core_ext/time_with_zone_test.rb
+++ b/activesupport/test/core_ext/time_with_zone_test.rb
@@ -445,6 +445,11 @@ class TimeWithZoneTest < ActiveSupport::TestCase
     assert_equal 0, twz.usec
   end
 
+  def test_usec_returns_sec_fraction_when_datetime_is_wrapped
+    twz = ActiveSupport::TimeWithZone.new(DateTime.civil(2000, 1, 1, 0, 0, Rational(1,2)), @time_zone)
+    assert_equal 500000, twz.usec
+  end
+
   def test_utc_to_local_conversion_saves_period_in_instance_variable
     assert_nil @twz.instance_variable_get('@period')
     @twz.time