Fix inconsistent results when parsing large durations and constructing durations from code

    ActiveSupport::Duration.parse('P3Y') == 3.years # It should be true

Duration parsing made independent from any moment of time:
Fixed length in seconds is assigned to each duration part during parsing.

Changed duration of months and years in seconds to more accurate and logical:

 1. The value of 365.2425 days in Gregorian year is more accurate
    as it accounts for every 400th non-leap year.

 2. Month's length is bound to year's duration, which makes
    sensible comparisons like `12.months == 1.year` to be `true`
    and nonsensical ones like `30.days == 1.month` to be `false`.

Calculations on times and dates with durations shouldn't be affected as
duration's numeric value isn't used in calculations, only parts are used.

Methods on `Numeric` like `2.days` now use these predefined durations
to avoid duplicating of duration constants through the codebase and
eliminate creation of intermediate durations.

2 files changed, 6 insertions, 5 deletions

diff --git a/activesupport/test/core_ext/duration_test.rb b/activesupport/test/core_ext/duration_test.rb
index fc0dd41d0e..8c4c08ffd4 100644
--- a/activesupport/test/core_ext/duration_test.rb
+++ b/activesupport/test/core_ext/duration_test.rb
@@ -340,6 +340,7 @@ class DurationTest < ActiveSupport::TestCase
         travel_to Time.utc(2016, 11, 4) do
           assert_equal 604800, ActiveSupport::Duration.parse("P7D").to_i
           assert_equal 604800, ActiveSupport::Duration.parse("P1W").to_i
+          assert_equal ActiveSupport::Duration.parse(3.years.iso8601).to_i, 3.years.to_i
         end
       end
     end
diff --git a/activesupport/test/core_ext/numeric_ext_test.rb b/activesupport/test/core_ext/numeric_ext_test.rb
index 5361b7b708..5f86bf97c8 100644
--- a/activesupport/test/core_ext/numeric_ext_test.rb
+++ b/activesupport/test/core_ext/numeric_ext_test.rb
@@ -12,7 +12,7 @@ class NumericExtTimeAndDateTimeTest < ActiveSupport::TestCase
       10.minutes => 600,
       1.hour + 15.minutes => 4500,
       2.days + 4.hours + 30.minutes => 189000,
-      5.years + 1.month + 1.fortnight => 161589600
+      5.years + 1.month + 1.fortnight => 161624106
     }
   end
 
@@ -61,10 +61,10 @@ class NumericExtTimeAndDateTimeTest < ActiveSupport::TestCase
   end
 
   def test_duration_after_conversion_is_no_longer_accurate
-    assert_equal 30.days.to_i.seconds.since(@now), 1.month.to_i.seconds.since(@now)
-    assert_equal 365.25.days.to_f.seconds.since(@now), 1.year.to_f.seconds.since(@now)
-    assert_equal 30.days.to_i.seconds.since(@dtnow), 1.month.to_i.seconds.since(@dtnow)
-    assert_equal 365.25.days.to_f.seconds.since(@dtnow), 1.year.to_f.seconds.since(@dtnow)
+    assert_equal (1.year / 12).to_i.seconds.since(@now), 1.month.to_i.seconds.since(@now)
+    assert_equal 365.2425.days.to_f.seconds.since(@now), 1.year.to_f.seconds.since(@now)
+    assert_equal (1.year / 12).to_i.seconds.since(@dtnow), 1.month.to_i.seconds.since(@dtnow)
+    assert_equal 365.2425.days.to_f.seconds.since(@dtnow), 1.year.to_f.seconds.since(@dtnow)
   end
 
   def test_add_one_year_to_leap_day