Partial backport of AS::Duration changes from #27610

Backports the fix to not use an epoch date when calculating durations
along with additional refactoring and tests from these commits:

  cb9d0e4864
  9ae511f550
  2a5ae2b714

DOES NOT backport any changes to the length of durations.

activesupport/CHANGELOG.md

@@ -1,3 +1,16 @@
+*   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.
+
+    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.
+
+    *Andrey Novikov, Andrew White*
+
 *   In Core Extensions, make `MarshalWithAutoloading#load` pass through the second, optional
     argument for `Marshal#load( source [, proc] )`. This way we don't have to do 
     `Marshal.method(:load).super_method.call(sourse, proc)` just to be able to pass a proc.

activesupport/lib/active_support/core_ext/integer/time.rb

@@ -18,12 +18,12 @@ class Integer
   #   # equivalent to Time.now.advance(months: 4, years: 5)
   #   (4.months + 5.years).from_now
   def months
-    ActiveSupport::Duration.new(self * 30.days, [[:months, self]])
+    ActiveSupport::Duration.months(self)
   end
   alias :month :months
 
   def years
-    ActiveSupport::Duration.new(self * 365.25.days.to_i, [[:years, self]])
+    ActiveSupport::Duration.years(self)
   end
   alias :year :years
 end

activesupport/lib/active_support/core_ext/numeric/time.rb

@@ -19,7 +19,7 @@ class Numeric
   #   # equivalent to Time.current.advance(months: 4, years: 5)
   #   (4.months + 5.years).from_now
   def seconds
-    ActiveSupport::Duration.new(self, [[:seconds, self]])
+    ActiveSupport::Duration.seconds(self)
   end
   alias :second :seconds
 
@@ -27,7 +27,7 @@ class Numeric
   #
   #   2.minutes # => 2 minutes
   def minutes
-    ActiveSupport::Duration.new(self * 60, [[:minutes, self]])
+    ActiveSupport::Duration.minutes(self)
   end
   alias :minute :minutes
 
@@ -35,7 +35,7 @@ class Numeric
   #
   #   2.hours # => 2 hours
   def hours
-    ActiveSupport::Duration.new(self * 3600, [[:hours, self]])
+    ActiveSupport::Duration.hours(self)
   end
   alias :hour :hours
 
@@ -43,7 +43,7 @@ class Numeric
   #
   #   2.days # => 2 days
   def days
-    ActiveSupport::Duration.new(self * 24.hours, [[:days, self]])
+    ActiveSupport::Duration.days(self)
   end
   alias :day :days
 
@@ -51,7 +51,7 @@ class Numeric
   #
   #   2.weeks # => 2 weeks
   def weeks
-    ActiveSupport::Duration.new(self * 7.days, [[:weeks, self]])
+    ActiveSupport::Duration.weeks(self)
   end
   alias :week :weeks
 
@@ -59,7 +59,7 @@ class Numeric
   #
   #   2.fortnights # => 4 weeks
   def fortnights
-    ActiveSupport::Duration.new(self * 2.weeks, [[:weeks, self * 2]])
+    ActiveSupport::Duration.weeks(self * 2)
   end
   alias :fortnight :fortnights
 

activesupport/lib/active_support/duration.rb

@@ -7,13 +7,82 @@ module ActiveSupport
   #
   #   1.month.ago       # equivalent to Time.now.advance(months: -1)
   class Duration
-    EPOCH = ::Time.utc(2000)
+    SECONDS_PER_MINUTE = 60
+    SECONDS_PER_HOUR   = 3600
+    SECONDS_PER_DAY    = 86400
+    SECONDS_PER_WEEK   = 604800
+    SECONDS_PER_MONTH  = 2592000  # 30 days
+    SECONDS_PER_YEAR   = 31557600 # length of a julian year (365.2425 days)
+
+    PARTS_IN_SECONDS = {
+      seconds: 1,
+      minutes: SECONDS_PER_MINUTE,
+      hours:   SECONDS_PER_HOUR,
+      days:    SECONDS_PER_DAY,
+      weeks:   SECONDS_PER_WEEK,
+      months:  SECONDS_PER_MONTH,
+      years:   SECONDS_PER_YEAR
+    }.freeze
 
     attr_accessor :value, :parts
 
     autoload :ISO8601Parser,     'active_support/duration/iso8601_parser'
     autoload :ISO8601Serializer, 'active_support/duration/iso8601_serializer'
 
+    class << self
+      # Creates a new Duration from string formatted according to ISO 8601 Duration.
+      #
+      # See {ISO 8601}[http://en.wikipedia.org/wiki/ISO_8601#Durations] for more information.
+      # This method allows negative parts to be present in pattern.
+      # If invalid string is provided, it will raise +ActiveSupport::Duration::ISO8601Parser::ParsingError+.
+      def parse(iso8601duration)
+        parts = ISO8601Parser.new(iso8601duration).parse!
+        new(calculate_total_seconds(parts), parts)
+      end
+
+      def ===(other) #:nodoc:
+        other.is_a?(Duration)
+      rescue ::NoMethodError
+        false
+      end
+
+      def seconds(value) #:nodoc:
+        new(value, [[:seconds, value]])
+      end
+
+      def minutes(value) #:nodoc:
+        new(value * SECONDS_PER_MINUTE, [[:minutes, value]])
+      end
+
+      def hours(value) #:nodoc:
+        new(value * SECONDS_PER_HOUR, [[:hours, value]])
+      end
+
+      def days(value) #:nodoc:
+        new(value * SECONDS_PER_DAY, [[:days, value]])
+      end
+
+      def weeks(value) #:nodoc:
+        new(value * SECONDS_PER_WEEK, [[:weeks, value]])
+      end
+
+      def months(value) #:nodoc:
+        new(value * SECONDS_PER_MONTH, [[:months, value]])
+      end
+
+      def years(value) #:nodoc:
+        new(value * SECONDS_PER_YEAR, [[:years, value]])
+      end
+
+      private
+
+        def calculate_total_seconds(parts)
+          parts.inject(0) do |total, (part, value)|
+            total + value * PARTS_IN_SECONDS[part]
+          end
+        end
+    end
+
     def initialize(value, parts) #:nodoc:
       @value, @parts = value, parts
     end
@@ -99,12 +168,6 @@ module ActiveSupport
       @value.hash
     end
 
-    def self.===(other) #:nodoc:
-      other.is_a?(Duration)
-    rescue ::NoMethodError
-      false
-    end
-
     # Calculates a new Time or Date that is as far in the future
     # as this Duration represents.
     def since(time = ::Time.current)
@@ -135,16 +198,6 @@ module ActiveSupport
       @value.respond_to?(method, include_private)
     end
 
-    # Creates a new Duration from string formatted according to ISO 8601 Duration.
-    #
-    # See {ISO 8601}[http://en.wikipedia.org/wiki/ISO_8601#Durations] for more information.
-    # This method allows negative parts to be present in pattern.
-    # If invalid string is provided, it will raise +ActiveSupport::Duration::ISO8601Parser::ParsingError+.
-    def self.parse(iso8601duration)
-      parts = ISO8601Parser.new(iso8601duration).parse!
-      new(EPOCH.advance(parts) - EPOCH, parts)
-    end
-
     # Build ISO 8601 Duration string for this duration.
     # The +precision+ parameter can be used to limit seconds' precision of duration.
     def iso8601(precision: nil)

activesupport/test/core_ext/duration_test.rb

@@ -233,6 +233,21 @@ class DurationTest < ActiveSupport::TestCase
     assert_equal(1, (61 <=> 1.minute))
   end
 
+  def test_adding_one_month_maintains_day_of_month
+    (1..11).each do |month|
+      [1, 14, 28].each do |day|
+        assert_equal Date.civil(2016, month + 1, day), Date.civil(2016, month, day) + 1.month
+      end
+    end
+
+    assert_equal Date.civil(2017, 1, 1),  Date.civil(2016, 12, 1) + 1.month
+    assert_equal Date.civil(2017, 1, 14),  Date.civil(2016, 12, 14) + 1.month
+    assert_equal Date.civil(2017, 1, 28),  Date.civil(2016, 12, 28) + 1.month
+
+    assert_equal Date.civil(2015, 2, 28), Date.civil(2015, 1, 31) + 1.month
+    assert_equal Date.civil(2016, 2, 29), Date.civil(2016, 1, 31) + 1.month
+  end
+
   # ISO8601 string examples are taken from ISO8601 gem at https://github.com/arnau/ISO8601/blob/b93d466840/spec/iso8601/duration_spec.rb
   # published under the conditions of MIT license at https://github.com/arnau/ISO8601/blob/b93d466840/LICENSE
   #
@@ -340,6 +355,21 @@ class DurationTest < ActiveSupport::TestCase
     end
   end
 
+  def test_iso8601_parsing_equivalence_with_numeric_extensions_over_long_periods
+    with_env_tz eastern_time_zone do
+      with_tz_default "Eastern Time (US & Canada)" do
+        assert_equal 3.months, ActiveSupport::Duration.parse("P3M")
+        assert_equal 3.months.to_i, ActiveSupport::Duration.parse("P3M").to_i
+        assert_equal 10.months, ActiveSupport::Duration.parse("P10M")
+        assert_equal 10.months.to_i, ActiveSupport::Duration.parse("P10M").to_i
+        assert_equal 3.years, ActiveSupport::Duration.parse("P3Y")
+        assert_equal 3.years.to_i, ActiveSupport::Duration.parse("P3Y").to_i
+        assert_equal 10.years, ActiveSupport::Duration.parse("P10Y")
+        assert_equal 10.years.to_i, ActiveSupport::Duration.parse("P10Y").to_i
+      end
+    end
+  end
+
   private
     def eastern_time_zone
       if Gem.win_platform?

guides/source/debugging_rails_applications.md

@@ -683,7 +683,7 @@ Ruby instruction to be executed -- in this case, Active Support's `week` method.
    51:   #
    52:   #   2.weeks # => 14 days
    53:   def weeks
-=> 54:     ActiveSupport::Duration.new(self * 7.days, [[:days, self * 7]])
+=> 54:     ActiveSupport::Duration.weeks(self)
    55:   end
    56:   alias :week :weeks
    57: