Ensure duration parsing is consistent across DST changes
Previously `ActiveSupport::Duration.parse` used `Time.current` and `Time#advance` to calculate the number of seconds in the duration from an arbitrary collection of parts. However as `advance` tries to be consistent across DST boundaries this meant that either the duration was shorter or longer depending on the time of year. This was fixed by using an absolute reference point in UTC which isn't subject to DST transitions. An arbitrary date of Jan 1st, 2000 was chosen for no other reason that it seemed appropriate. Additionally, duration parsing should now be marginally faster as we are no longer creating instances of `ActiveSupport::TimeWithZone` every time we parse a duration string. Fixes #26941.
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@ -1,3 +1,23 @@
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* Ensure duration parsing is consistent across DST changes
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Previously `ActiveSupport::Duration.parse` used `Time.current` and
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`Time#advance` to calculate the number of seconds in the duration
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from an arbitrary collection of parts. However as `advance` tries to
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be consistent across DST boundaries this meant that either the
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duration was shorter or longer depending on the time of year.
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This was fixed by using an absolute reference point in UTC which
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isn't subject to DST transitions. An arbitrary date of Jan 1st, 2000
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was chosen for no other reason that it seemed appropriate.
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Additionally, duration parsing should now be marginally faster as we
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are no longer creating instances of `ActiveSupport::TimeWithZone`
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every time we parse a duration string.
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Fixes #26941.
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*Andrew White*
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* Use `Hash#compact` and `Hash#compact!` from Ruby 2.4. Old Ruby versions
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will continue to get these methods from Active Support as before.
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@ -7,6 +7,8 @@ module ActiveSupport
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#
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# 1.month.ago # equivalent to Time.now.advance(months: -1)
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class Duration
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EPOCH = ::Time.utc(2000)
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attr_accessor :value, :parts
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autoload :ISO8601Parser, "active_support/duration/iso8601_parser"
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@ -140,8 +142,7 @@ def respond_to_missing?(method, include_private = false) #:nodoc:
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# If invalid string is provided, it will raise +ActiveSupport::Duration::ISO8601Parser::ParsingError+.
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def self.parse(iso8601duration)
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parts = ISO8601Parser.new(iso8601duration).parse!
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time = ::Time.current
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new(time.advance(parts) - time, parts)
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new(EPOCH.advance(parts) - EPOCH, parts)
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end
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# Build ISO 8601 Duration string for this duration.
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@ -322,4 +322,35 @@ def test_iso8601_output_and_reparsing
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assert_equal time + duration, time + ActiveSupport::Duration.parse(duration.iso8601), pattern.inspect
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end
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end
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def test_iso8601_parsing_across_spring_dst_boundary
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with_env_tz eastern_time_zone do
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with_tz_default "Eastern Time (US & Canada)" do
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travel_to Time.utc(2016, 3, 11) do
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assert_equal 604800, ActiveSupport::Duration.parse("P7D").to_i
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assert_equal 604800, ActiveSupport::Duration.parse("P1W").to_i
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end
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end
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end
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end
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def test_iso8601_parsing_across_autumn_dst_boundary
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with_env_tz eastern_time_zone do
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with_tz_default "Eastern Time (US & Canada)" do
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travel_to Time.utc(2016, 11, 4) do
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assert_equal 604800, ActiveSupport::Duration.parse("P7D").to_i
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assert_equal 604800, ActiveSupport::Duration.parse("P1W").to_i
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end
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end
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end
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end
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private
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def eastern_time_zone
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if Gem.win_platform?
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"EST5EDT"
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else
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"America/New_York"
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end
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end
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end
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