Add :weeks to the list of variable duration parts

Since 434df00 week durations are no longer converted to days. This means
we need to add :weeks to the parts that ActiveSupport::TimeWithZone will
consider being of variable duration to take account of DST transitions.

Fixes #26039.

activesupport/CHANGELOG.md

@@ -1,3 +1,11 @@
+*   Since weeks are no longer converted to days, add `:weeks` to the list of
+    parts that `ActiveSupport::TimeWithZone` will recognize as possibly being
+    of variable duration to take account of DST transitions.
+
+    Fixes #26039.
+
+    *Andrew White*
+
 *   Defines `Regexp.match?` for Ruby versions prior to 2.4. The predicate
     has the same interface, but it does not have the performance boost. Its
     purpose is to be able to write 2.4 compatible code.

activesupport/lib/active_support/time_with_zone.rb

@@ -481,7 +481,7 @@ module ActiveSupport
       end
 
       def duration_of_variable_length?(obj)
-        ActiveSupport::Duration === obj && obj.parts.any? {|p| [:years, :months, :days].include?(p[0]) }
+        ActiveSupport::Duration === obj && obj.parts.any? {|p| [:years, :months, :weeks, :days].include?(p[0]) }
       end
 
       def wrap_with_time_zone(time)

activesupport/test/core_ext/time_with_zone_test.rb

@@ -834,6 +834,38 @@ class TimeWithZoneTest < ActiveSupport::TestCase
     assert_equal "Sat, 28 Oct 2006 10:30:00 EDT -04:00", twz.advance(:hours => -24).inspect
   end
 
+  def test_advance_1_week_across_spring_dst_transition
+    twz = ActiveSupport::TimeWithZone.new(nil, @time_zone, Time.utc(2006,4,1,10,30))
+    assert_equal "Sat, 08 Apr 2006 10:30:00 EDT -04:00", twz.advance(:weeks => 1).inspect
+    assert_equal "Sat, 08 Apr 2006 10:30:00 EDT -04:00", twz.weeks_since(1).inspect
+    assert_equal "Sat, 08 Apr 2006 10:30:00 EDT -04:00", twz.since(1.week).inspect
+    assert_equal "Sat, 08 Apr 2006 10:30:00 EDT -04:00", (twz + 1.week).inspect
+  end
+
+  def test_advance_1_week_across_spring_dst_transition_backwards
+    twz = ActiveSupport::TimeWithZone.new(nil, @time_zone, Time.utc(2006,4,8,10,30))
+    assert_equal "Sat, 01 Apr 2006 10:30:00 EST -05:00", twz.advance(:weeks => -1).inspect
+    assert_equal "Sat, 01 Apr 2006 10:30:00 EST -05:00", twz.weeks_ago(1).inspect
+    assert_equal "Sat, 01 Apr 2006 10:30:00 EST -05:00", twz.ago(1.week).inspect
+    assert_equal "Sat, 01 Apr 2006 10:30:00 EST -05:00", (twz - 1.week).inspect
+  end
+
+  def test_advance_1_week_across_fall_dst_transition
+    twz = ActiveSupport::TimeWithZone.new(nil, @time_zone, Time.utc(2006,10,28,10,30))
+    assert_equal "Sat, 04 Nov 2006 10:30:00 EST -05:00", twz.advance(:weeks => 1).inspect
+    assert_equal "Sat, 04 Nov 2006 10:30:00 EST -05:00", twz.weeks_since(1).inspect
+    assert_equal "Sat, 04 Nov 2006 10:30:00 EST -05:00", twz.since(1.week).inspect
+    assert_equal "Sat, 04 Nov 2006 10:30:00 EST -05:00", (twz + 1.week).inspect
+  end
+
+  def test_advance_1_week_across_fall_dst_transition_backwards
+    twz = ActiveSupport::TimeWithZone.new(nil, @time_zone, Time.utc(2006,11,4,10,30))
+    assert_equal "Sat, 28 Oct 2006 10:30:00 EDT -04:00", twz.advance(:weeks => -1).inspect
+    assert_equal "Sat, 28 Oct 2006 10:30:00 EDT -04:00", twz.weeks_ago(1).inspect
+    assert_equal "Sat, 28 Oct 2006 10:30:00 EDT -04:00", twz.ago(1.week).inspect
+    assert_equal "Sat, 28 Oct 2006 10:30:00 EDT -04:00", (twz - 1.week).inspect
+  end
+
   def test_advance_1_month_across_spring_dst_transition
     twz = ActiveSupport::TimeWithZone.new(nil, @time_zone, Time.utc(2006,4,1,10,30))
     assert_equal "Mon, 01 May 2006 10:30:00 EDT -04:00", twz.advance(:months => 1).inspect