Add ActiveSupport::TimeZone#dst?

Like abbr, this is used by Ruby when specifying creating a ::Time with a
zone object.

Author: jhawthorn

activesupport/lib/active_support/values/time_zone.rb

@@ -574,6 +574,12 @@ def abbr(time)
       tzinfo.abbr(time)
     end
 
+    # Available so that TimeZone instances respond like +TZInfo::Timezone+
+    # instances.
+    def dst?(time)
+      tzinfo.dst?(time)
+    end
+
     def init_with(coder) # :nodoc:
       initialize(coder["name"])
     end

activesupport/test/time_zone_test.rb

@@ -886,4 +886,38 @@ def test_abbr
     assert_equal "EST", zone.abbr(Time.utc(2000, 10, 29, 6))
     assert_equal "EST", zone.abbr(Time.utc(2000, 10, 29, 7))
   end
+
+  def test_dst
+    zone = ActiveSupport::TimeZone["America/Toronto"]
+    assert_equal false, zone.dst?(Time.utc(2000, 4, 2, 6))
+    assert_equal true,  zone.dst?(Time.utc(2000, 4, 2, 7))
+    assert_equal true,  zone.dst?(Time.utc(2000, 4, 2, 8))
+    assert_equal true,  zone.dst?(Time.utc(2000, 10, 29, 5))
+    assert_equal false, zone.dst?(Time.utc(2000, 10, 29, 6))
+    assert_equal false, zone.dst?(Time.utc(2000, 10, 29, 7))
+  end
+
+  def test_works_as_ruby_time_zone
+    zone = ActiveSupport::TimeZone["America/Toronto"]
+    time = Time.new(2000, 1, 1, 1, in: zone)
+    assert_same zone, time.zone
+    assert_equal "2000-01-01T01:00:00-05:00", time.iso8601
+    assert_equal(-18000, time.utc_offset)
+    assert_equal "EST", time.strftime("%Z")
+    assert_equal false, time.isdst
+
+    time = Time.new(2000, 6, 1, 1, in: zone)
+    assert_same zone, time.zone
+    assert_equal "2000-06-01T01:00:00-04:00", time.iso8601
+    assert_equal(-14400, time.utc_offset)
+    assert_equal "EDT", time.strftime("%Z")
+    assert_equal true, time.isdst
+
+    time = Time.at(959835600, in: zone)
+    assert_same zone, time.zone
+    assert_equal "2000-06-01T01:00:00-04:00", time.iso8601
+    assert_equal(-14400, time.utc_offset)
+    assert_equal "EDT", time.strftime("%Z")
+    assert_equal true, time.isdst
+  end
 end