Fix `ActiveSupport::TimeZone#strptime` cannot parse timestamps (%Q, %s)

activesupport/CHANGELOG.md

+*   Fix `ActiveSupport::TimeZone#strptime`.
+    Support for timestamps in format of seconds (%s) and milliseconds (%Q).
+
+    Fixes #26840.
+
+    *Lev Denisov*
+
 *   Fix `DateAndTime::Calculations#copy_time_to`. Copy `nsec` instead of `usec`.
 
     Jumping forward or backward between weeks now preserves nanosecond digits.

activesupport/lib/active_support/values/time_zone.rb

@@ -450,17 +450,21 @@ def parts_to_time(parts, now)
         raise ArgumentError, "invalid date" if parts.nil?
         return if parts.empty?
 
-        time = Time.new(
-          parts.fetch(:year, now.year),
-          parts.fetch(:mon, now.month),
-          parts.fetch(:mday, parts[:year] || parts[:mon] ? 1 : now.day),
-          parts.fetch(:hour, 0),
-          parts.fetch(:min, 0),
-          parts.fetch(:sec, 0) + parts.fetch(:sec_fraction, 0),
-          parts.fetch(:offset, 0)
-        )
-
-        if parts[:offset]
+        if parts[:seconds]
+          time = Time.at(parts[:seconds])
+        else
+          time = Time.new(
+            parts.fetch(:year, now.year),
+            parts.fetch(:mon, now.month),
+            parts.fetch(:mday, parts[:year] || parts[:mon] ? 1 : now.day),
+            parts.fetch(:hour, 0),
+            parts.fetch(:min, 0),
+            parts.fetch(:sec, 0) + parts.fetch(:sec_fraction, 0),
+            parts.fetch(:offset, 0)
+          )
+        end
+
+        if parts[:offset] || parts[:seconds]
           TimeWithZone.new(time.utc, self)
         else
           TimeWithZone.new(nil, self, time)

activesupport/test/time_zone_test.rb

@@ -395,6 +395,24 @@ def test_strptime_with_malformed_string
     end
   end
 
+  def test_strptime_with_timestamp_seconds
+    with_env_tz "US/Eastern" do
+      zone = ActiveSupport::TimeZone["Eastern Time (US & Canada)"]
+      time_str = "1470272280"
+      time = zone.strptime(time_str, "%s")
+      assert_equal Time.at(1470272280), time
+    end
+  end
+
+  def test_strptime_with_timestamp_milliseconds
+    with_env_tz "US/Eastern" do
+      zone = ActiveSupport::TimeZone["Eastern Time (US & Canada)"]
+      time_str = "1470272280000"
+      time = zone.strptime(time_str, "%Q")
+      assert_equal Time.at(1470272280), time
+    end
+  end
+
   def test_utc_offset_lazy_loaded_from_tzinfo_when_not_passed_in_to_initialize
     tzinfo = TZInfo::Timezone.get("America/New_York")
     zone = ActiveSupport::TimeZone.create(tzinfo.name, nil, tzinfo)