Override Time.at to work with Time-like values

Time.at allows passing a single Time argument which is then converted
to an integer. The conversion code since 1.9.3r429 explicitly checks
for an instance of Time so we need to override it to allow DateTime
and ActiveSupport::TimeWithZone values.

activesupport/CHANGELOG.md

+*   Override `Time.at` to support the passing of Time-like values when called with a single argument.
+
+    *Andrew White*
+
 *   Prevent side effects to hashes inside arrays when
     `Hash#with_indifferent_access` is called.
     Fixes #10526

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

@@ -65,6 +65,18 @@ def local_time(*args)
     def current
       ::Time.zone ? ::Time.zone.now : ::Time.now
     end
+
+    # Layers additional behavior on Time.at so that ActiveSupport::TimeWithZone and DateTime
+    # instances can be used when called with a single argument
+    def at_with_coercion(*args)
+      if args.size == 1 && args.first.acts_like?(:time)
+        at_without_coercion(args.first.to_i)
+      else
+        at_without_coercion(*args)
+      end
+    end
+    alias_method :at_without_coercion, :at
+    alias_method :at, :at_with_coercion
   end
 
   # Seconds since midnight: Time.now.seconds_since_midnight

activesupport/test/core_ext/time_ext_test.rb

@@ -741,6 +741,28 @@ def test_compare_with_time_with_zone
     assert_equal(-1, Time.utc(2000) <=> ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 1, 0, 0, 1), ActiveSupport::TimeZone['UTC'] ))
   end
 
+  def test_at_with_datetime
+    assert_equal Time.utc(2000, 1, 1, 0, 0, 0), Time.at(DateTime.civil(2000, 1, 1, 0, 0, 0))
+
+    # Only test this if the underlying Time.at raises a TypeError
+    begin
+      Time.at_without_coercion(Time.now, 0)
+    rescue TypeError
+      assert_raise(TypeError) { assert_equal(Time.utc(2000, 1, 1, 0, 0, 0), Time.at(DateTime.civil(2000, 1, 1, 0, 0, 0), 0)) }
+    end
+  end
+
+  def test_at_with_time_with_zone
+    assert_equal Time.utc(2000, 1, 1, 0, 0, 0), Time.at(ActiveSupport::TimeWithZone.new(Time.utc(2000, 1, 1, 0, 0, 0), ActiveSupport::TimeZone['UTC']))
+
+    # Only test this if the underlying Time.at raises a TypeError
+    begin
+      Time.at_without_coercion(Time.now, 0)
+    rescue TypeError
+      assert_raise(TypeError) { assert_equal(Time.utc(2000, 1, 1, 0, 0, 0), Time.at(ActiveSupport::TimeWithZone.new(Time.utc(2000, 1, 1, 0, 0, 0), ActiveSupport::TimeZone['UTC']), 0)) }
+    end
+  end
+
   def test_eql?
     assert_equal true, Time.utc(2000).eql?( ActiveSupport::TimeWithZone.new(Time.utc(2000), ActiveSupport::TimeZone['UTC']) )
     assert_equal true, Time.utc(2000).eql?( ActiveSupport::TimeWithZone.new(Time.utc(2000), ActiveSupport::TimeZone["Hawaii"]) )