Time#- with a DateTime argument behaves the same as with a Time argum…

…ent, i.e. returns the difference between self and arg as a Float [#3476 status:resolved]

activesupport/CHANGELOG

@@ -1,5 +1,7 @@
 *2.3.6 (pending)*
 
+* Time#- with a DateTime argument behaves the same as with a Time argument, i.e. returns the difference between self and arg as a Float #3476 [Geoff Buesing]
+
 * YAML serialization for OrderedHash.  #3608 [Gregor Schmidt]
 
 * Update bundled TZInfo to v0.3.16 [Geoff Buesing]

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

@@ -283,7 +283,7 @@ def minus_with_duration(other) #:nodoc:
         # are coerced into values that Time#- will recognize
         def minus_with_coercion(other)
           other = other.comparable_time if other.respond_to?(:comparable_time)
-          minus_without_coercion(other)
+          other.is_a?(::DateTime) ? to_f - other.to_f : minus_without_coercion(other)
         end
 
         # Layers additional behavior on Time#<=> so that DateTime and ActiveSupport::TimeWithZone instances

activesupport/test/core_ext/time_ext_test.rb

@@ -680,6 +680,10 @@ def test_compare_with_time_with_zone
   def test_minus_with_time_with_zone
     assert_equal  86_400.0, Time.utc(2000, 1, 2) - ActiveSupport::TimeWithZone.new( Time.utc(2000, 1, 1), ActiveSupport::TimeZone['UTC'] )
   end
+
+  def test_minus_with_datetime
+    assert_equal  86_400.0, Time.utc(2000, 1, 2) - DateTime.civil(2000, 1, 1)
+  end
 
   def test_time_created_with_local_constructor_cannot_represent_times_during_hour_skipped_by_dst
     with_env_tz 'US/Eastern' do