Deprecate implicit coercion of `ActiveSupport::Duration`

Currently `ActiveSupport::Duration` implicitly converts to a seconds
value when used in a calculation except for the explicit examples of
addition and subtraction where the duration is the receiver, e.g:

    >> 2 * 1.day
    => 172800

This results in lots of confusion especially when using durations
with dates because adding/subtracting a value from a date treats
integers as a day and not a second, e.g:

    >> Date.today
    => Wed, 01 Mar 2017
    >> Date.today + 2 * 1.day
    => Mon, 10 Apr 2490

To fix this we're implementing `coerce` so that we can provide a
deprecation warning with the intent of removing the implicit coercion
in Rails 5.2, e.g:

    >> 2 * 1.day
    DEPRECATION WARNING: Implicit coercion of ActiveSupport::Duration
    to a Numeric is deprecated and will raise a TypeError in Rails 5.2.
    => 172800

In Rails 5.2 it will raise `TypeError`, e.g:

    >> 2 * 1.day
    TypeError: ActiveSupport::Duration can't be coerced into Integer

This is the same behavior as with other types in Ruby, e.g:

    >> 2 * "foo"
    TypeError: String can't be coerced into Integer
    >> "foo" * 2
    => "foofoo"

As part of this deprecation add `*` and `/` methods to `AS::Duration`
so that calculations that keep the duration as the receiver work
correctly whether the final receiver is a `Date` or `Time`, e.g:

    >> Date.today
    => Wed, 01 Mar 2017
    >> Date.today + 1.day * 2
    => Fri, 03 Mar 2017

Fixes #27457.

1 files changed, 55 insertions, 3 deletions

diff --git a/activesupport/test/core_ext/duration_test.rb b/activesupport/test/core_ext/duration_test.rb
index 6facb04f1f..2b1a715b7a 100644
--- a/activesupport/test/core_ext/duration_test.rb
+++ b/activesupport/test/core_ext/duration_test.rb
@@ -84,8 +84,46 @@ class DurationTest < ActiveSupport::TestCase
     assert_nothing_raised { Date.today - Date.today }
   end
 
+  def test_plus
+    assert_equal 2.seconds, 1.second + 1.second
+    assert_instance_of ActiveSupport::Duration, 1.second + 1.second
+    assert_equal 2.seconds, 1.second + 1
+    assert_instance_of ActiveSupport::Duration, 1.second + 1
+  end
+
+  def test_minus
+    assert_equal 1.second, 2.seconds - 1.second
+    assert_instance_of ActiveSupport::Duration, 2.seconds - 1.second
+    assert_equal 1.second, 2.seconds - 1
+    assert_instance_of ActiveSupport::Duration, 2.seconds - 1
+  end
+
+  def test_multiply
+    assert_equal 7.days, 1.day * 7
+    assert_instance_of ActiveSupport::Duration, 1.day * 7
+
+    assert_deprecated do
+      assert_equal 86400, 1.day * 1.second
+    end
+  end
+
+  def test_divide
+    assert_equal 1.day, 7.days / 7
+    assert_instance_of ActiveSupport::Duration, 7.days / 7
+
+    assert_deprecated do
+      assert_equal 1, 1.day / 1.day
+    end
+  end
+
+  def test_date_added_with_multiplied_duration
+    assert_equal Date.civil(2017, 1, 3), Date.civil(2017, 1, 1) + 1.day * 2
+  end
+
   def test_plus_with_time
-    assert_equal 1 + 1.second, 1.second + 1, "Duration + Numeric should == Numeric + Duration"
+    assert_deprecated do
+      assert_equal 1 + 1.second, 1.second + 1, "Duration + Numeric should == Numeric + Duration"
+    end
   end
 
   def test_time_plus_duration_returns_same_time_datatype
@@ -104,6 +142,13 @@ class DurationTest < ActiveSupport::TestCase
     assert_equal 'expected a time or date, got ""', e.message, "ensure ArgumentError is not being raised by dependencies.rb"
   end
 
+  def test_implicit_coercion_is_deprecated
+    assert_deprecated { 1 + 1.second }
+    assert_deprecated { 1 - 1.second }
+    assert_deprecated { 1 * 1.second }
+    assert_deprecated { 1 / 1.second }
+  end
+
   def test_fractional_weeks
     assert_equal((86400 * 7) * 1.5, 1.5.weeks)
     assert_equal((86400 * 7) * 1.7, 1.7.weeks)
@@ -241,13 +286,20 @@ class DurationTest < ActiveSupport::TestCase
   def test_comparable
     assert_equal(-1, (0.seconds <=> 1.second))
     assert_equal(-1, (1.second <=> 1.minute))
-    assert_equal(-1, (1 <=> 1.minute))
+
+    assert_deprecated do
+      assert_equal(-1, (1 <=> 1.minute))
+    end
+
     assert_equal(0, (0.seconds <=> 0.seconds))
     assert_equal(0, (0.seconds <=> 0.minutes))
     assert_equal(0, (1.second <=> 1.second))
     assert_equal(1, (1.second <=> 0.second))
     assert_equal(1, (1.minute <=> 1.second))
-    assert_equal(1, (61 <=> 1.minute))
+
+    assert_deprecated do
+      assert_equal(1, (61 <=> 1.minute))
+    end
   end
 
   def test_twelve_months_equals_one_year