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.

2 files changed, 40 insertions, 3 deletions

diff --git a/activesupport/lib/active_support/cache/mem_cache_store.rb b/activesupport/lib/active_support/cache/mem_cache_store.rb
index e09cee3335..5eee04a34e 100644
--- a/activesupport/lib/active_support/cache/mem_cache_store.rb
+++ b/activesupport/lib/active_support/cache/mem_cache_store.rb
@@ -156,7 +156,7 @@ module ActiveSupport
           expires_in = options[:expires_in].to_i
           if expires_in > 0 && !options[:raw]
             # Set the memcache expire a few minutes in the future to support race condition ttls on read
-            expires_in += 5.minutes
+            expires_in += 300
           end
           rescue_error_with false do
             @data.send(method, key, value, expires_in, options)
diff --git a/activesupport/lib/active_support/duration.rb b/activesupport/lib/active_support/duration.rb
index 70cf78519d..b92891c511 100644
--- a/activesupport/lib/active_support/duration.rb
+++ b/activesupport/lib/active_support/duration.rb
@@ -1,5 +1,7 @@
 require "active_support/core_ext/array/conversions"
 require "active_support/core_ext/object/acts_like"
+require "active_support/core_ext/string/filters"
+require "active_support/deprecation"
 
 module ActiveSupport
   # Provides accurate date and time measurements using Date#advance and
@@ -88,6 +90,25 @@ module ActiveSupport
       @parts.default = 0
     end
 
+    def coerce(other) #:nodoc:
+      ActiveSupport::Deprecation.warn(<<-MSG.squish)
+        Implicit coercion of ActiveSupport::Duration to a Numeric
+        is deprecated and will raise a TypeError in Rails 5.2.
+      MSG
+
+      [other, value]
+    end
+
+    # Compares one Duration with another or a Numeric to this Duration.
+    # Numeric values are treated as seconds.
+    def <=>(other)
+      if Duration === other
+        value <=> other.value
+      elsif Numeric === other
+        value <=> other
+      end
+    end
+
     # Adds another Duration or a Numeric to this Duration. Numeric values
     # are treated as seconds.
     def +(other)
@@ -109,6 +130,24 @@ module ActiveSupport
       self + (-other)
     end
 
+    # Multiplies this Duration by a Numeric and returns a new Duration.
+    def *(other)
+      if Numeric === other
+        Duration.new(value * other, parts.map { |type, number| [type, number * other] })
+      else
+        value * other
+      end
+    end
+
+    # Devides this Duration by a Numeric and returns a new Duration.
+    def /(other)
+      if Numeric === other
+        Duration.new(value / other, parts.map { |type, number| [type, number / other] })
+      else
+        value / other
+      end
+    end
+
     def -@ #:nodoc:
       Duration.new(-value, parts.map { |type, number| [type, -number] })
     end
@@ -212,8 +251,6 @@ module ActiveSupport
       ISO8601Serializer.new(self, precision: precision).serialize
     end
 
-    delegate :<=>, to: :value
-
     private
 
       def sum(sign, time = ::Time.current)