Add support for localized date references

Ruby's Date class automatically gives us #yesterday, #today,
and #tomorrow. And ActiveSupport has a handy Time.zone.today
for getting a localized version. But there was no localized
version of #yesterday or #tomorrow. Until now.

activesupport/CHANGELOG.md

+*   Add `Time.zone.yesterday` and `Time.zone.tomorrow`. These follow the
+    behavior of Ruby's `Date.yesterday` and `Date.tomorrow` but return localized
+    versions, similar to how `Time.zone.today` has returned a localized version
+    of `Date.today`.
+
+    *Colin Bartlett*
+
 *   Show valid keys when `assert_valid_keys` raises an exception, and show the
     wrong value as it was entered.
 

activesupport/lib/active_support/values/time_zone.rb

@@ -317,6 +317,16 @@ def today
       tzinfo.now.to_date
     end
 
+    # Returns the next date in this time zone.
+    def tomorrow
+      today + 1
+    end
+
+    # Returns the previous date in this time zone.
+    def yesterday
+      today - 1
+    end
+
     # Adjust the given time to the simultaneous time in the time zone
     # represented by +self+. Returns a Time.utc() instance -- if you want an
     # ActiveSupport::TimeWithZone instance, use Time#in_time_zone() instead.

activesupport/test/time_zone_test.rb

@@ -99,6 +99,28 @@ def test_today
     assert_equal Date.new(2000, 1, 2), ActiveSupport::TimeZone['Eastern Time (US & Canada)'].today
   end
 
+  def test_tomorrow
+    travel_to(Time.utc(2000, 1, 1, 4, 59, 59)) # 1 sec before midnight Jan 1 EST
+    assert_equal Date.new(2000, 1, 1), ActiveSupport::TimeZone['Eastern Time (US & Canada)'].tomorrow
+    travel_to(Time.utc(2000, 1, 1, 5)) # midnight Jan 1 EST
+    assert_equal Date.new(2000, 1, 2), ActiveSupport::TimeZone['Eastern Time (US & Canada)'].tomorrow
+    travel_to(Time.utc(2000, 1, 2, 4, 59, 59)) # 1 sec before midnight Jan 2 EST
+    assert_equal Date.new(2000, 1, 2), ActiveSupport::TimeZone['Eastern Time (US & Canada)'].tomorrow
+    travel_to(Time.utc(2000, 1, 2, 5)) # midnight Jan 2 EST
+    assert_equal Date.new(2000, 1, 3), ActiveSupport::TimeZone['Eastern Time (US & Canada)'].tomorrow
+  end
+
+  def test_yesterday
+    travel_to(Time.utc(2000, 1, 1, 4, 59, 59)) # 1 sec before midnight Jan 1 EST
+    assert_equal Date.new(1999, 12, 30), ActiveSupport::TimeZone['Eastern Time (US & Canada)'].yesterday
+    travel_to(Time.utc(2000, 1, 1, 5)) # midnight Jan 1 EST
+    assert_equal Date.new(1999, 12, 31), ActiveSupport::TimeZone['Eastern Time (US & Canada)'].yesterday
+    travel_to(Time.utc(2000, 1, 2, 4, 59, 59)) # 1 sec before midnight Jan 2 EST
+    assert_equal Date.new(1999, 12, 31), ActiveSupport::TimeZone['Eastern Time (US & Canada)'].yesterday
+    travel_to(Time.utc(2000, 1, 2, 5)) # midnight Jan 2 EST
+    assert_equal Date.new(2000, 1, 1), ActiveSupport::TimeZone['Eastern Time (US & Canada)'].yesterday
+  end
+
   def test_local
     time = ActiveSupport::TimeZone["Hawaii"].local(2007, 2, 5, 15, 30, 45)
     assert_equal Time.utc(2007, 2, 5, 15, 30, 45), time.time