Make Time#change work with offsets other than UTC or local

Use Time.new to create times where the current offset is not zero or
not in the local time zone - closes rails#4847 and rails#6651.

activesupport/CHANGELOG.md

@@ -1,5 +1,7 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Time#change now works with time values with offsets other than UTC or the local time zone. *Andrew White*
+
 *   AS::Callbacks: deprecate usage of filter object with `#before` and `#after` methods as `around` callback. *Bogdan Gusiev*
 
 *   Add `Time#prev_quarter' and 'Time#next_quarter' short-hands for months_ago(3) and months_since(3). *SungHee Kang*

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

@@ -86,16 +86,21 @@ def seconds_since_midnight
   # (hour, min, sec, usec) reset cascadingly, so if only the hour is passed, then minute, sec, and usec is set to 0. If the hour and
   # minute is passed, then sec and usec is set to 0.
   def change(options)
-    ::Time.send(
-      utc? ? :utc_time : :local_time,
-      options.fetch(:year, year),
-      options.fetch(:month, month),
-      options.fetch(:day, day),
-      options.fetch(:hour, hour),
-      options.fetch(:min, options[:hour] ? 0 : min),
-      options.fetch(:sec, (options[:hour] || options[:min]) ? 0 : sec),
-      options.fetch(:usec, (options[:hour] || options[:min] || options[:sec]) ? 0 : Rational(nsec, 1000))
-    )
+    new_year  = options.fetch(:year, year)
+    new_month = options.fetch(:month, month)
+    new_day   = options.fetch(:day, day)
+    new_hour  = options.fetch(:hour, hour)
+    new_min   = options.fetch(:min, options[:hour] ? 0 : min)
+    new_sec   = options.fetch(:sec, (options[:hour] || options[:min]) ? 0 : sec)
+    new_usec  = options.fetch(:usec, (options[:hour] || options[:min] || options[:sec]) ? 0 : Rational(nsec, 1000))
+
+    if utc?
+      ::Time.utc(new_year, new_month, new_day, new_hour, new_min, new_sec, new_usec)
+    elsif zone
+      ::Time.local(new_year, new_month, new_day, new_hour, new_min, new_sec, new_usec)
+    else
+      ::Time.new(new_year, new_month, new_day, new_hour, new_min, new_sec + (new_usec.to_r / 1000000), utc_offset)
+    end
   end
 
   # Uses Date to provide precise Time calculations for years, months, and days.

activesupport/test/core_ext/time_ext_test.rb

@@ -459,6 +459,15 @@ def test_utc_change
     assert_equal Time.utc(2005,2,22,15,45),    Time.utc(2005,2,22,15,15,10).change(:min => 45)
   end
 
+  def test_offset_change
+    assert_equal Time.new(2006,2,22,15,15,10,"-08:00"), Time.new(2005,2,22,15,15,10,"-08:00").change(:year => 2006)
+    assert_equal Time.new(2005,6,22,15,15,10,"-08:00"), Time.new(2005,2,22,15,15,10,"-08:00").change(:month => 6)
+    assert_equal Time.new(2012,9,22,15,15,10,"-08:00"), Time.new(2005,2,22,15,15,10,"-08:00").change(:year => 2012, :month => 9)
+    assert_equal Time.new(2005,2,22,16,0,0,"-08:00"),   Time.new(2005,2,22,15,15,10,"-08:00").change(:hour => 16)
+    assert_equal Time.new(2005,2,22,16,45,0,"-08:00"),  Time.new(2005,2,22,15,15,10,"-08:00").change(:hour => 16, :min => 45)
+    assert_equal Time.new(2005,2,22,15,45,0,"-08:00"),  Time.new(2005,2,22,15,15,10,"-08:00").change(:min => 45)
+  end
+
   def test_advance
     assert_equal Time.local(2006,2,28,15,15,10), Time.local(2005,2,28,15,15,10).advance(:years => 1)
     assert_equal Time.local(2005,6,28,15,15,10), Time.local(2005,2,28,15,15,10).advance(:months => 4)
@@ -503,6 +512,28 @@ def test_utc_advance
     assert_equal Time.utc(2013,10,17,20,22,19), Time.utc(2005,2,28,15,15,10).advance(:years => 7, :months => 19, :weeks => 2, :days => 5, :hours => 5, :minutes => 7, :seconds => 9)
   end
 
+  def test_offset_advance
+    assert_equal Time.new(2006,2,22,15,15,10,'-08:00'), Time.new(2005,2,22,15,15,10,'-08:00').advance(:years => 1)
+    assert_equal Time.new(2005,6,22,15,15,10,'-08:00'), Time.new(2005,2,22,15,15,10,'-08:00').advance(:months => 4)
+    assert_equal Time.new(2005,3,21,15,15,10,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:weeks => 3)
+    assert_equal Time.new(2005,3,25,3,15,10,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:weeks => 3.5)
+    assert_in_delta Time.new(2005,3,26,12,51,10,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:weeks => 3.7), 1
+    assert_equal Time.new(2005,3,5,15,15,10,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:days => 5)
+    assert_equal Time.new(2005,3,6,3,15,10,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:days => 5.5)
+    assert_in_delta Time.new(2005,3,6,8,3,10,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:days => 5.7), 1
+    assert_equal Time.new(2012,9,22,15,15,10,'-08:00'), Time.new(2005,2,22,15,15,10,'-08:00').advance(:years => 7, :months => 7)
+    assert_equal Time.new(2013,10,3,15,15,10,'-08:00'), Time.new(2005,2,22,15,15,10,'-08:00').advance(:years => 7, :months => 19, :days => 11)
+    assert_equal Time.new(2013,10,17,15,15,10,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:years => 7, :months => 19, :weeks => 2, :days => 5)
+    assert_equal Time.new(2001,12,27,15,15,10,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:years => -3, :months => -2, :days => -1)
+    assert_equal Time.new(2005,2,28,15,15,10,'-08:00'), Time.new(2004,2,29,15,15,10,'-08:00').advance(:years => 1) #leap day plus one year
+    assert_equal Time.new(2005,2,28,20,15,10,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:hours => 5)
+    assert_equal Time.new(2005,2,28,15,22,10,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:minutes => 7)
+    assert_equal Time.new(2005,2,28,15,15,19,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:seconds => 9)
+    assert_equal Time.new(2005,2,28,20,22,19,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:hours => 5, :minutes => 7, :seconds => 9)
+    assert_equal Time.new(2005,2,28,10,8,1,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:hours => -5, :minutes => -7, :seconds => -9)
+    assert_equal Time.new(2013,10,17,20,22,19,'-08:00'), Time.new(2005,2,28,15,15,10,'-08:00').advance(:years => 7, :months => 19, :weeks => 2, :days => 5, :hours => 5, :minutes => 7, :seconds => 9)
+  end
+
   def test_advance_with_nsec
     t = Time.at(0, Rational(108635108, 1000))
     assert_equal t, t.advance(:months => 0)