Standardise the return value of `to_time`

This commit standardises the return value of `to_time` to an instance
of `Time` in the local system timezone, matching the Ruby core and
standard library behavior.

The default form for `String#to_time` has been changed from :utc to
:local but research seems to suggest the latter is the more common form.

Also fix an edge condition with `String#to_time` where the string has
a timezone offset in it and the mode is :local. e.g:

  # Before:
  >> "2000-01-01 00:00:00 -0500".to_time(:local)
  => 2000-01-01 05:00:00 -0500

  # After:
  >> "2000-01-01 00:00:00 -0500".to_time(:local)
  => 2000-01-01 00:00:00 -0500

Closes #2453

1 files changed, 5 insertions, 1 deletions

diff --git a/activesupport/CHANGELOG.md b/activesupport/CHANGELOG.md
index 2c0d1de70f..72f28aefc7 100644
--- a/activesupport/CHANGELOG.md
+++ b/activesupport/CHANGELOG.md
@@ -1,5 +1,10 @@
 ## Rails 4.0.0 (unreleased) ##
 
+*   Standardise on `to_time` returning an instance of `Time` in the local system timezone
+    across `String`, `Time`, `Date`, `DateTime` and `ActiveSupport::TimeWithZone`.
+
+    *Andrew White*
+
 *   Extract `ActiveSupport::Testing::Performance` into https://github.com/rails/rails-perftest
     You can add the gem to your Gemfile to keep using performance tests.
 
@@ -7,7 +12,6 @@
 
     *Yves Senn*
 
-
 *   Hash.from_xml raises when it encounters type="symbol" or type="yaml".
     Use Hash.from_trusted_xml to parse this XML.