Add compatibility for Ruby 2.4 `to_time` changes

In Ruby 2.4 the `to_time` method for both `DateTime` and `Time` will
preserve the timezone of the receiver when converting to an instance
of `Time`. Since Rails 5.0 will support Ruby 2.2, 2.3 and later we
need to introduce a compatibility layer so that apps that upgrade do
not break. New apps will have a config initializer file that defaults
to match the new Ruby 2.4 behavior going forward.

For information about the changes to Ruby see:
https://bugs.ruby-lang.org/issues/12189
https://bugs.ruby-lang.org/issues/12271

Fixes #24617.

1 files changed, 16 insertions, 0 deletions

diff --git a/activesupport/lib/active_support/core_ext/date_and_time/compatibility.rb b/activesupport/lib/active_support/core_ext/date_and_time/compatibility.rb
new file mode 100644
index 0000000000..b8eb587390
--- /dev/null
+++ b/activesupport/lib/active_support/core_ext/date_and_time/compatibility.rb
@@ -0,0 +1,16 @@
+module DateAndTime
+  module Compatibility
+    # If true, +to_time+ preserves the the timezone offset.
+    #
+    # NOTE: With Ruby 2.4+ the default for +to_time+ changed from
+    # converting to the local system time to preserving the offset
+    # of the receiver. For backwards compatibility we're overriding
+    # this behavior but new apps will have an initializer that sets
+    # this to true because the new behavior is preferred.
+    mattr_accessor(:preserve_timezone, instance_writer: false) { false }
+
+    def to_time
+      preserve_timezone ? getlocal(utc_offset) : getlocal
+    end
+  end
+end