TZInfo with ActiveSupport - Samoa Timezone error

[pedrofurtado]

I am having the same issue as this user, that created this issue in repository of Rails: (rails/rails#27419)

Steps to reproduce

In rails console.

DateTime.now.in_time_zone("Samoa") Returns a date with a UTC offset of + 14:00
ActiveSupport::TimeZone.new('Samoa').utc_offset/60/60 Returns -11

Expected behavior

ActiveSupport::TimeZone.new('Samoa').utc_offset/60/60 Should return 14 or 13 based on daylight savings time

Actual behavior

ActiveSupport::TimeZone.new('Samoa').utc_offset/60/60 Returns -11

System configuration

Rails version: 5.0.2

Ruby version: 2.3.3

[philr]

It looks like there is a bug with the TZInfo zoneinfo data source that is causing the Pacific/Apia time zone (that Active Support calls Samoa) to be represented with a base offset of -11 hours and a daylight savings offset of either +24 or +25 hours (instead of a base offset of +13 hours and a daylight savings offset of either 0 or +1 hour):

require 'tzinfo'
TZInfo::DataSource.set(:zoneinfo)
period = TZInfo::Timezone.get('Pacific/Apia').period_for_utc(Time.utc(2017, 3, 6))
period.utc_offset / 3600       # => -11
period.std_offset / 3600       # =>  25 
period.utc_total_offset / 3600 # =>  14

The reason for the difference between DateTime.now.in_time_zone("Samoa") and ActiveSupport::TimeZone.new('Samoa').utc_offset/60/60 is that the former is showing the offset including daylight savings time (utc_total_offset) and the latter is returning just the base offset (utc_offset).

The expected behaviour is that ActiveSupport::TimeZone.new('Samoa').utc_offset/60/60 would always return 13 regardless of whether daylight savings time is being observed.

Pacific/Apia switched from one side of the International Date Line to the other in December 2011. I suspect that the code that attempts to derive the daylight savings offset from zoneinfo files is not handling this change correctly.

I'll look into fixing the bug. In the mean time, you can work around the problem by using the tzinfo-data gem as TZInfo's data source instead of the system zoneinfo files.

require 'tzinfo'
TZInfo::DataSource.set(:ruby)
period = TZInfo::Timezone.get('Pacific/Apia').period_for_utc(Time.utc(2017, 3, 6))
period.utc_offset / 3600       # => 13
period.std_offset / 3600       # =>  1 
period.utc_total_offset / 3600 # => 14

To change the data source, you'll need to add a dependency on tzinfo-data to your Gemfile. By default, Rails ships with this dependency, but limits it to Windows and JRuby. You'll either need to remove the platforms: option from the existing gem 'tzinfo-data' line if it is there, or add gem 'tzinfo-data' to the Gemfile.

[pedrofurtado]

Thanks @philr !

[philr]

The fix for this issue has now been released in version 1.2.3.