Time Zones say WHA?

gistfile1.txt

$ rails -v
Rails 3.2.8
$ rails c
Loading development environment (Rails 3.2.8)
1.9.3-p194 :001 > Time.zone = 'Paris'
 => "Paris" 
1.9.3-p194 :002 > t = Time.zone
 => (GMT+01:00) Paris # HUH?  Paris is GMT+02:00 right now, thanks to DST

Now deep in the bowels of ActiveSupport::TimeZone, we have the following:

def utc_offset                                                              
  if @utc_offset                                                            
    @utc_offset                                                             
  else                                                                      
    @current_period ||= tzinfo.try(:current_period)                         
    @current_period.try(:utc_offset)                                        
  end                                                                       
end

Now, TZInfo has a fancy method called utc_total_offset that, according to the docs, does the following:
utc_total_offset() - Total offset from UTC (seconds). Equal to utc_offset + std_offset.

A HA!  std_offset?  As in, an offset that's added to the utc_offset when a time zone is in DST?

When we patch this ActiveSupport method to use utc_total_offset instead of the dumber utc_offset, we get the following:

$ rails c
Loading development environment (Rails 3.2.8)
1.9.3-p194 :001 > Time.zone = 'Paris'
 => "Paris" 
1.9.3-p194 :002 > t = Time.zone
 => (GMT+02:00) Paris # HUZZAH!!!!

Try typing:

[11] pry(main)> Time.zone.now
=> Tue, 02 Oct 2012 05:43:25 CEST +02:00

Note that it gives you the 2 hour offset.

I think that is stores the zone w/o DST context so that it can be persisted. Then calculates the correct offset at the time of evaluation to ensure it is accurate when needed.

Imagine an application that was up and running at the time that DST took affect. It would need to calculate the offset at the time of evaluation, not the time that it was set/stored.

Disclaimer: this is more conjecture than tracing code/digging into AS, but I think the evaluation of the current time strongly supports this theory.

You're exactly right :).

The calculations are correct - it's purely a display issue. But it's a pretty lousy one - in our time zone picker, the value you select is Paris (GMT+01:00) but Rails saves any datetime in that timezone as GMT+2 :/