Active Support time zone offset

[gabriel-curtino]

ActiveSupport and TZInfo utc_offset return different values. TZinfo gives the correct current offset value (EDT UTC-4h) for today.

Expected behavior

#> Time.find_zone("America/New_York").utc_offset
=> -14400 # -04:00
#> Time.find_zone("America/New_York").tzinfo.utc_offset
=> -14400 # -04:00

Actual behavior

#> Time.find_zone("America/New_York").utc_offset
=> -18000 # -05:00
#> Time.find_zone("America/New_York").tzinfo.utc_offset
=> -14400 # -04:00

System configuration

Rails version: 6.1.3.2
Ruby version: 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-linux]

[airled]

#42467 Related?

[gabriel-curtino]

#42467 Related?

I don't think so... it doesn't seems just a daylight savings difference there.

[gabriel-curtino]

rails/activesupport/lib/active_support/values/time_zone.rb

Line 285 in f626b47

tzinfo.current_period.utc_offset if tzinfo && tzinfo.current_period

Find out that ActiveSupport::Timezone.utc_offset comes form TZInfo::TimezonePeriod.utc_offset that says (2):

Returns the base offset from UTC in seconds (observed_utc_offset - std_offset). This does not include any adjustment made for daylight savings time and will typically remain constant throughout the year.

To obtain the currently observed offset from UTC, including the effect of daylight savings time, use #observed_utc_offset instead.

I'm expecting to get the current offset because I'm creating a DateTime in an specific timezone but got it wrong. It has not to be like I was expecting although I think it makes more sense to retrieve the current offset or at least document that ActiveSupport::Timezone.utc_offset retrieves the "base" offset... and maybe a new method to get the current one?

Well, I don't think anymore this is a bug.

(2) https://rubydoc.info/gems/tzinfo/TZInfo/TimezonePeriod#base_utc_offset-instance_method