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Bug #15988

Time#dst? vs "real" timezones

Added by zverok (Victor Shepelev) about 1 year ago. Updated about 1 year ago.

Status:
Closed
Priority:
Normal
Target version:
-
[ruby-core:93557]

Description

My current timezone is Europe/Kiev.

With default zone (how it was previously):

summer = Time.new(2019, 6, 1, 14, 30, 12)  # => 2019-06-01 14:30:12 +0300 
summer.zone                                # => "EEST" 
summer.dst?                                # => true 

winter = Time.new(2019, 12, 1, 14, 30, 12) # => 2019-12-01 14:30:12 +0200 
winter.zone                                # => "EET" 
winter.dst?                                # => false 

(Note it is correctly true in summer and false in winter.)

With "real" timezone object

require 'tzinfo'
z = TZInfo::Timezone.get('Europe/Kiev')
# => #<TZInfo::DataTimezone: Europe/Kiev> 

summer = Time.new(2019, 6, 1, 14, 30, 12, z)  # => 2019-06-01 14:30:12 +0300 
summer.zone                                   # => #<TZInfo::DataTimezone: Europe/Kiev> 
summer.dst?                                   # => true 

winter = Time.new(2019, 12, 1, 14, 30, 12, z) # => 2019-12-01 14:30:12 +0200 -- offset is correct
winter.zone                                   # => #<TZInfo::DataTimezone: Europe/Kiev>
winter.dst?                                   # => true -- this is wrong!

Note that offsets are calculated correctly (+3 in summer, +2 in winter), but dst? is always true.

TZInfo itself calculates DST properly:

z.dst?(summer) # => true 
z.dst?(winter) # => false 

Seems like a serious bug to me (or at least very hard to explain behavior).

PS: With arithmetics, everything works correctly:

six_months = 6 * 30 * 24 * 60 * 60
summer + six_months                           # => 2019-11-28 13:30:12 +0200
(summer + six_months).dst?                    # => false -- that is correct

Files

time-zone-dst.patch (1.68 KB) time-zone-dst.patch jeremyevans0 (Jeremy Evans), 07/05/2019 08:56 PM

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