[tz] Incorrect Time Zone Data for American/Grand_Turk

[Brian Inglis]

On 2018-07-23 10:48, Robert MacGrogan wrote:
> It looks to me like the time zone data for America/Grand_Turk is incorrect
> in 2018e version of the database. Turks and Caicos switched to supporting
> daylight savings time in March of 2018. So in summer the correct time for 
> America/Ground_Turk should be GMT -4 and then back to GMT -5 again in the
> fall.
> 
> The current database returns times for summer of 2018 as GMT -5, which is 
> incorrect.

Your installed time zone data may be incorrect but 2018e is correct:

$ TZ=America/Grand_Turk date +%c%z%Z
2018 Jul 24 Tue 10:31:25-0400EDT

$ apt list tzdata
tzdata 2018e-1 x86_64 [installed, automatic]

and has not changed since the TCI announcement in 2017, updated in 2017c,
generated on Oct 20, released on Oct 23 (boy, was last year controlled?):

$ head -20 tz/releases/tzdata2017c/NEWS
News for the tz database

Release 2017c - 2017-10-20 14:49:34 -0700

  Briefly:
  Northern Cyprus switches from +03 to +02/+03 on 2017-10-29.
  Fiji ends DST 2018-01-14, not 2018-01-21.
  Namibia switches from +01/+02 to +02 on 2018-04-01.
  Sudan switches from +03 to +02 on 2017-11-01.
  Tonga likely switches from +13/+14 to +13 on 2017-11-05.
  Turks & Caicos switches from -04 to -05/-04 on 2018-11-04.
...

when northamerica was changed:

# From the Turks & Caicos Cabinet (2017-07-20), heads-up from Steffen Thorsen:
# ... agreed to the reintroduction in TCI of Daylight Saving Time (DST)
# during the summer months and Standard Time, also known as Local
# Time, during the winter months with effect from April 2018 ...
#
https://www.gov.uk/government/news/turks-and-caicos-post-cabinet-meeting-statement--3
#
# From Paul Eggert (2017-08-26):
# The date of effect of the spring 2018 change appears to be March 11,
# which makes more sense.  See: Hamilton D. Time change back
# by March 2018 for TCI. Magnetic Media. 2017-08-25.
# http://magneticmediatv.com/2017/08/time-change-back-by-march-2018-for-tci/
#
# Zone  NAME            GMTOFF  RULES   FORMAT  [UNTIL]
Zone America/Grand_Turk -4:44:32 -      LMT     1890
                        -5:07:10 -      KMT     1912 Feb # Kingston Mean Time
                        -5:00   -       EST     1979
                        -5:00   US      E%sT    2015 Nov Sun>=1 2:00
                        -4:00   -       AST     2018 Mar 11 3:00
                        -5:00   US      E%sT

which shows EST between 1912-1979, EST/EDT until 2015, rezone and stay on AST
until 2018, then back to EDT/EST on US rules.

-- 
Take care. Thanks, Brian Inglis, Calgary, Alberta, Canada