Re: [POLL] Proposed syntax for timestamps with time zone info (was: [FEATURE REQUEST] Timezone support in org-mode datestamps and org-agenda)

[Ihor Radchenko]

[ adding Org ML back to CC ]

Daryl Manning <daryl@wakatara.com> writes:

> OMG it would be amazing if (simply) going <2023-01-31 10:00 @EST> or when
> daylight savings time hits <2023-01-31 10:00 @EDT> worked.
>
> would be *super* happy with that as a user who spends a lot of time dealing
> with other time zones. =]

You can play around with the following

(format-time-string "%Y-%m-%d %a %H:%M" (current-time) "EST")
(format-time-string "%Y-%m-%d %a %H:%M" (current-time) "Asia/Singapore")

(format-time-string "%Y-%m-%d %a %H:%M" (current-time) "EDT") ; => not correct
(format-time-string "%Y-%m-%d %a %H:%M" (current-time) "EDT5") ;=> correct, 
because daylight saving is not active now

"EDT" is not supported (at least, on my system). AFAIK, the correct TZ
format is
(format-time-string "%Y-%m-%d %a %H:%M" (current-time) "EST5EDT")

(Side note: we should probably detect unsupported time zone names and
issue a warning)

Note that Emacs provides `timezone-zone-to-minute', but, as you see in
the docstring below, EST must not be used because it may be ambiguous
outside USA. (That's why POSIX TZ format demands the offset part in
addition to time zone abbreviation)

`current-time-zone' is also not helpful here:
(current-time-zone nil "EDT") ;=> (0 "EDT") == UTC??
(current-time-zone nil "EST") ;=> (-18000 "EST")
(current-time-zone nil "EST5EDT") ;=> (-18000 "EST")

(defvar timezone-world-timezones
  '(("PST" .  -800)
    ("PDT" .  -700)
    ("MST" .  -700)
    ("MDT" .  -600)
    ("CST" .  -600)
    ("CDT" .  -500)
    ("EST" .  -500)
    ("EDT" .  -400)
    ("AST" .  -400)                     ;by <clamen@CS.CMU.EDU>
    ("NST" .  -330)                     ;by <clamen@CS.CMU.EDU>
    ("UT"  .  +000)
    ("GMT" .  +000)
    ("BST" .  +100)
    ("MET" .  +100)
    ("EET" .  +200)
    ("JST" .  +900)
    ("GMT+1"  .  +100) ("GMT+2"  .  +200) ("GMT+3"  .  +300)
    ("GMT+4"  .  +400) ("GMT+5"  .  +500) ("GMT+6"  .  +600)
    ("GMT+7"  .  +700) ("GMT+8"  .  +800) ("GMT+9"  .  +900)
    ("GMT+10" . +1000) ("GMT+11" . +1100) ("GMT+12" . +1200) ("GMT+13" . +1300)
    ("GMT-1"  .  -100) ("GMT-2"  .  -200) ("GMT-3"  .  -300)
    ("GMT-4"  .  -400) ("GMT-5"  .  -500) ("GMT-6"  .  -600)
    ("GMT-7"  .  -700) ("GMT-8"  .  -800) ("GMT-9"  .  -900)
    ("GMT-10" . -1000) ("GMT-11" . -1100) ("GMT-12" . -1200))
  "Time differentials of timezone from GMT in +-HHMM form.
This list is obsolescent, and is present only for backwards compatibility,
because time zone names are ambiguous in practice.
Use `current-time-zone' instead.")

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>