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

[Ihor Radchenko]

Jean Louis <bugs@gnu.support> writes:

> * Ihor Radchenko <yantar92@posteo.net> [2023-02-05 13:45]:
>> [2024-02-04 12:00 @-08,America/Vancouver] will use fixed -8 offset
>
> What does that mean practically? Provide example for better
> understanding. 

It means "when I scheduled this item, I expected the UTC offset at the
time of the timestamp to be -08 and remain so. It was motivated by
America/Vancouver time zone, but if it changes in future, I do not care
- the scheduled time should remain at specific time point relative to
UTC".

> - The UTC offset is not certain to remain fixed in the future. 

Yes. But fixing UTC offset means that time point is fixed. Example: you
need a timestamp exactly N hours from now. It must not be affected by
time zone rule changes.

> - If you do not have the time of creation of the timestamp above, you
>   cannot know with certainty what was the offset in past, to calculate
>   new UTC offset in case it changed

America/Vancouver in the above timestamp is nothing but a reference
comment. One may or may not use it.

> - As not even time zone is certain to remain in existence in future,
>   you will need to use time zone, in order to derive that future UTC
>   offset correctly. As it could change in mean time.

If timestamp must follow the future time zone rules, can just use 
 [2024-02-04 12:00 @America/Vancouver]

>> [2024-02-04 12:00 @America/Vancouver] will use @America/Vancouver time
>> zone, as it is be defined in you OS time zone database.
>
> If you do not keep UTC offset, you will miss changes in future and
> generate errors.

Only if you care. Maybe it is not an error to follow the future changes.
If you want to be notified, just use [2024-02-04 12:00
@-08,!America/Vancouver] explicitly stating the offset you expect in
future.

>> [2024-02-04 12:00 @-08,!America/Vancouver] (note "!") will use fixed -8
>> offset, but also calculate America/Vancouver time from TZ database,
>> compare it with the time coming from -8 offset, and warn you if there is
>> inconsistency.
>
> The UTC offset is the log what was the UTC offset at the time point
> when timestamp was created, as future UTC offset cannot be known.

Sure. -08 is expected offset.

> Making it "fixed" does not fix it in real time, you are then
> introducing something new than what other programs do with time.

I do not understand this statement.

> I do not think that you need "!", you are creating work not necessary
> for users.

I hope that I clarified the need in the above examples. You may also
refer to the reference in the original proposal. The idea with "!" is
explained in more details.

> If users wish to get some warnings, let them customize single option.

This will be less fine-grained approach. For some timestamps, you don't
need warnings. Of course, default customization may be also provided to
enable warnings for timestamps without "!".

-- 
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>