[BUG] Shifting timestamp hours around daylight transition (was: Clock dates - org-shiftdown not working)

[Ihor Radchenko <yantar92@posteo.net>]

Tebe Nigrelli <nigrellitebe@gmail.com> writes:

> On a clean configuration, applying org-shiftdown does not work for the
> following date format, written as a clock. I want to reduce the number of
> hours
> on the second date from "03:" to "02:". This is what happens if I apply
> org-shiftdown:
>
> Instructions to reproduce the bug:
> Try doing org-shiftdown on the minutes "05" or the hours "03".
> Result:
> CLOCK: [2023-03-25 Sat 21:40]--[2023-03-26 Sun 03:05] =>  4:25

At least in some parts of Europe, the time from 2023-03-26 2:00 to
2023:03-26 2:59 does not exist. It is the hour-forward daylight
transition.

So, when Org is trying to change the data to 2023-03-26 2:05, Emacs date
library refuses and instead sets the closes valid time.

I am not sure would be the best course of action here.
1. We can jump over the invalid hours in the direction requested by user
2. We can throw an error, making the user aware about the daylight
   thing.

I am more in favour of (2) because things like this are easy to overlook.

-- 
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>