[tz] Change DTS and time zone for Morocco

Paul Eggert eggert at cs.ucla.edu
Tue Nov 12 20:06:53 UTC 2019

On 11/12/19 1:01 AM, liuchao (CR) wrote:
> The Kingdom of Morocco now 
> remains permanently set to UTC+01:00 instead of following an earlier 
> plan to return to UTC+00:00 on October 28, 2018.

Yes, that's right. Standard time in Morocco is now +01.

> But the data in Africa doesn’t change. There still are four clock changes in 2018

On 2018-10-28, Morocco switched its standard time from +00 to +01 
without changing its clocks, instead of its previous practice of 
switching from DST (+01) to standard time (+00) in fall. So from the 
tzdb point of view, the only thing that happened on 2018-10-28 is that 
the tm_isdst flag changed from 1 to 0 at 03:00 local time.

> on May 5 2019, the time jumps from 02:59:59 to 02:00:00, the isdst flag 
> should change from 1 to 0.

That's not how the mainline tzdb models Ramadan in Morocco. tzdb says 
that standard time in Morocco is +01 (as noted above), and that daylight 
saving time is +00 during Ramadan. In other words, daylight saving time 
has a smaller UTC offset than standard time, a situation that is unusual 
but is allowed by POSIX and by tzdb.

Ireland is similar.

> However, I don’t understand why it’s only changed in rearguard format.

Some downstream users don't yet handle this situation, and the rearguard 
format allows them to get their work done in the meantime. But really, 
if you're doing work in this area you should support so-called "negative 
DST", as it is used occasionally and POSIX requires support for it.

More information about the tz mailing list