[tz] RFC 8536bis

[Paul Eggert]

On 1/31/24 11:39, Michael H Deckers wrote:
>> There's no such feature in tzcode. I don't recall such a feature being 
>> discussed - could you point us at any thread in the archive?
> 
> 
> 
>     From NEWS for release 2014b:
> 
>          Changes affecting code
> 
>         'zic' and 'localtime' no longer reject locations needing four 
> transitions
>          per year for the foreseeable future.  (Thanks to Andrew Main 
> (Zefram).)

That merely causes zic to accept .zi input containing four transitions 
per year for the foreseeable future. Input like this, for example:

   Rule Troll 2005 max - Mar       1 1:00u 1:00 +01
   Rule Troll 2005 max - Mar lastSun 1:00u 2:00 +02
   Rule Troll 2005 max - Oct lastSun 1:00u 1:00 +01
   Rule Troll 2004 max - Nov       7 1:00u 0:00 +00
   Zone Antarctica/Troll 0    -     -00 2005 Feb 12
                         0:00 Troll %s

(This isn't in tzdata, but it could be once we can assume tzcode 2014b 
or later.)

When zic sees input like this, it generates a big TZif file with 
explicit transitions out to the year 2407 (2005 + 402 years). The big 
TZif file does not have a TZ string, because no TZ string can represent 
all these transitions.

Previous to 2014b, zic would reject this .zi input; and pre-2014 
localtime would not always work on the big TZif files that 
2014b-or-later zic generates with this .zi input.

Although it might be nice for some future RFC 8536 edition to handle 
Troll, and for tzcode to support it, that's not in the current draft.