[tz] What data should TZDB offer?

[Clive D.W. Feather]

Derick Rethans via tz said:
> > 2) Negative DST
> > Negative DST in the source files continues to be a problem, but we
> > should address other issues first.
> 
> When I first highlighted this Irish case 
> (https://mm.icann.org/pipermail/tz/2017-December/025621.html), it was 
> never my intention that the tz data was changed to negative DST - I was 
> originally only pointing out that IST isn't only Iran Standard Time, but 
> also Irish Standard Time. I don't mind how it is recorded, as long as it 
> produces the right output (in the form of transitions).

If negative DST represents what actually happens in the real world, then
that's what we should be using.

If implementations can't cope with negative DST, then they have bugs in
them and/or don't match the real world. They need to change; we should not
be lying to everyone just because some people won't face reality.

(I don't object to a mechanism for people to do a build with the lies in,
provided they have to explicitly accept it. Lies shouldn't be the default.)

The other thing I think we need to discuss in this debate is the intent of
pre-1970 data. It should be clear to people what this data is meant to
cover.

I was under the impression that pre-1970 data represents the time in at
least some part of the zone. So, at present, the Berlin zone has pre-1970
data that represents at least part of Germany and the Stockholm zone has
pre-1970 data that represents at least part of Sweden.

If these are merged, the resulting zone has two names but both only contain
pre-1970 data for part of Germany. In this case, it needs to be made very
clear that the area covered by Stockholm is "Germany and Sweden", not
"Sweden". The problem appears, to me, to be two zones that have the same
contents but different descriptions. That would need to be fixed.

(Personally, I'd like all the pre-1970 data that we used to have to still
be available. But I understand that Paul doesn't want to have to change
dozens of zones that last differed in the 19th century just because of a
change in the 21st. There ought to be a solution to this.)

-- 
Clive D.W. Feather          | If you lie to the compiler,
Email: clive at davros.org     | it will get its revenge.
Web: http://www.davros.org  |   - Henry Spencer
Mobile: +44 7973 377646