[tz] Adding a "test" region?

Philip Paeps philip at trouble.is
Wed Jan 24 22:30:45 UTC 2018

On 2018-01-24 23:22:19 (+0100), Philip Paeps wrote:
>On 2018-01-24 16:36:45 (-0500), Paul G wrote:
>>All this hubbub about the negative SAVE values in the tzdb source 
>>code makes it pretty obvious that downstream consumers are making 
>>some assumptions about undocumented features of the tzdb code. I'm 
>>wondering if it might be worth it to add a new region that contains 
>>fictional time zones that have properties that are perfectly valid 
>>but are edge cases that might be improperly handled downstream. It's 
>>probably a good idea to have this sort of thing in place *before* 
>>some region makes a change that actually violates one of these 
>>A few example test cases I can think of (but I assume others will 
>>have *many* other ideas):
>>- Zone with negative DST
>>- Zone with large DST offset and/or large standard offset
>>- Zone with 3, 4 or 5 offsets per year
>>- Zone which goes from STD->DST with no change in offset.
>>- Zone with new rules that don't take place until after 2038
>>- Zone with arbitrary DST offsets (10m15s, for example)
>>- Zone that corresponds to TAI (e.g. offsets change to compensate for leap seconds)
>I think this is an excellent idea.  But it should be a very obviously 
>fictional region -- obvious enough even to end consumers that it can 
>be distributed default enabled and not hidden behind a build-time knob 
>nobody will ever touch.  So it should not look like a test to the 
>casual lazy distributor who doesn't want to distribute test code.
> Dystopia/Isle_of_Negative_Save
> Dystopia/Half_Hour_Bay
> Dystopia/Fifteen_Minutes_Late_Land
> Dystopia/Fifteen_Minutes_Early_Town
> Dystopia/Twice_Yearly_DST_Ville
> Dystopia/...
>It can be Utopia too.  It can be anything other than "Test".  People 
>will just disable "Test" and not distribute it.
>>Downstream consumers could then use this in their test suites and be 
>>effectively "on notice" that they should be able to handle these 
>>sorts of cases, even though we have no examples of them existing in 
>>the wild (though there's actually some case to be made for 
>>interpreting TAI as a time zone, in which case that one *does* exist 
>>in the wild).
>If it's going to be surrounded by "test" fences, nobody is every going 
>to actually test it.  If we make it obviously fictional, it can be on 
>by default an distributed with the rest of the data.

Come to think of it - it may be wiser to make it a subregion rather than 
a new region.  Possibly under Arctic since there's only one zone there 
with a population of well under 10,000 humans.


Rationale: systems may get confused if the top-level regions increase 
but are likely already more or less accustomed to changes at the second 


Philip Paeps
Senior Reality Engineer
Ministry of Information

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