[tz] Adding a "test" region?

Philip Paeps philip at trouble.is
Wed Jan 24 22:22:19 UTC 2018

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 assumptions.
>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.



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.


Philip Paeps
Senior Reality Engineer
Ministry of Information

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