FW: missing extension rules

Olson, Arthur David (NIH/NCI) [E] olsona at dc37a.nci.nih.gov
Thu Sep 29 13:59:34 UTC 2011

I'm forwarding this message from Zefram; since sending it, Zefram has subscribed to the time zone mailing list.


-----Original Message-----
From: Zefram [mailto:zefram at fysh.org] 
Sent: Wednesday, September 28, 2011 6:10
To: tz at lecserver.nci.nih.gov
Subject: missing extension rules

I've found a problem with the tzfiles for Africa/Cairo and
America/Argentina/San_Luis.  They both show a last known transition
in the recent past, and surprisingly lack a POSIX-TZ-format rule for
extending the zone into the future.  My tzfile parser treats a zone
with no extension rule as being undefined for any time following the
last explicit transition, so for these two zones it reckons the zone is
undefined for the present.

In the source files they're each currently configured to observe a set of
DST rules, and the ruleset has no transitions configured for the future.
So for the present and foreseeable future, the zone is on a constant
offset with no DST transitions.  The tzfile reflects that by showing
no transitions from the present up to 2038 (where zic always fills in
a complete set of expected transitions).  It should be trivial to also
reflect that foreseen behaviour in a POSIX-TZ string that just gives a
fixed offset and no DST rule.  For example, Africa/Cairo should clearly
have "EET-2".

I could have a go at a zic patch to fix this, if the regular zic hackers
would like to work that way.

For America/Argentina/San_Luis there's an extra wrinkle: the last known
transition is a transition *to* DST.  Its fixed-offset foreseeable
behaviour therefore has a fixed is_dst=1, which is moderately silly.
It's arguable that in this case it would be incorrect to give a "WARST3"
extension rule, because that doesn't accurately express the DST status.
Since that DST transition was in 2009, it's also a good bet that they
haven't stayed continuously on DST since then, of course.


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