[tz] Lack of "initial" transitions for some zones

[Howard Hinnant]

On Jul 21, 2015, at 11:09 AM, Howard Hinnant <howard.hinnant at gmail.com> wrote:
> 
> On Jul 21, 2015, at 10:47 AM, Jon Skeet <skeet at pobox.com> wrote:
>> 
>> I suspect this is just a matter of how the data has been specified, but it's a little odd...
>> 
>> I'm looking at the output of zic for each zone, and almost all zones start with a "transition" for some timestamp in the long distant past - including fixed zones such as UTC and Etc/*.
>> 
>> However, the legacy "root" zones of CET, EET, PST8PDT etc don't have this initial "transition" in the file - unless I'm misinterpreting it, which is always a possibility.
>> 
>> Would it make sense to adjust either the data or zic to make all zic output (in the 8-byte-timestamp format, at least) cover all of time? I realize that this "extra" data (presumably an insertion of "standard time until the first transition") may well not be historically accurate - but I doubt that it would be any less accurate than other zones in a similar situation.
> 
> Just zeroing in on PST8PDT, it looks to me like its initial state (from the beginning of time) is unambiguously:
> 
> -08:00:00 standard PST
> 
> I get this by using:
> 
> Zone	PST8PDT		 -8:00	US	P%sT
> 
> And “falling off the beginning” of the US Rule list (by finding the first Rule with 0 save):
> 
> Rule	US	1918	1919	-	Oct	lastSun	2:00	0	S

And subsequently its first transition is determined by this this Rule:

Rule	US	1918	1919	-	Mar	lastSun	2:00	1:00	D

PST8PDT
Initially:           -08:00:00 standard PST
1918-03-31T10:00:00Z -07:00:00 daylight PDT
1918-10-27T09:00:00Z -08:00:00 standard PST
1919-03-30T10:00:00Z -07:00:00 daylight PDT
…

Howard