[tz] Removing systemv, pacificnew, Rule TYPEs, zic -y

Paul Eggert eggert at cs.ucla.edu
Sun Oct 4 21:12:31 UTC 2020

On 10/4/20 12:30 PM, Michael H Deckers via tz wrote:
>     SystemV clocks have been "computer-based clocks that
>     track civil time", and they are no longer "recorded".

There is a bit of a second-order effect here, since SystemV clocks were never 
intended to track civil time for the long haul; they were intended only to track 
it during a single period when the authorities did not change the rules, and 
when rules used the Gregorian calendar in one of a few stereotyped ways. You're 
right that in some sense a SystemV data entry establishes a new kind of "civil 
time", but that's only in the sense that tzdb's Europe/Amsterdam establishes a 
new kind of "civil time" that differs in minor ways from civil time actually 
observed in Amsterdam long ago (due to deficiencies in tzdb).

>     Actually, with very few exceptions, tzdb currently records the
>     current state, the predicted future, and a selected part of the
>     history, of civil time scales (not of computer clocks) 

That's a better way to put it, yes. I installed the attached proposed patch to 
do something briefly along those lines. There's no need for more discussion at 
that point since this is an intro sentence and the details are explained later 

>     The dst bit is a special attribute for POSIX, while other
>     attributes required by other computer systems (eg, the
>     offset to standard time and the summer time indicator) are
>     currently not supported by tzdb.

I wouldn't go that far; .zi files contain info supporting offset to standard 
time and a "summer time indicator" (though I don't know how exactly that would 
differ from POSIX's tm_isdst).

To some extent this part of tzdb is arbitrary anyway, as it's not entirely clear 
what is meant by that stuff and hardly anybody cares about it anyway. Right now, 
tzdb surely disagrees with Yukon law in this area but Yukon's clocks are right 
and nobody has complained here.
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