[tz] zic changes (2/2)

[Guy Harris]

On Mar 3, 2016, at 8:37 AM, Paul Eggert <eggert at cs.ucla.edu> wrote:

> On 03/02/2016 09:38 PM, Random832 wrote:
>> Are you
>> saying that the_actual intent_  of the POSIX committee was to forbid the
>> use of the traditional System III timezone format, rather than allowing
>> it (as the brackets imply) and having the rules be
>> implementation-defined?
> 
> That's what I was saying, yes, but it appears I was incorrect. The original intent was to allow the syntax TZ='PST8PDT', but to leave the daylight-saving rules unspecified in this case. Hence the test case that prompted this thread (though most likely illustrating a bug in glibc) does not illustrate a violation of POSIX, because portable programs should not assume that TZ strings like 'PST8PDT' have any particular behavior with respect to when DST starts and stops.

And neither should users, unless they happen to know how the platforms they're using work.

> This is all stated clearly in the rationale for POSIX 1003.1-1988. I guess that part of the rationale has been discareded in more recent editions of the standard, which makes the current standard confusing (it confused *me*, anyway).

I think I'll file a defect report on that; it either needs to explicitly say, in the standard itself, that the behavior, if you omit the DST start and end information, is undefined or implementation-defined (I leave it up to them to choose), or explicitly require a particular behavior.

> To try to save Guy Harris some time in reply, I should mention that there is an attribution error in rationale quoted above.

Thanks.  Dunno why they ignored, for example, Chris Torek, Mary (Mark) Horton, Robert Elz, Dennis Mumaugh, Bob Devine, Bob Toxen, or Ron Tolley, to list the folks other than Olson and Harris given as people "currently on the list" in Arthur's "seismo!elsie!tz ; new versions of time zone stuff" message from November 1986.