[tz] zic changes (2/2)

Paul Eggert eggert at cs.ucla.edu
Thu Mar 3 02:08:30 UTC 2016

Brian Inglis wrote:
> On 2016-03-02 16:19, Ian Abbott wrote:
>> On 03/02/16 23:02, Paul Eggert wrote:
>>> The TZ string "PST+8PDT" doesn't conform to POSIX,
>> It doesn't?
> It does appear to conform - see:
> http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap08.html#tag_08_03

It "conforms" in the sense that its syntax matches the POSIX spec. However, no 
semantics are specified by POSIX for what daylight-saving rules are in effect 
when TZ="PST+8PDT" is in the environment.  Glibc is within its rights, for 
example, to assume that DST in effect only one second during the year -- or even 
not in effect any time.

I vaguely recall older versions of POSIX not allowing the syntax "PST+PDT", 
though I could be wrong. I imagine the current POSIX spec is simply a typo, 
since I can't imagine that it's intended for users to employ a syntax whose 
semantics are unspecified.

Also, I think it's a glibc bug, in the sense that I don't think the current 
behavior is intended by the glibc maintainers. Still, portable programs 
shouldn't use TZ="PST+8PDT" or TZ="PST8PDT" or anything like that.

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