Re: [PATCH] strbuf: let strbuf_addftime handle %z and %Z itself

> On Mon, Jun 12, 2017 at 5:12 PM, Junio C Hamano <gitster@pobox.com> wrote:
>> René Scharfe <l.s.r@web.de> writes:
>>
>>> Am 07.06.2017 um 10:17 schrieb Jeff King:
>>>> On Sat, Jun 03, 2017 at 12:40:34PM +0200, René Scharfe wrote:
>>>>> Duplicates strbuf_expand to a certain extent, but not too badly, I
>>>>> think.  Leaves the door open for letting strftime handle the local
>>>>> case.
>>>>
>>>> I guess you'd plan to do that like this in the caller:
>>>>
>>>>     if (date->local)
>>>>       tz_name = NULL;
>>>>     else
>>>>       tz_name = "";
>>>>
>>>> and then your strftime() doesn't do any %z expansion when tz_name is
>>>> NULL.
>>>
>>> Yes, or you could look up a time zone name somewhere else -- except we
>>> don't have a way to do that, at least for now.
>>
>> Is that only "for now"?  I have a feeling that it is fundamentally
>> impossible with the data we record.  When GMTOFF 9:00 is the only
>> thing we have for a timestamp, can we tell if we should label it as
>> JST (aka Asia/Tokyo) or KST (aka Asia/Seoul)?

> It's obviously not perfect for all the reasons mentioned in this
> thread, but we already have a timezone->offset mapping in the
> timezone_names variable in date.c, a good enough solution might be to
> simply reverse that lookup when formatting %Z
> 
> Of course we can never know if you were in Tokyo or Seul from the info
> in the commit object, but we don't need to, it's enough that we just
> emit JST for +0900 and anyone reading the output has at least some
> idea what +0900 maps to.

> We could also simply replace "%Z" with the empty string, as the the
> POSIX strftime() documentation allows for:
> http://pubs.opengroup.org/onlinepubs/009695399/functions/strftime.html
> ("Replaced by the timezone name or abbreviation, or by no bytes if no
> timezone information exists.").