[tz] Add new timezone for Hanoi Capital, Vietnam

[Tim Parenti]

On Mon, 18 Feb 2019 at 12:23, Guy Harris <guy at alum.mit.edu> wrote:

> If so, then is the reason that we have
>
>         Link Asia/Bangkok Asia/Phnom_Penh       # Cambodia
>         Link Asia/Bangkok Asia/Vientiane        # Laos
>
> but don't have, for example,
>
>         Link Asia/Bangkok Asia/Hanoi            # (North) Vietnam
>
> that Asia/Phnom_Penh and Asia/Vientiane existed as separate entries before
> being combined with Asia/Bangkok, so that we need to keep their entire
> around for backwards compatibility, but there had never been an Asia/Hanoi?


It looks like that's indeed what happened.  Thanks for jogging my memory.
So I guess it wasn't an omission so much as an awkward and
poorly-documented decision:

   - Asia/Phnom_Penh and Asia/Vientiane (which had existed prior) were
   combined with Asia/Bangkok on 2014-10-04 in
   https://github.com/eggert/tz/commit/6f7ddecfb036e13a1132181cfaa8ab3e070fc9e8
   - Asia/Hanoi (which had NOT existed prior) was added to backzone on
   2014-10-11 in
   https://github.com/eggert/tz/commit/bcb616ca405583de10e6e8c85951720ef066877a

If we had known about the differences in Asia/Hanoi at least one release
prior to this merging (and I recall all of this came up as part of the same
discussion), then Asia/Hanoi would have needed to become a separate zone at
that time.  But because we first took the opportunity to coalesce the other
zones, Asia/Hanoi's history could be coalesced as well, which is why it
landed only in 'backzone' and not in 'asia'.

I do think this boils down to a judgement call, though.  There certainly
could be an appearance of bias (though none was intended, it simply wasn't
necessary to include Asia/Hanoi for backwards compatibility as it hadn't
yet existed).  Given that and the other complexities here, I would
personally be inclined to move the Asia/Hanoi into the mainstream
distribution, but I can absolutely see how others involved in the
maintenance here may disagree.  At the very least, better documentation in
the 'asia' file is a pretty clear must.

--
Tim Parenti
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