[tz] Add new timezone for Hanoi Capital, Vietnam

[Tim Parenti]

On Mon, 18 Feb 2019 at 03:53, Guy Harris <guy at alum.mit.edu> wrote:

> If *post*-unification time - which is post-1970 - doesn't match
> Asia/Bangkok, then Asia/Bangkok should not be used for any part of Vietnam;
> there should be one or more Asia/{whatever} for Vietnam from 1970 to the
> present.


To be a bit more precise, for our purposes, I mean when the *clocks* were
reunified, independent from the various stages of political reunification.
Our data has that occurring on 1975-06-13.  Since that time, all of Vietnam
has agreed with Asia/Bangkok, so there is no issue there.


> If Vietnam's pre-unification offset or rules were different between the
> north and the south from 1970 to 1976, then "one or more" means "at least
> two", e.g. Asia/Hanoi and Asia/Ho_Chi_Minh (even if it was called Saigon in
> 1970).


This, however, is where the need for a second zone for Vietnam arises.  And
indeed there are already two listed in zone1970.tab (Asia/Ho_Chi_Minh and
Asia/Bangkok); it's just that one of them happens to be modeled by a city
outside Vietnam.  That is not considered a problem per theory.html.

--
Tim Parenti
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