[tz] tzdb timezone names/identifiers and links (was: Add new timezone for Hanoi Capital, Vietnam)

[Guy Harris]

On Feb 19, 2019, at 11:00 AM, Stephen Colebourne <scolebourne at joda.org> wrote:

> On Tue, 19 Feb 2019 at 16:35, Paul Eggert <eggert at cs.ucla.edu> wrote:
> 
>>> setting "Vietnamese" data or systems to an "Asia/Bangkok" tzdb
>>> identifier would, to some degree, effectively tie that data to Thai
>>> legislation.
> 
> Vietnamese systems looking to future dates should be set to
> Asia/Ho_Chi_Minh, shouldn't they?

Currently, they agree, so it doesn't matter whether, for current dates/times, you use Asia/Bangkok or Asia/Ho_Chi_Minh.

In the past, they didn't agree, so, to correctly convert dates/times between 1970 and reunification in 1975, you should use Asia/Bangkok for North Vietnam and Asia/Ho_Chi_Minh for South Vietnam.

If Vietnam changes in such a fashion so that future dates will not properly be handled by Asia/Bangkok, they won't properly be handled by the current Asia/Ho_Chi_Minh.  In that case, we should probably bring Asia/Hanoi into asia from backzone, and update both Asia/Hanoi and Asia/Ho_Chi_Minh to the new rules, so that locations in what was North Vietnam would use Asia/Hanoi and locations in what was South Vietnam would use Asia/Ho_Chi_Minh.