[tz] North Vietnam 1970 to 1975 - Asia/Hanoi belongs into main file

[Alois Treindl]

I want to explain why I find the the comment

# For timestamps in north Vietnam back to 1970 (the tzdb cutoff),
# use Asia/Bangkok;

not sufficient.

I have found that most users of time zone database in Vietnam select the 
Vietnamese city Ho Chi Minh city as their time zone reference.

Nobody in heir right mind will select Asia/Bankok, as this is in 
Thailand and not in Vietnam.

The public geonames.org database  assigns the zone Asia/Ho_Chi_Minh for 
all location in country VN (Vietnam).
This indicates that the comment above is not followed.

The result are incorrect timestamps for half of Vietnam for the years 
1970-1975, ie. after the tzdb cutoff.

These common errors would be avoided if Asia/Hanoi was present in the 
main database.

On 28.06.20 14:06, Alois Treindl wrote:
> (Corrected subject line)
>
> The backzone file contains the zone Asia/Hanoi
>
> It should go into the main file for Asia.
>
> There exists no doubt that in all of what was North Vietnam between at least 1970 and 1975 the timezone was 7h east, and not 8h east as in South Vietnam.
>
> There may be unclear borders, but most of North Vietnam, including its capital, was not unclear at all.
>
> I find it a discrimination of former North Vietnam to not have it represented correctly, at least for the post-1970 period.
>
> What Paul Eggert writes in the comments is a poor excuse.
>  From Paul Eggert (2019-02-19):
> #
> # The Ho Chi Minh entry suffices for most purposes as it agrees with all of
> # Vietnam since 1975-06-13.  Presumably clocks often changed in south Vietnam
> # in the early 1970s as locations changed hands during the war; however the
> # details are unknown and would likely be too voluminous for this database.
> #
> # For timestamps in north Vietnam back to 1970 (the tzdb cutoff),
> # use Asia/Bangkok; see the VN entries in the file zone1970.tab.
> # For timestamps before 1970, see Asia/Hanoi in the file 'backzone'.
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