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

[Paul Eggert]

On 2/20/19 9:21 AM, Hans-Joerg Happel wrote:
> Is anybody aware of how upstream software based on tzdb is typically 
> dealing with "Links"? It seems, Java does list time zone ids stemming 
> from "links", while "tzselect" on my Ubuntu machine does not seem to 
> use them - at least not in the interactive configuration [1]

Ubuntu is probably using tzselect from a recent tzdb distribution. 
tzselect takes its list of names from zone1970.tab, whose names 
currently consists of the Zone names in the following files:

africa antarctica asia australasia europe northamerica southamerica

except for the following Zone names, which are present in the above 
files only for backwards compatibility with long-obsolete Unix systems:

CET CST6CDT EET EST EST5EDT HST MET MST MST7MDT PST8PDT WET

zone1970.tab does not list Link names, as there's no technical need to 
use a Link name except for backward-compatibility reasons.

It might make sense at some point to move the CET etc. entries and the 
Link lines to some other file to make it easier for distributions to 
exclude these entries if they don't have backward-compatibility issues.