[tz] Issues with pre-1970 information in TZDB

[Guy Harris]

On Sep 23, 2021, at 3:20 PM, Tom Lane <tgl at sss.pgh.pa.us> wrote:

> For example, if Norway someday changes its laws such that
> it's no longer identical to Europe/Berlin, then it's a whole lot less
> painful all around if Europe/Oslo already exists and is already being used
> by most of the affected users.  They'll just automatically get the right
> time from a tzdb update, without having to adjust their settings.

It already exists, *and will continue to exist with Paul's most recent changes*.

With those changes, it will be a Link rather than a Zone, but that does not prevent any software from using Europe/Oslo as a tzid.  Systems that use the current location, if available, can continue to choose Europe/Oslo for locations in Norway (tzdb region boundaries aren't maintained by the tzdb project, and they could continue to treat Europe/Oslo as a separate tzdb region).

The issue here is whether any software *above* the tzdb project's reference implementation currently uses backzone tzids, and, if they don't, whether they will stop using Europe/Oslo if it's moved to backzone.