[tz] Undoing the effect of the new alike-since-1970 patch

Stephen Colebourne scolebourne at joda.org
Tue Jun 8 17:44:00 UTC 2021

On Tue, 8 Jun 2021 at 17:23, Paul Eggert via tz <tz at iana.org> wrote:
> On 6/8/21 1:56 AM, Stephen Colebourne via tz wrote:
> > It is possible to automatically derive the data for group 1 from the
> > data for group 2. The other way around is not possible.
> That's OK, as I'm not proposing the other way around. I'm merely
> proposing a flag to generate either group-1-style or group-2-style data
> from what we have now. This should be doable relatively easily. (And if
> I'm wrong, we can revisit this technical issue of course.)

Are you proposing a makefile option to recreate the original source
files using the data in backzone? That seems much harder work than
doing it the other way around and prone to error. (Remember that
downstream projects need the correct source files, not any other
output file)

One key advantage of the `idmerge` file is that it makes the merge
process obvious. ie. that TZDB favours Berlin over Stockholm/Oslo. I'm
proposing that the historic data is present in its original location
(africa to southamerica). And I propose that the flag and `idmerge`
provide the necessary tools to reduce the file size for those that
need it.

The importance of the full dataset being the default can be seen here
for example:
As can be seen, the docs expect users to download the latest tarball.
It isn't reasonable for TZDB to demand all downstream users change
their URL. Another variant of the same tool:

Here is another example, where a downstream system has had to adapt to
retain compatibility:

I know CLDR has previously expressed significant concern about the
compatibility issue too.


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