[tz] Some thoughts about the way forward

Paul Eggert eggert at cs.ucla.edu
Fri Sep 24 22:22:18 UTC 2021

On 9/24/21 2:10 AM, Jon Skeet wrote:
> I'd need to see exactly what's proposed, as would others, but I'm happy to
> look.

OK, I checked old releases and a common pattern was to replace nine 
Zones with Links (done, for example, in 2014g, 2014h, and 2014j). This 
was the median number of replaced Zones per link, in releases between 
2013 and 2015. So a patch is attached, to do something similar this time 
for 2021b. Although the size of this patch may appear forbidding, it 
greatly shrinks the distance between 2021a and 2021b.

The effect of this patch is to revert all the disputed changes, except 
for the changes to the following nine Zones which are still moved to 
'backzone': Africa/Accra, America/Atikokan, America/Blanc-Sablon, 
America/Creston, America/Curacao, America/Nassau, America/Port_of_Spain, 
Antarctica/DumontDUrville, Antarctica/Syowa.

These Zones were chosen by using the following shell command:

   git diff 2021a..39df8c8b22605f59f71213cfb92b3fd321e31d3c backzone |
   awk '/^+Zone/ && $2 != "Pacific/Kanton" && $2 != "Pacific/Enderbury" 
&& $2 != "Africa/Blantyre" {
     print $2
   }' | head -n 9 | sort

In other words: look at all the Zones moved to backzone since 2021a by 
the current development database, in the order that 'git diff' mentions 
the Zone, and choose the first nine Zones (excluding Pacific/Kanton 
Pacific/Enderbury, which is part of a change not being disagreed about, 
and Africa/Blantyre, which was already in 'backzone').

I view this as an major concession on my part, as it will cause 2021b to 
fix the equity problem only part way, meaning that we'll need about four 
releases to finish the job if we make similarly-sized fixes in the 
future. However, this does address the concern about the number of 
changes by 2021b to pre-1970 timestamps, as we've dealt with changes of 
this size multiple times before. Plus, this approach restores 2021a's 
Europe/Oslo and Europe/Stockholm, the two Zones most-commonly mentioned. 
(I did not tweak the shell script just to save those two Zones for now.) 
The intent is to move forward with this work in later releases.

> we really need a change for Samoa ASAP.

And we now get to throw Jordan into the mix....

I realize that there's not time to do careful review of this patch 
before the Samoa change needs to take effect. However, since this patch 
is simply a reversion, it should be OK. I have applied my usual tests to 
the resulting tzdb and it succeeds. This is pretty much how similar 
patches were tested back in 2014 etc., so this should be good to go.

I realize that there will still be disagreement about the specific 
contents of the release 2021b that results from this patch (along with 
the usual administrivia). We can address that in a followup patch as 
quickly as may be, and continue to work forward to a better approach.
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