[Bug 269342] historical tzdata lost for many zones following 2021/2022 IANA tz changes

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=269342

            Bug ID: 269342
           Summary: historical tzdata lost for many zones following
                    2021/2022 IANA tz changes
           Product: Base System
           Version: CURRENT
          Hardware: Any
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: bin
          Assignee: bugs@FreeBSD.org
          Reporter: fbsd@opal.com

During 2021 and 2022, the IANA timezone data [IANA-TZ] was changed to link many
zones together if their timezone rules have been the same since the 1970 UNIX
Epoch.

This has led to two undesirable consequences:

1. For many countries/regions, the timezone data is now taken from another
country's/region's definition, resulting in their timezone name confusingly
being reflected as that of the other country/region.

   For example, the following are now all linked to Europe/Berlin:
        Arctic/Longyearbyen
        Europe/Copenhagen
        Europe/Oslo
        Europe/Stockholm
        Atlantic/Jan_Mayen

   Functions that look up the local timezone name now report "Europe/Berlin"
for users in any of these linked countries/regions.

   There are now many such linked regions. Another example: Icelandic users now
see their zone name as "Africa/Abidjan" instead of the expected
"Atlantic/Reykjavik".

   The standard/daylight rules are consistent for these since 1970, so users do
see the correct time, even though the zone name is not as expected.

2.  For applications that use dates PRIOR to the 1970 Epoch, historical
standard/daylight rule information for each country/region is now lost, it now
being taken from the common zone's definition. Even though the linked zones'
rules have been consistent since 1970, their rules are very likely to have been
different PRIOR to 1970. While that data still exists in the tzdata database,
it is no longer installed and so no longer accessible to applications.
Applications presenting historical dates/times may therefore reflect incorrect
timezones for linked regions.

There has been debate on the IANA timezone lists as to whether these linked
zones were a good idea.

There appear to have been two solutions to allow systems to revert to
installing the historical data for each region:

A. The forked global-tz database [GLOBAL-TZ] which mirrors the IANA data but
which installs zones without links and keeps each zone's historical data.

B. New settings in the IANA tzdata Makefile, PACKRATDATA and PACKRATLIST,
which, the comment says, cause the data to be installed the same way as
global-tz does.  It is necessary to set:
        PACKRATDATA=    backzone
        PACKRATLIST=    zone.tab

I would like to propose that FreeBSD reverts to installing historical data for
each country/region so that both issues 1. and 2. above are corrected.  The
simplest solution would appear to be to set the two PACKRAT variables in
src/contrib/tzdata/Makefile as shown in B.


[IANA-TZ]   https://github.com/eggert/tz
[GLOBAL-TZ] https://github.com/JodaOrg/global-tz

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