xref: /aosp_15_r20/system/timezone/RELEASE_NOTES.md (revision 2fd832c65f8b41db7ddb4ac802b9196762fe4888)

### 2022a rev. 2

TZDB 2022b introduces `Europe/Kyiv` and merges more time zones which were
alike since 1970. These changes require ICU patches.

Though the reason why 2022b was released are changes in Chile. As they have
to be delivered by the 3rd of September and ICU patches are not ready,
decision was made to prepare smaller release which does not need ICU patches.

tzdata archieve is prepared manually by applying Iran and Chile changes on
top of 2022a tag.


### 2022a

This update includes pre-1970
[changes](https://github.com/eggert/tz/commit/1edbb16e933a6ba6dceefd2bd7057b5ce00dd13c)
which were reverted manually in Android and resulted in Android releasing
updates we called `2021a rev 2` and `2021a rev 3` instead of tracking TZDB's
`2021b` and `2021c` releases. Android has made changes to reduce the impact of
these changes. This might have app compat issues as some methods in Android's
ICU4J APIs such as `TimeZone.getCanonicalID(id)` will return different time
zone IDs than before. After this release, the canonical zone IDs returned will
be different for some input IDs, and will more often be associated with
different regions.

`Africa/Casablanca` is a time zone modelled by the TZDB using a negative DST
saving to represent the period of Ramadan. Several of Android's embedded time
libraries do not support negative DST savings, so we use TZDB's rearguard
format, which flips standard and daylight saving time definitions for affected
zones. Also, `Africa/Casablanca` transitions follow lunar calendar, which
is not supported by TZif format so transitions are pre-generated (as of now up
to year 2087). As they are pre-generated, the last transition is used for dates
after 2087. Before `2022a`, in rearguard format that last transition was from
standard to daylight saving time. Having DST throughout the year might break
assumptions in software, so as of `2022a` the  last transition is marked as
standard time, even though its offset differs from standard time offset used in
prior transitions.

A standard-to-standard time transition breaks DST saving logic in
Android's `java.util.TimeZone.getDSTSavings()` - it returns 0 instead of 1 hour.
`input_data/iana/tzdb2022a.tar.gz` has [commit](https://github.com/eggert/tz/commit/cec7d9e2e83f8a3faa2367e0d45383a1557889ed)
reverted to bring back the old TZif file. There is no fix yet, it will be like
that indefinitely.

The main reason for the TZDB `2022a` release is a change to the DST transition
for Palestine on 27 Mar 2022. In addition to this year's change, future
predictions have also been [adjusted](https://github.com/eggert/tz/commit/59467e3373a2f90aae3a3c9684ab527855922427)
so the DST transitions for future years are also affected.


### 2021 rev. 3

Like 2021 rev.2 this release is also different from regular updates. It is
closely correlated with IANA's `2021d` and `2021e`. See below for more details.

TZDB version `2021c` reverted most (but not all) time zone merges from `2021b`.
As Android has not applied any of them and there were no other rules update,
it is a no-op for Android.

Then TZDB version `2021d` was released with Fiji changes. That corresponds to
ICU's `2021a2`. But `2021a2` also picked up a
`"Link America/Panama America/Coral_Harbour"` change from IANA's TZDB release
in the backward file.

ICU's `2021a3` is `2021a2` with Palestine changes. No extra change there.

`tzdata2021a.tar.gz` in this Android TZDB update is ICU's [`tzdata2021a3.tar.gz`](https://github.com/unicode-org/icu-data/blob/d90a4eed92e3c5221c4dc1977bfdb7c072a8bb3d/tzdata/tzdata_patch/tzdata2021a3.tar.gz)
with `Link` change mention above reverted. Not reverting it will put
`America/Coral_Harbour` under Panama in `tzlookup.xml`. Right approach here
is to update tooling, but that will take some time.


### 2021a rev. 2

In `2021b` several time zones which were alike since 1970 were merged. It
received backlash in tz mailing-list. Please check
[September archive](https://mm.icann.org/pipermail/tz/2021-September/thread.html)
for discussions around the merges.

This contains a subset of the updates from IANA's 2021b update, but not all
because they cause problems for various libraries and OSes, Android included.
New links cause problems for the tzlookup.xml generation process, which have
yet to be resolved. Android API behavior is influenced by ICU, so while ICU
are forked and until things become clearer, so is Android.

ICU decided to skip zone merge changes and named their release `2021a1`.
Unfortunately there are hardcoded places in Android which expect tzdb version
to be exactly 5 characters and we release it as `2021a rev. 2`.

`input_data/iana/tzdata2021a.tar.gz` is renamed ICU's `2021a1.tar.gz`. As it
is not signed, `tzdata2021a.tar.gz.asc` was deleted for this release only.

`2021a1` contains the following changes applied on top of `2021a`:
```
# Portugal observed DST in 1950
https://github.com/eggert/tz/commit/ed2f9d6b01d1256a4d463d2ceb953e15e1673d72
# Fix Guyana LMT and later historical transitions
https://github.com/eggert/tz/commit/0252f09cdff3769ecbf6adfdaf6c47055bbfb74b
# Add Barbados DST 1942-1944, fix end of LMT
https://github.com/eggert/tz/commit/42efb563b8224a20c1a6480b38427e5b4634da36
# Backzone fixes for Gambia, Malawi, Sierra Leone
https://github.com/eggert/tz/commit/bdb47c5fd68996c04a69d6b23c4c4a5a81df5c95
# Sierra Leone did not use DST 1957-1962
https://github.com/eggert/tz/commit/6982e34ab92cf13f3f3fb20212aca8aa2e4f0aae
# Tonga moved from +12:20 to +13 in 1961, not 1941
https://github.com/eggert/tz/commit/666022ef2a65bb9872ffa6d98cb73236c5f6daa0
# Tonga switched to standard time in 1945, not 1901
https://github.com/eggert/tz/commit/03cc98977ea7c93c49ecb58eae07cd01e9034bfd
# Cook Islands had two Christmases in 1899
https://github.com/eggert/tz/commit/bf12c3ba8513b640b83c245f804c37feeccb862b
# More pre-1978 fixes for Cook and Niue
https://github.com/eggert/tz/commit/a10451bb3fa7f84181f29ac81b06008fd1d81249
# Fix north Vietnam lat+long
https://github.com/eggert/tz/commit/6860c875400b70be52c71d7b7b9642b8667a8112
# Niue left -11:20 in 1964, not 1978
https://github.com/eggert/tz/commit/b73f9fd0364e1795b40cd325661ce609d6126377
# Samoa no longer observes DST
https://github.com/eggert/tz/commit/29583c461a9705118560e02e69bb64a0bf2fce0c
# Jordan now starts DST on February’s last Thursday.
https://github.com/eggert/tz/commit/39df8c8b22605f59f71213cfb92b3fd321e31d3c
```

These changes are in chronological order -- from old to new, so apply them
accordingly.

"Replace Pacific/Enderbury with Pacific/Kanton" change was skipped as it
requires changes in CLDR and `tzdb2021b` was announced late in CLDR's release
cycle.

Code changes were skipped as Android uses fixed version of tzcode, not ToT.