android13/system/timezone/RELEASE_NOTES.md

2022a

This update includes pre-1970 changes 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 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 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 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 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.