RELEASE_NOTES.md - platform/system/timezone - Git at Google

 ### 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.
	### 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.