Time-zone database issues

[Stephen Colebourne]

The IANA time-zone database [1] provides details of how time-zones
change over time. The latest release - 2018f - cannot be processed
successfully by the current JDK parser [2].  A workaround exists
however unlike previous cases of tzdb incompatibility, this time it
makes sense for the JDK parser and API to be changed.

Problem
-----------
The JDK parser and API make the assumption that a time-zone change can
occur at any LocalTime or midnight-end-of-day, ie. from 00:00 to
24:00. Unfortunately, the tzdb source files allow (and now include)
rules outside those valid values, in this case a value of 25:00.
Specifically, the rule that causes problems says that clocks change at
25:00 on the first Saturday on or after the 8th of September.

In the current problematic case, the rule can be rewritten to say that
clocks change at 01:00 on the first Sunday on or after the 9th of
September. However, there are cases where it is difficult to
impossible to rewrite the rule (such as 25:00 on the last Saturday in
a month, difficult because it goes into the next month).

Proposed solution
------------------------

Fixing the parser to handle values like 25:00 would be relatively
easy. However, these rules are also exposed in the public API of
java.time.zone.ZoneOffsetTransitionRule [3]. Currently this class has
methods `getLocalTime()` and `isMidnightEndOfDay()`. These would need
to be deprecated and replaced by a new method `getLocalTimeDuration()`
(or some other name) that returns an instance of `Duration`.

A user of ThreeTen-Backport [4] has provided a branch to do this, so I
know the change to be possible. However, since I have looked at the
code I cannot implement the change in OpenJDK (compromised IP). It
needs a cleanroom implementation by someone else.

Is there agreement on the need for change? Is anyone (Oracle or
otherwise) willing to volunteer do the work?

thanks
Stephen


[1] https://www.iana.org/time-zones
[2] https://bugs.openjdk.java.net/browse/JDK-8212684
[3] https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/time/zone/ZoneOffsetTransitionRule.html
[4] https://www.threeten.org/threetenbp/