Local day bounds had three implementations. The day-key one read the zone
offset at UTC midnight, which on a transition day in zones far from UTC
(Pacific/Auckland, Australia/Sydney) is the offset after the change, so the
day started an hour off. The instant one converged on local 00:00, which in
zones that skip midnight (America/Santiago, America/Havana) does not exist,
and returned 23:00 of the previous day.
startOfLocalDayKey and localDayWindow in lib/tz/local-day are now the only
implementation: the first instant that reads the day, tried under every
offset in force around it. A skipped wall clock resolves to the moment the
clocks jump, the day-keyed copies in the measurement drains, the compliance
rollups and the dashboard batch window are gone, and the noon and mid-hour
anchors use the same converge.
Marc-André Bombeck
73e0653b2c