Hello tzdata maintainers,

I would like to propose a feature enhancement for the zic compiler.

Currently, the NOS time zone rules are defined as:

Rule NOS 1970 2037 - Jan 27 23:43:01 2:0 SDST

Rule NOS 1970 2037 - Jan 28 0:51:01 0 S

Zone OS/NOS +7:0:0 NOS NO%s

Issue:

- The first rule enters DST at 23:43:01 with a +2 hour offset, moving local time to 01:43:01.

- The second rule is intended to revert to standard time at 00:51:01.

- Due to the offset, 00:51:01 local time never occurs, so the second rule will never trigger.

- This creates unreachable local times and may cause incorrect results in time calculations.

Proposal:

- Add validation in the zic command to detect DST rules where the offset causes the subsequent rule's local time to be unreachable.

- The validation could issue a warning or error to alert the author of potentially invalid rules.

- This would improve the robustness of time zone definitions and prevent subtle bugs in downstream applications.

Thank you for your consideration.

Best regards