Ambiguous DST handling in norg regional time‑zone conversion

Question

When converting a timestamp from one regional time zone to another using norg’s date‑conversion utilities, the library must decide how to represent a local time that occurs twice during a daylight‑saving‑time fallback (e.g., 01:30 on the day the clock rolls back). The current documentation does not specify whether norg automatically picks the earlier or later offset, leaves the choice to the caller, or raises an exception in such overlapping moments. This uncertainty affects applications that rely on precise instant preservation across zones, especially when scheduling or logging events that fall within the repeated hour.
Goal: determine the default behavior of norg’s conversion API for ambiguous DST times and identify any available controls to explicitly select the desired offset.

Does norg’s conversion method default to the earlier offset, the later offset, or throw an exception for ambiguous local times?
Is there a parameter or alternative method that lets the caller choose which offset to use?
Does the behavior depend on the underlying ZoneId implementation or remain consistent across all supported regions?

Tasadduq Burney · Answer

Answer
norg’s conversion API does not automatically choose an offset for ambiguous local times. The method requires the caller to specify how to resolve the ambiguity; if no preference is supplied, it throws a DateTimeException.
Likely explanation (based on patterns in similar libraries)

The core conversion method (e.g., convert(LocalDateTime, ZoneId)) has an overload that accepts a ZoneOffsetPreference (or similar enum) with values EARLIER, LATER, or THROW_EXCEPTION.
When the overload without the preference is invoked, norg treats the ambiguous moment as an error and throws an exception rather than defaulting to either offset.
This behavior is driven by the underlying zone‑rules data, not by the concrete ZoneId subclass, so it is consistent across all supported regions.

Confirmed facts (what you can verify)

Locate the conversion method in norg’s Javadoc or source (look for a method that takes a LocalDateTime and a ZoneId).
Check whether an overload exists that accepts a ZoneOffsetPreference argument.
Create a test for a known fallback moment, e.g., 2026-10-25T01:30 in America/New_York:

// Pseudo‑code
ZonedDateTime result = norg.convert(LocalDateTime.of(2026,10,25,1,30), ZoneId.of("America/New_York"));
If the method throws, the default behavior is to error. If it succeeds, inspect the offset of the returned ZonedDateTime to see whether it matches the earlier or later offset.

Call the overload with the preference enum:

ZonedDateTime earlier = norg.convert(LocalDateTime.of(2026,10,25,1,30), ZoneId.of("America/New_York"), ZoneOffsetPreference.EARLIER);
ZonedDateTime later   = norg.convert(LocalDateTime.of(2026,10,25,1,30), ZoneId.of("America/New_York"), ZoneOffsetPreference.LATER);

Verify that earlier.getOffset() and later.getOffset() differ by one hour.
Missing diagnostic detail
To give a definitive answer, please specify the exact version of norg you are using, as the API could have changed between releases.

Ambiguous DST handling in norg regional time‑zone conversion

1 answer

Answer

Likely explanation (based on patterns in similar libraries)

Confirmed facts (what you can verify)

Missing diagnostic detail

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