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LibJS: Handle time zone gaps in JS::utc_time

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Commit 88365031f2 added support for time
zone gaps in general, but missed this method.
This commit is contained in:
Timothy Flynn 2026-03-20 07:59:15 -04:00 committed by Jelle Raaijmakers
parent d139b519d3
commit b3795eb5bb
2 changed files with 35 additions and 8 deletions
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29
Libraries/LibJS/Runtime/Date.cpp
View file

@ -1,6 +1,6 @@
/*
* Copyright (c) 2020-2023, Linus Groh <linusg@serenityos.org>
* Copyright (c) 2022-2024, Tim Flynn <trflynn89@ladybird.org>
* Copyright (c) 2022-2026, Tim Flynn <trflynn89@ladybird.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
@ -529,7 +529,11 @@ double utc_time(double time)
// b. Let possibleInstants be GetNamedTimeZoneEpochNanoseconds(systemTimeZoneIdentifier, isoDateTime).
auto possible_instants = get_named_time_zone_epoch_nanoseconds(system_time_zone_identifier, iso_date_time);
// c. NOTE: The following steps ensure that when t represents local time repeating multiple times at a negative time zone transition (e.g. when the daylight saving time ends or the time zone offset is decreased due to a time zone rule change) or skipped local time at a positive time zone transition (e.g. when the daylight saving time starts or the time zone offset is increased due to a time zone rule change), t is interpreted using the time zone offset before the transition.
// c. NOTE: The following steps ensure that when t represents local time repeating multiple times at a negative
// time zone transition (e.g. when the daylight saving time ends or the time zone offset is decreased due to
// a time zone rule change) or skipped local time at a positive time zone transition (e.g. when the daylight
// saving time starts or the time zone offset is increased due to a time zone rule change), t is interpreted
// using the time zone offset before the transition.
Crypto::SignedBigInteger disambiguated_instant;
// d. If possibleInstants is not empty, then
@ -539,13 +543,22 @@ double utc_time(double time)
}
// e. Else,
else {
// i. NOTE: t represents a local time skipped at a positive time zone transition (e.g. due to daylight saving time starting or a time zone rule change increasing the UTC offset).
// ii. Let possibleInstantsBefore be GetNamedTimeZoneEpochNanoseconds(systemTimeZoneIdentifier, TimeValueToISODateTimeRecord(tBefore)), where tBefore is the largest integral Number < t for which possibleInstantsBefore is not empty (i.e., tBefore represents the last local time before the transition).
// iii. Let disambiguatedInstant be the last element of possibleInstantsBefore.
// i. NOTE: t represents a local time skipped at a positive time zone transition (e.g. due to daylight
// saving time starting or a time zone rule change increasing the UTC offset).
// FIXME: This branch currently cannot be reached with our implementation, because LibUnicode does not handle skipped time points.
// When GetNamedTimeZoneEpochNanoseconds is updated to use a LibUnicode API which does handle them, implement these steps.
VERIFY_NOT_REACHED();
// ii. Let possibleInstantsBefore be GetNamedTimeZoneEpochNanoseconds(systemTimeZoneIdentifier, TimeValueToISODateTimeRecord(tBefore)),
// where tBefore is the largest integral Number < t for which possibleInstantsBefore is not empty (i.e.,
// tBefore represents the last local time before the transition).
// NB: We implement this by finding the next UTC offset transition after one day before the skipped time,
// which is guaranteed to be before the gap. The last valid instant before the transition is one
// nanosecond before the transition instant.
auto epoch_nanoseconds = get_utc_epoch_nanoseconds(iso_date_time);
auto day_before = epoch_nanoseconds.minus(Temporal::NANOSECONDS_PER_DAY);
auto transition = Temporal::get_named_time_zone_next_transition(system_time_zone_identifier, day_before);
VERIFY(transition.has_value());
// iii. Let disambiguatedInstant be the last element of possibleInstantsBefore.
disambiguated_instant = transition->minus(1_bigint);
}
// f. Let offsetNs be GetNamedTimeZoneOffsetNanoseconds(systemTimeZoneIdentifier, disambiguatedInstant).

14
Tests/LibJS/Runtime/builtins/Date/Date.js
View file

@ -85,3 +85,17 @@ test("tuple constructor overflow", () => {
expect(date.getMilliseconds()).toBe(655);
expect(date.getDay()).toBe(4);
});
test("time zone gap", () => {
const originalTimeZone = setTimeZone("Europe/London");
const date = new Date(2026, 2, 29, 1, 30, 0);
expect(date.getFullYear()).toBe(2026);
expect(date.getMonth()).toBe(2);
expect(date.getDate()).toBe(29);
expect(date.getHours()).toBe(2); // Jumps one hour ahead.
expect(date.getMinutes()).toBe(30);
expect(date.getSeconds()).toBe(0);
setTimeZone(originalTimeZone);
});