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Temporal: Add test coverage for close-together time zone transitions (#4471)

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Check that implementations correctly detect time zone transitions that
are close together. Additionally, test startOfDay() since the time zone
transitions in Brazil occur at midnight.

See https://github.com/tc39/proposal-temporal/issues/3110
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46
test/intl402/Temporal/ZonedDateTime/prototype/getTimeZoneTransition/transitions-close-together.js vendored Normal file
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// Copyright (C) 2025 Igalia, S.L. All rights reserved.
// This code is governed by the BSD license found in the LICENSE file.
/*---
esid: sec-temporal.zoneddatetime.prototype.gettimezonetransition
description: Test TZDB edge case where transitions occur close together
features: [Temporal]
---*/
// This is a list of time zones that have transitions occurring less than two
// weeks apart. (Some additional ones occur in questionable future calculations
// which are not included here.)
// Implementations using a bisect strategy to find the transition times, must
// use a small enough window to catch these transitions.
const testData = {
"Africa/Tunis": [-842918400n /* 1943-04-17T01+01:00 */, -842223600n /* 1943-04-25T03+02:00 */],
"America/Argentina/Tucuman": [1086058800n /* 2004-05-31T23-04:00 */, 1087099200n /* 2004-06-13T01-03:00 */],
"America/Boa_Vista": [970977600n /* 2000-10-08T01-03:00 */, 971578800n /* 2000-10-14T23-04:00 */],
"America/Fortaleza": [970974000n /* 2000-10-08T01-02:00 */, 972180000n /* 2000-10-21T23-03:00 */],
"America/Maceio": [970974000n /* 2000-10-08T01-02:00 */, 972180000n /* 2000-10-21T23-03:00 */],
"America/Noronha": [970970400n /* 2000-10-08T01-01:00 */, 971571600n /* 2000-10-14T23-02:00 */],
"America/Recife": [970974000n /* 2000-10-08T01-02:00 */, 971575200n /* 2000-10-14T23-03:00 */],
"Europe/Riga": [-796777200n /* 1944-10-02T02+01:00 */, -795834000n /* 1944-10-13T02+03:00 */],
"Europe/Simferopol": [-812502000n /* 1944-04-03T03+02:00 */, -811648800n /* 1944-04-13T01+03:00 */],
"Europe/Tirane": [-844556400n /* 1943-03-29T03+02:00 */, -843519600n /* 1943-04-10T02+01:00 */],
"Europe/Vienna": [-781052400n /* 1945-04-02T03+02:00 */, -780188400n /* 1945-04-12T02+01:00 */],
}
for (const [zone, [first, second]] of Object.entries(testData)) {
for (const [label, epochSeconds] of Object.entries({ first, second }) ) {
const transition = new Temporal.ZonedDateTime(epochSeconds * 1_000_000_000n, zone);
const before = new Temporal.ZonedDateTime((epochSeconds - 1800n) * 1_000_000_000n, zone);
const after = new Temporal.ZonedDateTime((epochSeconds + 1800n) * 1_000_000_000n, zone);
assert.sameValue(
before.getTimeZoneTransition("next").epochNanoseconds,
transition.epochNanoseconds,
`${zone} offset transitions close together, next to ${label} transition`
);
assert.sameValue(
after.getTimeZoneTransition("previous").epochNanoseconds,
transition.epochNanoseconds,
`${zone} offset transitions close together, previous to ${label} transition`
);
}
}

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test/intl402/Temporal/ZonedDateTime/prototype/startOfDay/transitions-close-together.js vendored Normal file
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// Copyright (C) 2025 Igalia, S.L. All rights reserved.
// This code is governed by the BSD license found in the LICENSE file.
/*---
esid: sec-temporal.zoneddatetime.prototype.startofday
description: Test TZDB edge case where transitions occur close together
features: [Temporal]
---*/
// Zone America/Noronha (Fernando de Noronha) switched to DST -01:00 according
// to the Brazilian DST rules then in effect on 2000-10-08T00. Then the
// following week on 2000-10-15T00 discarded DST, going back to a permanent
// -02:00 offset. Implementations using a bisect method to find the transition
// times, must use a small enough window to catch these transitions 1 week
// apart.
const noronha = new Temporal.ZonedDateTime(970970400000000000n /* 2000-10-08T01-01:00 */, "America/Noronha");
assert.sameValue(
noronha.startOfDay().epochNanoseconds,
noronha.epochNanoseconds,
"America/Noronha offset transitions close together"
);
// Same deal for zone America/Boa_Vista, but with -03:00 and -04:00
// respectively. Test again with an instance that is not already the start of
// the day.
const boaVistaStart = new Temporal.ZonedDateTime(970977600000000000n /* 2000-10-08T01-03:00 */, "America/Boa_Vista");
const boaVista = new Temporal.ZonedDateTime(970984800000000000n /* 2000-10-08T03-03:00 */, "America/Boa_Vista");
assert.sameValue(
boaVista.startOfDay().epochNanoseconds,
boaVistaStart.epochNanoseconds,
"America/Boa_Vista offset transitions close together"
);
// The same thing occurs in several other Brazilian time zones on the same or
// nearby dates, but these two are sufficient for the test. Other occur at other
// times of the day (see ../getTimeZoneTransition/transitions-close-together.js)
// but those are not relevant for startOfDay().