2042239 - Implement needs-consensus PR from May 2026 affecting Temporal.Duration rounding

Status: RESOLVED FIXED

(Core :: JavaScript Engine, task, P1)

Description

[Philip Chimento [:ptomato]]

Upstream issue: https://github.com/tc39/proposal-temporal/issues/3316
Test262: https://github.com/tc39/test262/pull/5054

Spec fix reached consensus at May 2026 TC39 meeting.

Comment 1

[Philip Chimento [:ptomato]]

Attachment: Bug 2042239 - Fix faulty shortcut condition in ComputeNudgeWindow. r?anba

There is a condition triggering the special case for avoiding a
disambiguation when calculating the startEpochNs of the bounding window.
This condition is not correct when largestUnit ≠ smallestUnit, and the
smallest unit is 0 while a larger unit is nonzero. The condition only
checks that the smallest unit (r1) is 0, while it should check that all
larger units are 0 as well.

This fix corresponds to a needs-consensus PR that reached TC39 consensus
in the meeting of 2026-05-19.

Upstream links: https://github.com/tc39/proposal-temporal/issues/3316,
https://github.com/tc39/proposal-temporal/pull/3319,
https://github.com/tc39/test262/pull/5054

Tests will be pulled in along with the next test262 update.

Comment 2

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/9bb25c4ee3f0
https://hg.mozilla.org/integration/autoland/rev/553ba7a4620d
Fix faulty shortcut condition in ComputeNudgeWindow. r=anba

Comment 3

[rperta]

https://hg.mozilla.org/mozilla-central/rev/553ba7a4620d