1978239 - Temporal's "constrain" behavior in "chinese" and "dangi" calendars is not spec-compliant

Status: UNCONFIRMED

(Core :: JavaScript: Standard Library, defect, P3)

Description

[[:fabon]]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:140.0) Gecko/20100101 Firefox/140.0

Steps to reproduce:

console.log(
  Temporal.PlainDate.from({
    year: 2025,
    monthCode: "M07L",
    day: 1,
    calendar: "chinese",
  }).monthCode, // "M07L" doesn't exist in 2025, should be "M07"
  Temporal.PlainDate.from({
    year: 2025,
    monthCode: "M06L",
    day: 1,
    calendar: "chinese",
  }).with({ year: 2024 }).monthCode, // "M06L" doesn't exist in 2024, should be "M06"
);

Actual results:

console output is M08 M07

Expected results:

console output should be M07 M06 according to https://github.com/tc39/proposal-intl-era-monthcode/pull/47

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The Bugbug bot thinks this bug should belong to the 'Core::JavaScript: Standard Library' component, and is moving the bug to that component. Please correct in case you think the bot is wrong.