Bug: Malformed leap month suffix while implementing Chinese calendar

[pattishin]

Browser: Safari 26.4

Polyfill cdn: https://esm.sh/@js-temporal/polyfill

Issue: I'm leveraging this polyfill for a chinese calendar I am implementing to also include the leap year functionality from Temporal. The error I came across was Error: Unexpected leap month suffix: Mo3.

To recreate:

const today = (Temporal.Now.plainDateISO()).toString();
const date = Temporal.PlainDate.from(today);
const chineseDate = date.withCalendar('chinese');

// Calling chineseDate.year, chineseDate.month, chinese.monthCode, chineseDate.monthsInYear recreates the error

It seems like a malformed month code issue stemming from

temporal-polyfill/lib/calendar.ts

Line 777 in ef32041

if (monthExtra !== undefined) throw new RangeError('Unexpected `monthExtra` value');

Any help or direction would be much appreciated!

Screenshots of the error:

[justingrant]

Thanks for reporting this bug. This problem is caused by a change in the underlying ICU and CLDR implementation that Intl.DateTimeFormat uses to source its calendar data.

The problem is fixed in an upstream commit in proposal-temporal but has not yet been migrated into this polyfill repo. It should be fixed soon once we finish migrating all commits over here. Sorry for the inconvenience.

[pattishin]

Oh excellent! Thanks so much! Looking forward to the update. 👍🏼