Firefox: wrong yearOfWeek/weekOfYear for gregory calendar

[o-t-w]

I am basing the correct behaviour based on how the Firefox implementation works.

For the ISO calendar, I would expect, and I get the following results:

const lastDay2029 = Temporal.PlainDate.from('2029-12-31');
console.log(lastDay2029.weekOfYear) // 1
console.log(lastDay2029.yearOfWeek) // 2030

Using the polyfill, I get the same results as those above when using the gregory calendar, whereas in Firefox I get:

const lastDay2029 = Temporal.PlainDate.from('2029-12-31[u-ca=gregory]');
console.log(lastDay2029.weekOfYear) // 53
console.log(lastDay2029.yearOfWeek) // 2029

[Sector6759]

I am basing the correct behaviour based on how the Firefox implementation works.

To me it appears that the Firefox implementation is wrong. December 31, 2029 is a monday, so its ISO week date is 2030-W01-1, as the majority of that week is in the gregorian year 2030. So the issue should be reported to Mozilla, not to @arshaw.

[arshaw]

Both temporal-polyfill and the reference implementation give 1 2030, so it seems like Firefox has a bug as @Sector6759 says. We'd need to figure out the best place to file this with Mozilla.

[arshaw]

I filed a bug here: https://bugzilla.mozilla.org/show_bug.cgi?id=1950162