Polyfill: Hour cycle not correctly set when defaults are used

[anba]

Test case:

console.log(new Temporal.PlainDateTime(2020, 1, 1).toLocaleString("en", {hour12: false}));
console.log(new Temporal.PlainDateTime(2020, 1, 1).toLocaleString("en", {hour12: true}));

console.log(new Temporal.PlainDateTime(2020, 1, 1).toLocaleString("en", {hourCycle: "h23"}));
console.log(new Temporal.PlainDateTime(2020, 1, 1).toLocaleString("en", {hourCycle: "h24"}));
console.log(new Temporal.PlainDateTime(2020, 1, 1).toLocaleString("en", {hourCycle: "h11"}));
console.log(new Temporal.PlainDateTime(2020, 1, 1).toLocaleString("en", {hourCycle: "h12"}));

Actual:

1/1/2020, 12:00:00 AM
1/1/2020, 12:00:00 AM
1/1/2020, 12:00:00 AM
1/1/2020, 12:00:00 AM
1/1/2020, 12:00:00 AM
1/1/2020, 12:00:00 AM

Expected:

1/1/2020, 00:00:00
1/1/2020, 12:00:00 AM
1/1/2020, 00:00:00
1/1/2020, 24:00:00
1/1/2020, 0:00:00 AM
1/1/2020, 12:00:00 AM

[ptomato]

Thanks for pointing this out. I guess it's locale-dependent whether the first line of the expected results should have 00:00:00 or 24:00:00?

I'll submit a PR to make the reference code conform to the spec. However, clearly this was a gap in test262 coverage since it wasn't caught before, so I've added the test262 label to this issue and will keep it open. We should have coverage for PlainTime, PlainDateTime, Instant, and ZonedDateTime formatting.

[anba]

I guess it's locale-dependent whether the first line of the expected results should have 00:00:00 or 24:00:00?

24:00:00 only if a locale had hc24 as its default hour cycle, which no locale has → https://unicode-org.atlassian.net/browse/CLDR-18303.

The second line, for hour12: true, can have either 12:00:00 (all locales except Japanese) or 0:00:00 (Japanese).