Bug 275095 – [JSC] Fix behavior of `Intl.DurationFormat` for negative values

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Sosuke Suzuki]

The current implementation of `Intl.DurationFormat` is incorrect in two ways regarding how it handles negative values:
    
    1. When the values of multiple units are negative, display `-` only for the largest unit.
    For example, the duration `{ years: -1, months: -2 }` should be formatted as `"-1 years, 2 months"`.
    According to the spec[1], this behavior is controlled by the `signDisplayed` variable (initially
    set to true). This variable is set to false once any unit is formatted.
    
    2. Implement the DurationSign abstract operation [2] to display negative zero.
    For example, the duration `{ hours: 0, seconds: -1 }` should be formatted as `"-0 hours, 1 second"`.
    This is described in section 4.f.iii.3.b of the spec [1] as follows:
    
        > b. If value is 0 and DurationSign(duration.[[Years]], duration.[[Months]], duration.[[Weeks]], duration.[[Days]], duration.[[Hours]], duration.[[Minutes]], duration.[[Seconds]], duration.[[Milliseconds]], duration.[[Microseconds]], duration.[[Nanoseconds]]) is -1, then
        >     i. Set value to negative-zero.
    
    The `partitionDurationFormatPattern` function [3] in the `harness/testintl.js` of test262 describes
    a similar process to the changes in this patch.
    
    [1]: https://tc39.es/proposal-intl-duration-format/#sec-partitiondurationformatpattern
    [2]: https://tc39.es/proposal-intl-duration-format/#sec-durationsign
    [3]: https://github.com/tc39/test262/blob/249657722525cc8e43b1ddb91f8df0b4b011fcf6/harness/testIntl.js#L2649-L2662

[Sosuke Suzuki]

Pull Request: https://github.com/WebKit/WebKit/pull/29489

[Radar WebKit Bug Importer]

<rdar://problem/129561747>

[EWS]

Committed 279902@main (3f74bba5c41c): <https://commits.webkit.org/279902@main>

Reviewed commits have been landed. Closing PR #29489 and removing active labels.