<i18n dev> RFR: 8225641: Calendar.roll(int field) does not work correctly for WEEK_OF_YEAR [v6]

[Naoto Sato]

On Thu, 30 Mar 2023 21:33:16 GMT, Justin Lu <jlu at openjdk.org> wrote:

>> This PR fixes the bug which occurred when `Calendar.roll(WEEK_OF_YEAR)` rolled into a minimal first week with an invalid `WEEK_OF_YEAR` and `DAY_OF_WEEK` combo.
>> 
>> For example, Rolling _Monday, 30 December 2019_ by 1 week produced _Monday, 31 December 2018_, which is incorrect. This is because `WEEK_OF_YEAR` is rolled from 52 to 1, and the original `DAY_OF_WEEK` is 1. However, there is no Monday in week 1 of 2019. This is exposed when a future method calls `Calendar.complete()`, which eventually calculates a `fixedDate` with the invalid `WEEK_OF_YEAR` and `DAY_OF_WEEK` combo.
>> 
>> To prevent this, a check is added for rolls into week 1, which determines if the first week is minimal. If it is indeed minimal, then it is checked if  `DAY_OF_WEEK` exists in that week, if not, `WEEK_OF_YEAR` must be incremented by one.
>> 
>> After the fix, Rolling _Monday, 30 December 2019_ by 1 week produces _Monday, 7 January 2019_
>
> Justin Lu has updated the pull request incrementally with two additional commits since the last revision:
> 
>  - dayInMinWeek should range check input and throw exception
>  - Tweak static cal builder

src/java.base/share/classes/java/util/GregorianCalendar.java line 3025:

> 3023:         if (endDay > 7 || endDay < 1 || startDay > 7 || startDay < 1) {
> 3024:             throw new IllegalArgumentException("Start day or end day is not " +
> 3025:                     "a valid day of the week");

Sorry, I take my previous comment back. I think we can simply rely on the return value from `getFirstDayOfWeek()` as it is well-checked, so no need to check the input here. Otherwise the thrown IAE woudl have to end up in `add()/roll()` public methods, which cannot be spec'ed with these internal arguments.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13031#discussion_r1153877382