<i18n dev> RFR: 8313813: Field sun.util.calendar.CalendarDate#forceStandardTime is never set [v4]

[Justin Lu]

On Fri, 15 Sep 2023 18:54:19 GMT, Justin Lu <jlu at openjdk.org> wrote:

>> Please review this PR which is a continuation of [JDK-6453901](https://bugs.openjdk.org/browse/JDK-6453901) to remove unused code from the _sun.util.Calendar_ classes.
>> 
>> `forceStandardTime` is always false.
>> 
>> In addition, `locale` is never by used by _CalendarDate_ or any inheritors and can be removed.
>> 
>> As a result, _ImmutableGregorianDate_ no longer needs to override the _setLocale_ method and throw UnsupportedOperationException.
>
> Justin Lu has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Clarify implementation after removal of if else block

src/java.base/share/classes/sun/util/calendar/AbstractCalendar.java line 176:

> 174:             //    as 1:30am DT/0:30am ST (before transition)
> 175:             if (zi instanceof ZoneInfo zInfo) {
> 176:                 // Offset value adjusts accordingly depending on DST status of date

Historically, this `if else` has not been touched since the introduction of the class.

The original code has a structure that one can presume follows the logic, if `isStandardTime()`, get a standard offset, otherwise get a day light saving offset. This is not the case. 

The code within the `else` statement is able to retrieve the correct offset if the date is in standard **or** in day light saving time (not just a day light saving offset, as the original code would imply). Consider the following example,


// Where ms is calculated from the date: LA time zone at 3-13-2016 at 4 AM (daylight saving)
zoneOffset = zInfo.getOffsetsByWall(ms, new int[2]); 
// returns the adjusted offset, -25200000 (7 hours)

// Where ms is calculated from the date: LA time zone at 1-13-2016 at 4 AM (standard)
zoneOffset = zInfo.getOffsetsByWall(ms, new int[2]); 
// returns the standard offset, -28800000 (8 hours)

Removing this code is not only safe because `isStandardTime()` is always `false`
- tiers 1-3 clean
- breakpoint within the original `if` never breaks execution for JDK Calendar tests

But we can also feel that the change is not suspicious since the code within the `else` block can produce a standard or daylight offset.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15726#discussion_r1327678366