RFR: 8357275: Locale.Builder.setLanguageTag should explicitly state extlangs are allowed

[Naoto Sato]

On Mon, 19 May 2025 23:50:59 GMT, Justin Lu <jlu at openjdk.org> wrote:

>> src/java.base/share/classes/java/util/Locale.java line 2792:
>> 
>>> 2790:          * tag). {@code languageTag} may contain up to three extlang subtags.
>>> 2791:          + For such occurrences, the first extlang subtag is used as the language,
>>> 2792:          * and the primary language subtag and other extlang subtags are ignored.
>> 
>> Should we throw an exeption here? I had an impression that the new description actually contradicts to the previous sentense, which asserts exception on ill-formed tag.
>
> An exception is thrown when more than three extlang subtags are provided (ill-formed). The new wording is when an allowed amount of extlang subtags are provided (not ill-formed). For example,
> 
> `new Locale.Builder().setLanguageTag("zh-yue-gan-cmn-czh-CN").build()` // throws
> `new Locale.Builder().setLanguageTag("zh-yue-gan-cmn-CN").build()` // ==> yue_CN
> 
> i.e. if one to three extlang subtags occur, discard extras. If more than 3 occur, then it is ill-formed, and the method is already specified to throw on ill-formed tags. (Edit: Forgot to adjust the example)

OK. I would add these examples here too, which may be more helpful.

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PR Review Comment: https://git.openjdk.org/jdk/pull/25309#discussion_r2096650651