RFR: 8159337: Introduce a method in Locale class to return the language tags as per RFC 5646 convention [v4]

[Roger Riggs]

On Tue, 2 May 2023 21:42:09 GMT, Justin Lu <jlu at openjdk.org> wrote:

>> Please review this PR which adds the method `caseFoldLanguageTag(String languageTag)` to java.util.Locale.
>> 
>> This method case folds a language tag to adhere to _[section 2.1.1. Formatting of Language Tags of RFC5646](https://www.rfc-editor.org/rfc/rfc5646.html#section-2.1)_. This format is defined as _"All subtags, including extension and private use subtags, use lowercase letters with two exceptions: two-letter and four-letter subtags that neither appear at the start of the tag nor occur after singletons.  Such two-letter subtags are all uppercase ... and four-letter subtags are titlecase."_.
>> 
>> 
>> In order to match the behavior of existing language tag related Locale methods, this method matches the 2.1.1 RFC5646 specification with the following **exceptions**:
>> - Will not case fold variant subtags
>> - Will not case fold private use subtags prefixed by "lvariant"
>> 
>> As an example, `caseFoldLanguageTag("ja-kana-jp-x-lvariant-Oracle-JDK-Standard-Edition")` returns _"ja-Kana-JP-x-lvariant-Oracle-JDK-Standard-Edition"_. Further examples can be seen in the test file.
>
> Justin Lu has updated the pull request incrementally with four additional commits since the last revision:
> 
>  - Review comment: Replace wellFormed with parseSts to pass errorMsg to exception
>  - Review comment: Adjust method names
>  - Review comment: Use assertThrows and correct IAE to ILE
>  - Review comment: improve legacy_tags id

src/java.base/share/classes/sun/util/locale/LanguageTag.java line 34:

> 32: package sun.util.locale;
> 33: 
> 34: import java.util.*;

Wild card imports are discouraged. It may be useful to update your ide settings to avoid automatic conversions.

src/java.base/share/classes/sun/util/locale/LanguageTag.java line 423:

> 421:         }
> 422:         // Non-legacy tags
> 423:         StringBuilder bldr = new StringBuilder();

Presize the StringBuilder with the current length to avoid a reallocation.

src/java.base/share/classes/sun/util/locale/LanguageTag.java line 429:

> 427:         boolean privUseVarFound = false;
> 428:         for (int i = 0; i < subtags.length; i++) {
> 429:             if (privUseVarFound) {

The following block of code might be easier to read if subtags[i] was put in a local.

src/java.base/share/classes/sun/util/locale/LanguageTag.java line 446:

> 444:                 } else if (subtags[i].equals(PRIVUSE_VARIANT_PREFIX)) {
> 445:                     privUseVarFound = true;
> 446:                 }

These flags can become true but inside the loop cannot become false again.
Is that correct?  For example, I think there can be multiple extension singletons.

test/jdk/java/util/Locale/CaseFoldLanguageTagTest.java line 75:

> 73: 
> 74:     private static Stream<Arguments> wellFormedTags() {
> 75:         return Stream.of(

There are no test cases with multiple singleton extensions either as valid or invalid tests.

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PR Review Comment: https://git.openjdk.org/jdk/pull/13679#discussion_r1184028514
PR Review Comment: https://git.openjdk.org/jdk/pull/13679#discussion_r1184130544
PR Review Comment: https://git.openjdk.org/jdk/pull/13679#discussion_r1184133074
PR Review Comment: https://git.openjdk.org/jdk/pull/13679#discussion_r1184143730
PR Review Comment: https://git.openjdk.org/jdk/pull/13679#discussion_r1184159147