<i18n dev> RFR: 8368981: Case Fold Locale Legacy Tags On Demand

[Naoto Sato]

On Wed, 1 Oct 2025 21:11:53 GMT, Justin Lu <jlu at openjdk.org> wrote:

> Please review this PR which case folds grandfathered BCP47 tags on demand. (Instead of keeping the case compliant versions stored.)
> 
> This facilitates the cleanup of the `LEGACY` map (which contains a String to String Array mapping). The 2D String array, creation and populating of the  `LEGACY` map, as well as lower case folding of the legacy tags can now be removed from the static block of _sun.util.locale.LanguageTag_.
> 
> Legacy tags are a small subset compared to the entire set of valid BCP47 tags. Reducing the cost for supporting them would be ideal. Instead, legacy tags can now be checked against and folded on demand via a switch statement.
> 
> The commented grandfathered syntax is removed because the values themselves already exist as code, and the exact case can be found in the provided RFC link.

Looks good. Some minor comments follow

src/java.base/share/classes/sun/util/locale/LanguageTag.java line 111:

> 109: 
> 110:         // Check if the tag is a legacy tag
> 111:         var modern = legacyToModern(LocaleUtils.toLowerString(languageTag));

I'd use "preferred" instead of "modern", as it is used in the RFC.

test/jdk/java/util/Locale/CaseFoldLanguageTagTest.java line 112:

> 110:                 "zh-guoyu",
> 111:                 "i-pwn",
> 112:                 "i-mingo"

Is this intentionally randomized? Otherwise I would like it to be sorted.

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PR Review: https://git.openjdk.org/jdk/pull/27596#pullrequestreview-3291289066
PR Review Comment: https://git.openjdk.org/jdk/pull/27596#discussion_r2396010744
PR Review Comment: https://git.openjdk.org/jdk/pull/27596#discussion_r2396013611