RFR: 8360459: UNICODE_CASE and character class with non-ASCII range does not match ASCII char [v2]

[Naoto Sato]

On Mon, 14 Jul 2025 07:54:31 GMT, Xueming Shen <sherman at openjdk.org> wrote:

>> Regex class should conform to **_Level 1_** of [Unicode Technical Standard #18: Unicode Regular Expressions](http://www.unicode.org/reports/tr18/), plus RL2.1 Canonical Equivalents and RL2.2 Extended Grapheme Clusters.
>> 
>> This PR primarily addresses conformance with RL1.5: Simple Loose Matches, which requires that simple case folding be applied to literals and (optionally) to character classes. When applied to character classes, each class is expected to be closed under simple case folding. See the standard for a detailed explanation of what it means for a class to be “closed.”
>> 
>> To conform with Level 1 of UTS #18, specifically RL1.5: Simple Loose Matches, simple case folding must be applied to literals and (optionally) to character classes. When applied to character classes, each character class is expected to **be closed under simple case folding**.  See the standard for the detailed explanation and example of "closed".
>> 
>> **RL1.5 states**: 
>> 
>> To meet this requirement, an implementation that supports case-sensitive matching should
>> 
>>     1. Provide at least the simple, default Unicode case-insensitive matching, and
>>     2. Specify which character properties or constructs are closed under the matching.
>> 
>> **In the Pattern implementation**, 5 types of constructs may be affected by case sensitivity:
>> 
>>     1. back-refs
>>     2. string slices (sequences)
>>     3. single character,
>>     4. character families (Unicode Properties ...), and
>>     5. character class ranges
>> 
>> **Note**: Single characters and families may appear independently or within a character class.
>> 
>> For case-insensitive (loose) matching, the implementation already applies Character.toUpperCase() and Character.toLowerCase() to **both the pattern and the input string** for back-refs, slices, and single characters. This effectively makes these constructs closed under case folding.
>> 
>> This has been verified in the newly added test case **_test/jdk/java/util/regex/CaseFoldingTest.java_**.
>> 
>> For example:
>> 
>> Pattern.compile("(?ui)\u017f").matcher("S").matches().      => true
>> Pattern.compile("(?ui)[\u017f]").matcher("S").matches()    => true
>> 
>> The character properties (families)  are not "closed" and should remain unchanged. This is acceptable per RL1.5, if the  behavior is clearly specified (TBD: update javadoc to reflect this).
>> 
>> **Current Non-Conformance: Character Class Ranges**, as reported in the original bug report.
>> 
>> Pattern.compile("(?ui)[\u017f-\u...
>
> Xueming Shen has updated the pull request incrementally with one additional commit since the last revision:
> 
>   update to address the review comments

Looks good. Thanks for adding case folding support which is long overdue 🙂
Since this is adding a new support for casefolding for character class ranges, I think CSR and a release note should be considered.

make/jdk/src/classes/build/tools/generatecharacter/CaseFolding.java line 73:

> 71:             StandardOpenOption.CREATE, StandardOpenOption.TRUNCATE_EXISTING);
> 72:     }
> 73: }

Needs a NL at the end

test/jdk/java/util/regex/CaseFoldingTest.java line 30:

> 28:  * @library /lib/testlibrary/java/lang
> 29:  * @author Xueming Shen
> 30:  * @run testng CaseFoldingTest

Since this is a new test, I think we prefer junit over testng

test/jdk/java/util/regex/CaseFoldingTest.java line 61:

> 59: 
> 60:         var results = Files.readAllLines(UCDFiles.CASEFOLDING)
> 61:             .stream()

Files.lines() may be more concise

test/jdk/lib/testlibrary/java/lang/UCDFiles.java line 59:

> 57:         UCD_DIR.resolve("emoji").resolve("emoji-data.txt");
> 58:     public static Path CASEFOLDING =
> 59:         UCD_DIR.resolve("CaseFolding.txt");

Copyright year -> 2025

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PR Review: https://git.openjdk.org/jdk/pull/26285#pullrequestreview-3017279774
PR Review Comment: https://git.openjdk.org/jdk/pull/26285#discussion_r2205510750
PR Review Comment: https://git.openjdk.org/jdk/pull/26285#discussion_r2205508784
PR Review Comment: https://git.openjdk.org/jdk/pull/26285#discussion_r2205517080
PR Review Comment: https://git.openjdk.org/jdk/pull/26285#discussion_r2205521609