Issue #21162 has been reported by headius (Charles Nutter). ---------------------------------------- Bug #21162: Regexp casefold mismatch for latin1 supplemental chars https://bugs.ruby-lang.org/issues/21162 * Author: headius (Charles Nutter) * Status: Open * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- Originally reported to joni repo with a possible fix here: https://github.com/jruby/joni/pull/20 From that PR:
When a character is less than or equal to single byte size (0xff), yet it takes more than 1 byte in the current encoding, the case folding code incorrectly put it in bitset instead of code range. As a result, for utf8 encoding, casefold works incorrectly on characters in range \u0080 to \u00ff (latin1 supplement).
Before fix:
"\u00c2" [\u00e0-\u00e5] returns false "\u00c2" [\u00e2] returns false "\u00c2" \u00e2 returns true
As a Ruby example: ``` $ ruby -v -e 'p(/[\u00e0-\u00e5]/i =~ "\u00c2")' ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [arm64-darwin24] nil ``` The PR above was rebased in https://github.com/jruby/joni/pull/85. When that patch is incorporated into JRuby, it behaves as expected: ``` $ ruby -v -e 'p(/[\u00e0-\u00e5]/i =~ "\u00c2")' jruby 10.0.0.0-SNAPSHOT (3.4.0) 2025-02-27 c0e5008419 OpenJDK 64-Bit Server VM 21.0.5+11-LTS on 21.0.5+11-LTS +indy +jit [arm64-darwin] 0 ``` This bug may affect other casefold situations. As I am not very familiar with this code in CRuby (other than from maintaining the port in joni) I would like others to evaluate this fix and help find other places it is needed. -- https://bugs.ruby-lang.org/