msfroh commented on code in PR #14350:
URL: https://github.com/apache/lucene/pull/14350#discussion_r2002184400
##########
lucene/core/src/java/org/apache/lucene/util/automaton/CaseFolding.java:
##########
@@ -743,4 +743,42 @@ static int[] lookupAlternates(int codepoint) {
return alts;
}
+
+ /**
+ * Folds the case of the given character according to {@link
Character#toLowerCase(int)}, but with
+ * exceptions if the turkic flag is set.
+ *
+ * @param codepoint to code point for the character to fold
+ * @param turkic if true, then apply tr/az folding rules
+ * @return the folded character
+ */
+ static int foldCase(int codepoint, boolean turkic) {
+ if (turkic) {
+ if (codepoint == 0x00130) { // İ [LATIN CAPITAL LETTER I WITH DOT ABOVE]
+ return 0x00069; // i [LATIN SMALL LETTER I]
+ } else if (codepoint == 0x000049) { // I [LATIN CAPITAL LETTER I]
+ return 0x00131; // ı [LATIN SMALL LETTER DOTLESS I]
+ }
+ }
+ return Character.toLowerCase(codepoint);
Review Comment:
Got it.
Checking https://www.unicode.org/Public/16.0.0/ucd/CaseFolding.txt, indeed I
can see those entries:
```
03A3; C; 03C3; # GREEK CAPITAL LETTER SIGMA
...
03C2; C; 03C3; # GREEK SMALL LETTER FINAL SIGMA
```
Ideally, I'd love to just use those folding rules.
I could get them from `UCharacter.foldCase(int, bool)`, but that involves
pulling in icu4j as a dependency, which is an extra 12MB jar.
Would it be worthwhile to write a generator that pulls
https://www.unicode.org/Public/16.0.0/ucd/CaseFolding.txt (updated to whatever
the current Unicode spec is) and generates a `foldCase` method that's
functionally equivalent to `UCharacter.foldcase(int, bool)`?
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