rmuir commented on code in PR #14350:
URL: https://github.com/apache/lucene/pull/14350#discussion_r2000536590
##########
lucene/core/src/java/org/apache/lucene/util/automaton/CaseFolding.java:
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@@ -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:
For real case folding we have to do more than this. it is a simple 1-1
mapping but e.g. `Σ`, `σ`, and `ς`, will all fold to σ. Whereas toLowerCase(ς)
= ς. Because it is already in lower-case, just in final-form. This is just an
example. To see more, compare your function against ICU
UCharacter.foldCase(int, bool) across all of unicode.
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