LUCENE-9690: Hunspell: support special title-case for words with apostrophe (#2235)

Author: donnerpeter

lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/SpellChecker.java

@@ -74,6 +74,10 @@ private boolean checkCaseVariants(char[] wordChars, WordCase wordCase) {
       if (checkWord(caseVariant, wordChars.length, true)) {
         return true;
       }
+      char[] aposCase = stemmer.capitalizeAfterApostrophe(caseVariant, wordChars.length);
+      if (aposCase != null && checkWord(aposCase, aposCase.length, true)) {
+        return true;
+      }
     }
     return checkWord(stemmer.caseFoldLower(caseVariant, wordChars.length), wordChars.length, true);
   }

lucene/analysis/common/src/java/org/apache/lucene/analysis/hunspell/Stemmer.java

@@ -98,6 +98,10 @@ public List<CharsRef> stem(char[] word, int length) {
     List<CharsRef> list = doStem(word, length, false);
     if (wordCase == WordCase.UPPER) {
       caseFoldTitle(word, length);
+      char[] aposCase = capitalizeAfterApostrophe(titleBuffer, length);
+      if (aposCase != null) {
+        list.addAll(doStem(aposCase, length, true));
+      }
       list.addAll(doStem(titleBuffer, length, true));
     }
     if (wordCase == WordCase.UPPER || wordCase == WordCase.TITLE) {
@@ -138,6 +142,23 @@ char[] caseFoldLower(char[] word, int length) {
     return lowerBuffer;
   }
 
+  // Special prefix handling for Catalan, French, Italian:
+  // prefixes separated by apostrophe (SANT'ELIA -> Sant'+Elia).
+  char[] capitalizeAfterApostrophe(char[] word, int length) {
+    for (int i = 1; i < length - 1; i++) {
+      if (word[i] == '\'') {
+        char next = word[i + 1];
+        char upper = Character.toUpperCase(next);
+        if (upper != next) {
+          char[] copy = ArrayUtil.copyOfSubArray(word, 0, length);
+          copy[i + 1] = Character.toUpperCase(upper);
+          return copy;
+        }
+      }
+    }
+    return null;
+  }
+
   List<CharsRef> doStem(char[] word, int length, boolean caseVariant) {
     List<CharsRef> stems = new ArrayList<>();
     IntsRef forms = dictionary.lookupWord(word, 0, length);

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/SpellCheckerTest.java

@@ -26,6 +26,11 @@
 import org.junit.Test;
 
 public class SpellCheckerTest extends StemmerTestBase {
+  @Test
+  public void allcaps() throws Exception {
+    doTest("allcaps");
+  }
+
   @Test
   public void i53643_numbersWithSeparators() throws Exception {
     doTest("i53643");

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/TestAllCaps.java

@@ -28,6 +28,8 @@ public static void beforeClass() throws Exception {
   public void testGood() {
     assertStemsTo("OpenOffice.org", "OpenOffice.org");
     assertStemsTo("UNICEF's", "UNICEF");
+    assertStemsTo("L'Afrique", "Afrique");
+    assertStemsTo("L'AFRIQUE", "Afrique");
 
     // Hunspell returns these title-cased stems, so for consistency we do, too
     assertStemsTo("OPENOFFICE.ORG", "Openoffice.org");

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/allcaps.aff

@@ -3,3 +3,6 @@ WORDCHARS '.
 
 SFX S N 1
 SFX S   0     's      .
+
+PFX L N 1
+PFX L   0     L'

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/allcaps.dic

@@ -1,3 +1,4 @@
 2
 OpenOffice.org
 UNICEF/S
+Afrique/L

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/allcaps.good

@@ -0,0 +1,6 @@
+OpenOffice.org
+OPENOFFICE.ORG
+UNICEF's
+UNICEF'S
+L'AFRIQUE
+L'Afrique

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/allcaps.wrong

@@ -0,0 +1,3 @@
+Openoffice.org
+Unicef
+Unicef's