LUCENE-9775: Hunspell: make FORCEUCASE work when the first compound word is inherently title-case (#2375)

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

@@ -94,7 +94,7 @@ class CheckCompoundPattern {
   CharsRef expandReplacement(CharsRef word, int breakPos) {
     if (replacement != null && charsMatch(word, breakPos, replacement)) {
       return new CharsRef(
-          word.subSequence(0, breakPos)
+          new String(word.chars, 0, word.offset + breakPos)
               + endChars
               + beginChars
               + word.subSequence(breakPos + replacement.length(), word.length));

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

@@ -171,6 +171,10 @@ public class Hunspell {
 
   private boolean checkCompounds(CharsRef word, WordCase originalCase, CompoundPart prev) {
     if (prev != null && prev.index > dictionary.compoundMax - 2) return false;
+    if (prev == null && word.offset != 0) {
+      // we check the word's beginning for FORCEUCASE and expect to find it at 0
+      throw new IllegalArgumentException();
+    }
 
     int limit = word.length - dictionary.compoundMin + 1;
     for (int breakPos = dictionary.compoundMin; breakPos < limit; breakPos++) {
@@ -231,7 +235,7 @@ public class Hunspell {
     if (lastRoot != null
         && !dictionary.hasFlag(lastRoot.entryId, dictionary.forbiddenword)
         && !(dictionary.checkCompoundDup && prev.root.equals(lastRoot))
-        && !hasForceUCaseProblem(lastRoot, originalCase)
+        && !hasForceUCaseProblem(lastRoot, originalCase, word.chars)
         && prev.mayCompound(lastRoot, remainingLength, originalCase)) {
       return true;
     }
@@ -240,8 +244,9 @@ public class Hunspell {
     return checkCompounds(tail, originalCase, prev);
   }
 
-  private boolean hasForceUCaseProblem(Root<?> root, WordCase originalCase) {
+  private boolean hasForceUCaseProblem(Root<?> root, WordCase originalCase, char[] wordChars) {
     if (originalCase == WordCase.TITLE || originalCase == WordCase.UPPER) return false;
+    if (originalCase == null && Character.isUpperCase(wordChars[0])) return false;
     return dictionary.hasFlag(root.entryId, dictionary.forceUCase);
   }
 

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

@@ -2,3 +2,4 @@
 foo/C
 bar/C
 baz/CA
+Upper/C

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

@@ -1,3 +1,4 @@
+Foobaz
 foo
 bar
 baz
@@ -5,3 +6,4 @@ foobar
 Foobaz
 foobazbar
 Foobarbaz
+Upperbaz