LUCENE-9732: Hunspell: support dictionary entries starting with slash (#2301)

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

@@ -832,7 +832,7 @@ public class Dictionary {
       if (ch == '\\' && i + 1 < entry.length()) {
         sb.append(entry.charAt(i + 1));
         i++;
-      } else if (ch == '/') {
+      } else if (ch == '/' && i > 0) {
         sb.append(FLAG_SEPARATOR);
       } else if (!shouldSkipEscapedChar(ch)) {
         sb.append(ch);
@@ -902,10 +902,7 @@ public class Dictionary {
         String line;
         while ((line = lines.readLine()) != null) {
           // wild and unpredictable code comment rules
-          if (line.isEmpty()
-              || line.charAt(0) == '/'
-              || line.charAt(0) == '#'
-              || line.charAt(0) == '\t') {
+          if (line.isEmpty() || line.charAt(0) == '#' || line.charAt(0) == '\t') {
             continue;
           }
           line = unescapeEntry(line);

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

@@ -17,13 +17,23 @@
 package org.apache.lucene.analysis.hunspell;
 
 enum WordCase {
+  /** e.g. WORD */
   UPPER,
+
+  /** e.g. Word */
   TITLE,
+
+  /** e.g. word */
   LOWER,
-  MIXED;
+
+  /** e.g. WoRd or wOrd */
+  MIXED,
+
+  /** e.g "-" or "/" or "42" */
+  NEUTRAL;
 
   static WordCase caseOf(char[] word, int length) {
-    boolean startsWithLower = Character.isLowerCase(word[0]);
+    CharCase startCase = charCase(word[0]);
 
     boolean seenUpper = false;
     boolean seenLower = false;
@@ -34,7 +44,7 @@ enum WordCase {
       if (seenUpper && seenLower) break;
     }
 
-    return get(startsWithLower, seenUpper, seenLower);
+    return get(startCase, seenUpper, seenLower);
   }
 
   static WordCase caseOf(CharSequence word) {
@@ -42,7 +52,7 @@ enum WordCase {
   }
 
   static WordCase caseOf(CharSequence word, int length) {
-    boolean startsWithLower = Character.isLowerCase(word.charAt(0));
+    CharCase startCase = charCase(word.charAt(0));
 
     boolean seenUpper = false;
     boolean seenLower = false;
@@ -53,14 +63,19 @@ enum WordCase {
       if (seenUpper && seenLower) break;
     }
 
-    return get(startsWithLower, seenUpper, seenLower);
+    return get(startCase, seenUpper, seenLower);
   }
 
-  private static WordCase get(boolean startsWithLower, boolean seenUpper, boolean seenLower) {
-    if (!startsWithLower) {
-      return !seenLower ? UPPER : !seenUpper ? TITLE : MIXED;
+  private static WordCase get(CharCase startCase, boolean seenUpper, boolean seenLower) {
+    if (seenLower && seenUpper) return MIXED;
+    switch (startCase) {
+      case LOWER:
+        return seenUpper ? MIXED : LOWER;
+      case UPPER:
+        return !seenLower ? UPPER : TITLE;
+      default:
+        return seenLower ? LOWER : seenUpper ? UPPER : NEUTRAL;
     }
-    return seenUpper ? MIXED : LOWER;
   }
 
   private static CharCase charCase(char c) {

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

@@ -25,11 +25,16 @@ public class TestEscaped extends StemmerTestBase {
   }
 
   public void testStemming() {
+    assertStemsTo("/", "/");
     assertStemsTo("works", "work");
     assertStemsTo("work", "work");
     assertStemsTo("R2/D2", "R2/D2", "R2/d2");
     assertStemsTo("R2/D2s", "R2/D2");
     assertStemsTo("N/A", "N/A");
     assertStemsTo("N/As");
+
+    assertStemsTo("/", "/");
+    assertStemsTo("/a", "/a");
+    assertStemsTo("//");
   }
 }

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

@@ -1,4 +1,6 @@
-3
+5
+/
+/a
 work/A
 R2\/D2/A
 N\/A