LUCENE-9786: Hunspell suggestions: try moving the last character into the middle (#2399)

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

@@ -245,11 +245,14 @@ class ModifyingSuggester {
 
   private void tryMovingChar(String word) {
     for (int i = 0; i < word.length(); i++) {
+      String prefix = word.substring(0, i);
       for (int j = i + 2; j < word.length() && j <= i + MAX_CHAR_DISTANCE; j++) {
-        String prefix = word.substring(0, i);
         trySuggestion(prefix + word.substring(i + 1, j) + word.charAt(i) + word.substring(j));
         trySuggestion(prefix + word.charAt(j) + word.substring(i, j) + word.substring(j + 1));
       }
+      if (i < word.length() - 1) {
+        trySuggestion(prefix + word.substring(i + 1) + word.charAt(i));
+      }
     }
   }
 

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

@@ -13,7 +13,7 @@
 
 # switch off ngram suggestion for testing
 MAXNGRAMSUGS 0
-TRY -
+TRY -b
 REP 2
 REP alot a_lot
 REP inspite in_spite

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

@@ -13,3 +13,6 @@ permanent-vacation/?
 in
 spite
 inspire
+Saiph
+sahib
+ship

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/sug.sug

@@ -12,4 +12,4 @@ Gandhi
 McDonald
 permanent
 in, in a
-
+Saiph, Ship, Sahib

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

@@ -13,4 +13,5 @@ Mcdonald
 permqnent
 permanent-vacation
 permqnent-vacation
-ina
+ina
+Sahip