LUCENE-9721: Hunspell: disallow ONLYINCOMPOUND suffixes at the very end of compound words (#2294)

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

@@ -568,6 +568,12 @@ final class Stemmer {
       if (context != allowed && !dictionary.hasFlag(append, dictionary.compoundPermit, scratch)) {
         return false;
       }
+      if (context == WordContext.COMPOUND_END
+          && !isPrefix
+          && !previousWasPrefix
+          && dictionary.hasFlag(append, dictionary.onlyincompound, scratch)) {
+        return false;
+      }
     }
 
     if (recursionDepth == 0) {

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

@@ -152,6 +152,10 @@ public class SpellCheckerTest extends StemmerTestBase {
     doTest("compoundrule8");
   }
 
+  public void testDisallowCompoundOnlySuffixesAtTheVeryEnd() throws Exception {
+    doTest("onlyincompound2");
+  }
+
   public void testGermanCompounding() throws Exception {
     doTest("germancompounding");
   }

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/onlyincompound2.aff

@@ -0,0 +1,12 @@
+# affixes only in compounds (see also fogemorpheme example)
+ONLYINCOMPOUND O
+COMPOUNDFLAG A
+COMPOUNDPERMITFLAG P
+
+SFX B Y 1
+SFX B 0 s/OP .
+
+# obligate fogemorpheme by forbidding the stem (0) in compounds
+
+CHECKCOMPOUNDPATTERN 1
+CHECKCOMPOUNDPATTERN 0/B /A

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/onlyincompound2.dic

@@ -0,0 +1,3 @@
+2
+foo/A
+pseudo/AB

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/onlyincompound2.good

@@ -0,0 +1,3 @@
+foo
+foopseudo
+pseudosfoo

lucene/analysis/common/src/test/org/apache/lucene/analysis/hunspell/onlyincompound2.wrong

@@ -0,0 +1,3 @@
+pseudos
+foopseudos
+pseudofoo