OPENNLP-509 opennlp.tools.parser.Parse.getParent() returning incorrec…

…t object

- adds `setParents(..)` calls in `AbstractBottomUpParser#parse(Parse tokens, int numParses)` which now set the hierarchical (back) references that were missing before
- adds test to verify that a processed Parse instance's parent references are populated and _not_ `null`

opennlp-tools/src/main/java/opennlp/tools/parser/AbstractBottomUpParser.java

@@ -338,15 +338,30 @@ else if (1 == derivationStage) {
       odh = ndh;
     }
     if (completeParses.size() == 0) {
+      if (guess != null) {
+        setParents(guess);
+        for (Parse childGuess: guess.getChildren()) {
+          setParents(childGuess);
+        }
+      }
       return new Parse[] {guess};
     }
     else if (numParses == 1) {
-      return new Parse[] {completeParses.first()};
+      Parse best = completeParses.first();
+      setParents(best);
+      for (Parse childBest: best.getChildren()) {
+        setParents(childBest);
+      }
+      return new Parse[] {best};
     }
     else {
       List<Parse> topParses = new ArrayList<>(numParses);
       while (!completeParses.isEmpty() && topParses.size() < numParses) {
         Parse tp = completeParses.first();
+        setParents(tp);
+        for (Parse childTp: tp.getChildren()) {
+          setParents(childTp);
+        }
         completeParses.remove(tp);
         topParses.add(tp);
         //parses.remove(tp);

opennlp-tools/src/test/java/opennlp/tools/parser/AbstractParserModelTest.java

@@ -91,6 +91,57 @@ void testParsing(String input, String reference) {
     Assertions.assertNotNull(s);
   }
 
+  /*
+   * Verifies / addresses OPENNLP-509
+   * See: https://issues.apache.org/jira/projects/OPENNLP/issues/OPENNLP-509
+   */
+  @Test
+  void testParsingCheckParentReferencesArePopulated() {
+    // fixtures
+    final String sent = "Martin is testing.";
+    // prepare
+    List<String> tokens = Arrays.asList(WhitespaceTokenizer.INSTANCE.tokenize(sent));
+    String text = String.join(" ", tokens);
+
+    Parse sentP = new Parse(text, new Span(0, text.length()),
+            AbstractBottomUpParser.INC_NODE, 0, null);
+    int start = 0;
+    int i = 0;
+    for (Iterator<String> ti = tokens.iterator(); ti.hasNext(); i++) {
+      String tok = ti.next();
+      sentP.insert(new Parse(text, new Span(start, start + tok.length()),
+              AbstractBottomUpParser.TOK_NODE, 0, i));
+      start += tok.length() + 1;
+    }
+
+    Parser parser = ParserFactory.create(getModel());
+    Assertions.assertNotNull(parser);
+
+    // Verifies parents of top-k parses (k=2)
+    Parse[] parses = parser.parse(sentP, 2);
+    Assertions.assertNotNull(parses);
+    for (Parse parent : parses) {
+      checkParentsEqual(parent);
+    }
+  }
+
+  /*
+   * Recursively traverses the parse tree and verifies parent references are populated.
+   */
+  private void checkParentsEqual(Parse parent) {
+    for (Parse child : parent.getChildren()) {
+      Parse cParent = child.getParent();
+      // System.out.println(cParent.toStringPennTreebank() " --- type: " cParent.getType());
+      if (AbstractBottomUpParser.TOK_NODE.equals(child.getType())) {
+        return; // found a leaf node: stopping recursion
+      }
+      Assertions.assertEquals(parent, cParent);
+      if (cParent.getChildren() != null) {
+        checkParentsEqual(child);
+      }
+    }
+  }
+
   /*
    * Verifies changes in OPENNLP-1330 and addresses follow-up OPENNLP-1333
    * See: https://issues.apache.org/jira/projects/OPENNLP/issues/OPENNLP-1333