Fix cyclic references handling in struct tree parent

DEVSIX-8616

Author: guustysebie

kernel/src/main/java/com/itextpdf/kernel/pdf/tagging/StructureTreeCopier.java

@@ -43,6 +43,8 @@ This file is part of the iText (R) project.
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+
+import com.itextpdf.kernel.pdf.tagutils.TagTreeIterator;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
@@ -629,11 +631,14 @@ private static PdfDictionary getTopmostParent(PdfMcr mcr) {
     }
 
     private static List<PdfDictionary> retrieveParents(PdfMcr mcr, boolean all) {
-        List<PdfDictionary> parents = new ArrayList<>();
-        IStructureNode firstParent = mcr.getParent();
+        final Set<PdfDictionary> parents = new LinkedHashSet<>();
+        final IStructureNode firstParent = mcr.getParent();
         PdfDictionary previous = null;
         PdfDictionary current = firstParent instanceof PdfStructElem ? ((PdfStructElem) firstParent).getPdfObject() : null;
-        while (current != null && !PdfName.StructTreeRoot.equals(current.getAsName(PdfName.Type))) {
+
+        while (current != null
+               && !PdfName.StructTreeRoot.equals(current.getAsName(PdfName.Type))
+               && !parents.contains(current)) {
             if (all) {
                 parents.add(current);
             }
@@ -643,7 +648,7 @@ private static List<PdfDictionary> retrieveParents(PdfMcr mcr, boolean all) {
         if (!all) {
             parents.add(previous);
         }
-        return parents;
+        return new ArrayList<>(parents);
     }
 
     static class LastClonedAncestor {

kernel/src/test/java/com/itextpdf/kernel/utils/PdfMergerTest.java

@@ -162,6 +162,22 @@ public void mergeDocumentTest02() throws IOException, InterruptedException {
         Assertions.assertNull(new CompareTool().compareByContent(resultFile, sourceFolder + "cmp_mergedResult02.pdf", destinationFolder, "diff_"));
     }
 
+    @Test
+    public void mergeDocumentWithCycleTagReferenceTest() throws IOException, InterruptedException {
+        String filename1 = sourceFolder + "doc1.pdf";
+        String filename2 = sourceFolder + "pdfWithCycleRefInParentTag.pdf";
+        String resultFile = destinationFolder + "pdfWithCycleRefInParentTag.pdf";
+        try (PdfDocument pdfDocument1 = new PdfDocument(new PdfReader(filename2));
+             PdfDocument pdfDocument2 = new PdfDocument(new PdfReader(filename1),
+                     CompareTool.createTestPdfWriter(resultFile).setSmartMode(true));) {
+            PdfMerger merger = new PdfMerger(pdfDocument2);
+            merger.merge(pdfDocument1, 1, pdfDocument1.getNumberOfPages());
+        }
+        Assertions.assertNull(
+                new CompareTool().compareByContent(resultFile, sourceFolder + "cmp_pdfWithCycleRefInParentTag.pdf",
+                        destinationFolder, "diff_"));
+    }
+
     @Test
     @LogMessages(messages = {
             @LogMessage(messageTemplate = IoLogMessageConstant.SOURCE_DOCUMENT_HAS_ACROFORM_DICTIONARY)