fix(java): reproduce silent Set child-loss for package-private nodes

java/fory-core/src/test/java/org/apache/fory/codegen/pkgprivate/PackagePrivateCyclicSetChildLossTest.java

@@ -0,0 +1,147 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.fory.codegen.pkgprivate;
+
+import static org.testng.Assert.assertEquals;
+import static org.testng.Assert.assertTrue;
+
+import java.io.Serializable;
+import java.util.ArrayList;
+import java.util.EnumMap;
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedHashSet;
+import java.util.List;
+import java.util.Map;
+import java.util.Objects;
+import java.util.Set;
+import org.apache.fory.Fory;
+import org.apache.fory.ThreadSafeFory;
+import org.testng.annotations.Test;
+
+/**
+ * Regression test: a wide fan-out (one parent, many children) cyclic graph of package-private
+ * nodes silently loses entries from a {@code Set<PackagePrivateType>} field during
+ * deserialization - no exception is thrown, so unlike {@link PackagePrivateMapKeyTest} (which
+ * catches the codegen CompileException for this same field shape) this defect only surfaces as
+ * missing data.
+ *
+ * <p>Reproduced from a production graph with 100+ children under one parent node; the
+ * child->parent edge (an EnumMap-keyed back-reference) survives the round trip intact, but the
+ * parent->child edge (a plain HashSet) loses a handful of entries. Both edges are set together,
+ * atomically, at construction time, so the source object graph itself is never inconsistent -
+ * the asymmetry is introduced purely by fory's serialize/deserialize round trip.
+ */
+public class PackagePrivateCyclicSetChildLossTest {
+
+  private static final int CHILD_COUNT = 200;
+
+  @Test
+  public void testWideFanOutDoesNotLoseChildrenFromPackagePrivateSet() {
+    ThreadSafeFory fury =
+        Fory.builder()
+            .withXlang(false)
+            .requireClassRegistration(false)
+            .withRefTracking(true)
+            .withCompatible(false)
+            .buildThreadSafeFory();
+
+    FanOutContainer container = new FanOutContainer("v1");
+    FanOutNode parent = new FanOutNode(FanOutType.TYPE_A, "parent");
+    container.nodes.computeIfAbsent(FanOutType.TYPE_A, k -> new HashMap<>()).put(parent.id, parent);
+
+    List<String> expectedChildIds = new ArrayList<>();
+    for (int i = 0; i < CHILD_COUNT; i++) {
+      FanOutNode child = new FanOutNode(FanOutType.TYPE_B, "child-" + i);
+      parent.children.add(child);
+      child.parents.computeIfAbsent(parent.type, k -> new LinkedHashSet<>()).add(parent);
+      container.nodes.computeIfAbsent(FanOutType.TYPE_B, k -> new HashMap<>()).put(child.id, child);
+      expectedChildIds.add(child.id);
+    }
+
+    byte[] bytes = fury.serialize(container);
+    FanOutContainer result = (FanOutContainer) fury.deserialize(bytes);
+
+    FanOutNode resultParent = result.nodes.get(FanOutType.TYPE_A).get("parent");
+    assertEquals(resultParent.children.size(), CHILD_COUNT, "parent lost children from its Set field");
+
+    // Every child must still be reachable BOTH ways: down (parent.children) and up
+    // (child.parents), and both directions must point at the exact same object (fory's
+    // refTracking should unify identical (type,id) instances, not duplicate them).
+    List<String> asymmetric = new ArrayList<>();
+    for (String childId : expectedChildIds) {
+      FanOutNode resultChild = result.nodes.get(FanOutType.TYPE_B).get(childId);
+      boolean parentListsChild = resultParent.children.contains(resultChild);
+      boolean childListsParent =
+          resultChild.parents.getOrDefault(FanOutType.TYPE_A, Set.of()).contains(resultParent);
+      if (!parentListsChild || !childListsParent) {
+        asymmetric.add(
+            childId + " (parentListsChild=" + parentListsChild + ", childListsParent=" + childListsParent + ")");
+      }
+    }
+    assertTrue(
+        asymmetric.isEmpty(),
+        "asymmetric parent<->child edges after round trip (should be empty): " + asymmetric);
+  }
+}
+
+// All package-private — this triggers the bug
+enum FanOutType implements Serializable {
+  TYPE_A,
+  TYPE_B
+}
+
+class FanOutNode implements Serializable {
+  final FanOutType type;
+  final String id;
+  final Set<FanOutNode> children = new HashSet<>();
+  final Map<FanOutType, Set<FanOutNode>> parents = new EnumMap<>(FanOutType.class);
+
+  FanOutNode(FanOutType type, String id) {
+    this.type = type;
+    this.id = id;
+  }
+
+  @Override
+  public boolean equals(Object o) {
+    if (this == o) {
+      return true;
+    }
+    if (!(o instanceof FanOutNode)) {
+      return false;
+    }
+    FanOutNode other = (FanOutNode) o;
+    return type == other.type && id.equals(other.id);
+  }
+
+  @Override
+  public int hashCode() {
+    return Objects.hash(type, id);
+  }
+}
+
+class FanOutContainer implements Serializable {
+  final Map<FanOutType, Map<String, FanOutNode>> nodes = new EnumMap<>(FanOutType.class);
+  final String version;
+
+  FanOutContainer(String version) {
+    this.version = version;
+  }
+}