Add an exception for extendedFieldName

src/com/esotericsoftware/kryo/serializers/CompatibleFieldSerializer.java

@@ -32,6 +32,9 @@
 import com.esotericsoftware.kryo.util.ObjectMap;
 import com.esotericsoftware.kryo.util.Util;
 
+import java.lang.reflect.Field;
+import java.util.HashSet;
+
 /** Serializes objects using direct field assignment, providing both forward and backward compatibility. This means fields can be
  * added or removed without invalidating previously serialized bytes. Renaming or changing the type of a field is not supported.
  * Like {@link FieldSerializer}, it can serialize most classes without needing annotations.
@@ -58,6 +61,24 @@ public CompatibleFieldSerializer (Kryo kryo, Class type, CompatibleFieldSerializ
 		this.config = config;
 	}
 
+    @Override
+    protected void initializeCachedFields() {
+        if (config != null && !config.extendedFieldNames) {
+            final HashSet hashSet = new HashSet();
+            CachedField[] fields = cachedFields.fields;
+            for (int i = 0, n = fields.length; i < n; i++) {
+                final Field field = fields[i].field;
+                if (!hashSet.add(field.getName())) {
+                    if (WARN)
+                        warn("Detected duplicate field " + field.getName() + " in class hierarchy "
+                            + field.getDeclaringClass()
+                            + ". Consider enabling FieldSerializerConfig.extendedFieldNames");
+                    break;
+                }
+            }
+        }
+    }
+
 	@Override
 	public void write (Kryo kryo, Output output, T object) {
 		int pop = pushTypeVariables();
@@ -289,6 +310,12 @@ public boolean getChunkedEncoding () {
 			return chunked;
 		}
 
+        @Override
+        public void setExtendedFieldNames(boolean extendedFieldNames) {
+            this.extendedFieldNames = extendedFieldNames;
+            if (TRACE) trace("kryo", "CompatibleFieldSerializerConfig extendedFieldNames: " + extendedFieldNames);
+        }
+
 		/** The maximum size of each chunk for chunked encoding. Default is 1024. */
 		public void setChunkSize (int chunkSize) {
 			this.chunkSize = chunkSize;

test/com/esotericsoftware/kryo/WarnUnregisteredClassesTest.java

@@ -125,7 +125,7 @@ public void write (Kryo kryo, Object object) {
 		output.flush();
 	}
 
-	class LoggerStub extends Logger {
+	public static class LoggerStub extends Logger {
 		public List<Integer> levels = new ArrayList();
 		public List<String> messages = new ArrayList();
 

test/com/esotericsoftware/kryo/serializers/CompatibleFieldSerializerTest.java

@@ -33,7 +33,10 @@
 import java.util.List;
 import java.util.Objects;
 
+import com.esotericsoftware.kryo.WarnUnregisteredClassesTest;
+import com.esotericsoftware.minlog.Log;
 import org.apache.commons.lang.builder.EqualsBuilder;
+import org.junit.Before;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
@@ -44,6 +47,16 @@ public class CompatibleFieldSerializerTest extends KryoTestCase {
 		supportsCopy = true;
 	}
 
+    WarnUnregisteredClassesTest.LoggerStub log;
+
+    @Before
+    public void setUp() throws Exception {
+        log = new WarnUnregisteredClassesTest.LoggerStub();
+        Log.setLogger(log);
+        Log.INFO();
+        kryo = new Kryo();
+    }
+
 	@Rule public ExpectedException exceptionRule = ExpectedException.none();
 
 	@Test
@@ -684,6 +697,47 @@ public int hashCode () {
 		}
 	}
 
+    @Test
+    public void testLogWarningOnDuplicateFieldInClassHierarchy() {
+        kryo.setReferences(true);
+        CompatibleFieldSerializer serializer = new CompatibleFieldSerializer(kryo, ClassWithDuplicateField.class);
+        serializer.getCompatibleFieldSerializerConfig().setChunkedEncoding(true);
+        serializer.getCompatibleFieldSerializerConfig().setExtendedFieldNames(false);
+        serializer.updateFields();
+        kryo.register(ClassWithDuplicateField.class, serializer);
+
+        final ClassWithDuplicateField duplicateField = new ClassWithDuplicateField();
+        roundTrip(31, duplicateField);
+        assertEquals(1, log.messages.size());
+    }
+
+    static class ClassWithDuplicateField extends SuperClassWithDuplicateField {
+        private Boolean customNote = true;
+    }
+
+    static class SuperClassWithDuplicateField implements Serializable {
+        private Boolean customNote = false;
+
+        public SuperClassWithDuplicateField() {}
+
+        public SuperClassWithDuplicateField(Boolean customNote) {
+            this.customNote = customNote;
+        }
+
+        public boolean equals(Object obj) {
+            if (this == obj)
+                return true;
+            if (obj == null)
+                return false;
+            if (getClass() != obj.getClass())
+                return false;
+            SuperClassWithDuplicateField other = (SuperClassWithDuplicateField)obj;
+            if (customNote != other.customNote)
+                return false;
+            return true;
+        }
+    }
+
 	public static class ClassWithObjectField {
 		Object value;