Add a WARN 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 +61,22 @@ public CompatibleFieldSerializer (Kryo kryo, Class type, CompatibleFieldSerializ
 		this.config = config;
 	}
 
+	@Override
+	protected void initializeCachedFields() {
+		if (!super.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();

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

@@ -24,17 +24,28 @@
 import com.esotericsoftware.kryo.Kryo;
 import com.esotericsoftware.kryo.KryoException;
 import com.esotericsoftware.kryo.KryoTestCase;
+import com.esotericsoftware.kryo.Serializer;
+import com.esotericsoftware.kryo.SerializerFactory;
 import com.esotericsoftware.kryo.SerializerFactory.CompatibleFieldSerializerFactory;
 
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
 import java.io.Serializable;
 import java.util.Arrays;
 import java.util.List;
 import java.util.Objects;
 
+import com.esotericsoftware.kryo.io.Input;
+import com.esotericsoftware.kryo.io.Output;
+import com.esotericsoftware.kryo.util.DefaultInstantiatorStrategy;
 import org.apache.commons.lang.builder.EqualsBuilder;
+import org.junit.Assert;
 import org.junit.Rule;
 import org.junit.Test;
 import org.junit.rules.ExpectedException;
+import org.objenesis.strategy.SerializingInstantiatorStrategy;
 
 /** @author Nathan Sweet */
 public class CompatibleFieldSerializerTest extends KryoTestCase {
@@ -642,4 +653,35 @@ public int hashCode () {
 			return Objects.hash(value, list, serializable);
 		}
 	}
+
+	@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);
+
+		ClassWithDuplicateField object2 = (ClassWithDuplicateField) kryo.readClassAndObject(input);
+		assertEquals(duplicateField, object2);
+	}
+
+	static class ClassWithDuplicateField extends SuperClassWithDuplicateField {
+		private Boolean customNote = true;
+	}
+
+	static class SuperClassWithDuplicateField implements Serializable {
+		private Boolean customNote = false;
+
+		public boolean equals(Object obj) {
+			if (this == obj) return true;
+			if (obj == null) return false;
+			if (getClass() != obj.getClass()) return false;
+			return true;
+		}
+	}
 }