#847 Ensure that RecordSerializer can deal with subtypes

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

@@ -69,6 +69,8 @@ public class RecordSerializer<T> extends ImmutableSerializer<T> {
 		GET_TYPE = getType;
 	}
 
+	private boolean fixedFieldTypes = false;
+
 	public RecordSerializer () {
 	}
 
@@ -83,10 +85,14 @@ public void write (Kryo kryo, Output output, T object) {
 			final String name = rc.name();
 			try {
 				if (TRACE) trace("kryo", "Write property: " + name + " (" + type.getName() + ")");
-				if (rc.type().isPrimitive()) {
+				if (type.isPrimitive()) {
 					kryo.writeObject(output, componentValue(object, rc));
 				} else {
-					kryo.writeObjectOrNull(output, componentValue(object, rc), type);
+					if (fixedFieldTypes || kryo.isFinal(type)) {
+						kryo.writeObjectOrNull(output, componentValue(object, rc), type);
+					} else {
+						kryo.writeClassAndObject(output, componentValue(object, rc));
+					}
 				}
 			} catch (KryoException ex) {
 				ex.addTrace(name + " (" + type.getName() + ")");
@@ -109,11 +115,19 @@ public T read (Kryo kryo, Input input, Class<? extends T> type) {
 		for (int i = 0; i < recordComponents.length; i++) {
 			final RecordComponent rc = recordComponents[i];
 			final String name = rc.name();
+			final Class<?> rcType = rc.type();
 			try {
 				if (TRACE) trace("kryo", "Read property: " + name + " (" + type.getName() + ")");
 				// Populate values in the order required by the canonical constructor
-				values[rc.index()] = rc.type().isPrimitive() ? kryo.readObject(input, rc.type())
-					: kryo.readObjectOrNull(input, rc.type());
+				if (rcType.isPrimitive()) {
+					values[rc.index()] = kryo.readObject(input, rcType);
+				} else {
+					if (fixedFieldTypes || kryo.isFinal(rcType)) {
+						values[rc.index()] = kryo.readObjectOrNull(input, rcType);
+					} else {
+						values[rc.index()] = kryo.readClassAndObject(input);
+					}
+				}
 			} catch (KryoException ex) {
 				ex.addTrace(name + " (" + type.getName() + ")");
 				throw ex;
@@ -214,4 +228,10 @@ private static <T> T invokeCanonicalConstructor (Class<T> recordType,
 			throw ex;
 		}
 	}
+
+	/** Tells the RecordSerializer that all field types are effectively final. This allows the serializer to be more efficient,
+	 * since it knows field values will not be a subclass of their declared type. Default is false. */
+	public void setFixedFieldTypes (boolean fixedFieldTypes) {
+		this.fixedFieldTypes = fixedFieldTypes;
+	}
 }

test-jdk14/com/esotericsoftware/kryo/TestDataJava14.java

@@ -26,11 +26,11 @@
  * @author Chris Hegarty <chris.hegarty@oracle.com>
  */
 public class TestDataJava14 extends SerializationCompatTestData.TestData {
-    public record Rec (byte b, short s, int i, long l, float f, double d, boolean bool, char c, String str, Number[] n) { };
+    public record Rec (byte b, short s, int i, long l, float f, double d, boolean bool, char c, String str, Integer[] n) { };
 
     private Rec rec;
 
     public TestDataJava14() {
-        rec = new Rec("b".getBytes()[0], (short)1, 2, 3L, 4.0f, 5.0d, true, 'c', "foo", new Number[]{1,2,3});
+        rec = new Rec("b".getBytes()[0], (short)1, 2, 3L, 4.0f, 5.0d, true, 'c', "foo", new Integer[]{1,2,3});
     }
 }

test-jdk14/com/esotericsoftware/kryo/serializers/RecordSerializerTest.java

@@ -19,7 +19,7 @@
 
 package com.esotericsoftware.kryo.serializers;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.*;
 
 import com.esotericsoftware.kryo.KryoException;
 import com.esotericsoftware.kryo.KryoTestCase;
@@ -301,4 +301,21 @@ public void testRecordWithParametersReordered2() {
 
         roundTrip(6, r2);
     }
+
+    public static record RecordWithSuperType(Number n) {}
+
+    @Test
+    void testRecordWithSuperType() {
+        var rc = new RecordSerializer<RecordWithSuperType>();
+        kryo.register(RecordWithSuperType.class, rc);
+
+        final var r = new RecordWithSuperType(1L);
+        final var output = new Output(32);
+        kryo.writeObject(output, r);
+        final var input = new Input(output.getBuffer(), 0, output.position());
+        final var r2 = kryo.readObject(input, RecordWithSuperType.class);
+
+        roundTrip(3, r2);
+    }
+
 }