Issue a warning when final field is overwritten #414

src/main/java/net/openhft/chronicle/wire/WireMarshaller.java

@@ -450,6 +450,7 @@ abstract static class FieldAccess {
 
         Comment commentAnnotation;
         Boolean isLeaf;
+        boolean isFinalNoWarning;
 
         FieldAccess(@NotNull Field field) {
             this(field, null);
@@ -461,6 +462,10 @@ abstract static class FieldAccess {
             offset = unsafeObjectFieldOffset(field);
             key = field::getName;
             this.isLeaf = isLeaf;
+
+            if ((field.getModifiers() & Modifier.FINAL) != 0)
+                isFinalNoWarning = true;
+
             try {
                 commentAnnotation = field.getAnnotation(Comment.class);
             } catch (NullPointerException ignore) {
@@ -613,6 +618,8 @@ protected boolean sameValue(Object o, Object o2) throws IllegalAccessException {
         }
 
         protected void copy(Object from, Object to) throws IllegalAccessException {
+            triggerFinalWarning();
+
             ObjectUtils.requireNonNull(from);
             ObjectUtils.requireNonNull(to);
 
@@ -622,6 +629,8 @@ protected void copy(Object from, Object to) throws IllegalAccessException {
         protected abstract void getValue(Object o, ValueOut write, Object previous) throws IllegalAccessException;
 
         protected void readValue(Object o, Object defaults, ValueIn read, boolean overwrite) throws IllegalAccessException {
+            triggerFinalWarning();
+
             if (!read.isPresent()) {
                 if (overwrite && defaults != null)
                     copy(Objects.requireNonNull(defaults), o);
@@ -641,6 +650,14 @@ protected void readValue(Object o, Object defaults, ValueIn read, boolean overwr
             }
         }
 
+        protected void triggerFinalWarning() {
+            if (isFinalNoWarning) {
+                Jvm.warn().on(WireMarshaller.class, "Found final field " + field.getName() + " in " +
+                        field.getDeclaringClass() + ", final fields cannot be updated safely and will be ignored in future releases");
+                isFinalNoWarning = false;
+            }
+        }
+
         protected abstract void setValue(Object o, ValueIn read, boolean overwrite) throws IllegalAccessException;
 
         public abstract void getAsBytes(Object o, Bytes bytes) throws IllegalAccessException;
@@ -1093,6 +1110,8 @@ protected void getValue(final Object o, final ValueOut write, final Object previ
 
         @Override
         protected void readValue(Object o, Object defaults, ValueIn read, boolean overwrite) throws IllegalAccessException {
+            triggerFinalWarning();
+
             EnumSet coll = (EnumSet) field.get(o);
             if (coll == null) {
                 coll = enumSetSupplier.get();
@@ -1248,6 +1267,8 @@ protected void copy(Object from, Object to) throws IllegalAccessException {
 
         @Override
         protected void readValue(Object o, Object defaults, ValueIn read, boolean overwrite) throws IllegalAccessException {
+            triggerFinalWarning();
+
             Collection coll = (Collection) field.get(o);
             if (coll == null) {
                 coll = collectionSupplier.get();
@@ -1337,6 +1358,8 @@ protected void getValue(Object o, @NotNull ValueOut write, Object previous) thro
 
         @Override
         protected void readValue(Object o, Object defaults, ValueIn read, boolean overwrite) throws IllegalAccessException {
+            triggerFinalWarning();
+
             Collection coll = (Collection) field.get(o);
             if (coll == null) {
                 coll = collectionSupplier.get();
@@ -1417,6 +1440,8 @@ protected void copy(Object from, Object to) throws IllegalAccessException {
 
         @Override
         protected void readValue(Object o, Object defaults, ValueIn read, boolean overwrite) throws IllegalAccessException {
+            triggerFinalWarning();
+
             Map map = (Map) field.get(o);
             if (map == null) {
                 map = collectionSupplier.get();

src/test/java/net/openhft/chronicle/wire/FinalFieldsTest.java

@@ -0,0 +1,72 @@
+/*
+ * Copyright 2016-2020 chronicle.software
+ *
+ *  Licensed 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 net.openhft.chronicle.wire;
+
+import net.openhft.chronicle.bytes.Bytes;
+import org.junit.Test;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import static org.junit.Assert.assertEquals;
+
+public class FinalFieldsTest extends WireTestCommon {
+    @SuppressWarnings("rawtypes")
+    @Test
+    public void testCopy() {
+        expectException("Found final field map");
+        expectException("Found final field array");
+        expectException("Found final field intValue");
+        expectException("Found final field value");
+
+        Bytes bytesFrom = Bytes.allocateElasticOnHeap(64);
+        Wire wireFrom = WireType.BINARY.apply(bytesFrom);
+        Bytes bytesTo = Bytes.allocateElasticOnHeap(64);
+        Wire wireTo = WireType.JSON.apply(bytesTo);
+
+        FinalFieldsClass a = create();
+
+        wireFrom.getValueOut().marshallable(a);
+
+        wireFrom.copyTo(wireTo);
+        FinalFieldsClass b = wireTo.getValueIn().object(FinalFieldsClass.class);
+
+        assertEquals(a, b);
+    }
+
+    private FinalFieldsClass create() {
+        Map<CcyPair, String> map = new HashMap<>();
+        map.put(CcyPair.EURUSD, "eurusd");
+        return new FinalFieldsClass(map, new String[]{"hello", "there"}, 11, 123.4);
+    }
+
+    @SuppressWarnings("unused")
+    private static class FinalFieldsClass extends SelfDescribingMarshallable {
+        final Map<CcyPair, String> map;
+        final String[] array;
+        final int intValue;
+        final double value;
+
+        public FinalFieldsClass(Map<CcyPair, String> map, String[] array, int intValue, double value) {
+            this.map = map;
+            this.array = array;
+            this.intValue = intValue;
+            this.value = value;
+        }
+    }
+}