fix: Add support for parseUnknownFields in sub messages

pbj-core/pbj-compiler/src/main/java/com/hedera/pbj/compiler/impl/SingleField.java

@@ -216,7 +216,7 @@ public void addAllNeededImports(
     @Override
     public String parseCode() {
         if (type == FieldType.MESSAGE) {
-            return "%s.PROTOBUF.parse(input, strictMode, maxDepth - 1)".formatted(messageType);
+            return "%s.PROTOBUF.parse(input, strictMode, parseUnknownFields, maxDepth - 1)".formatted(messageType);
         } else {
             return "input";
         }

pbj-integration-tests/src/main/proto/bytes.proto

@@ -13,3 +13,13 @@ option java_multiple_files = true;
 message MessageWithBytes {
   bytes bytesField = 1;
 }
+
+/**
+ * Sample protobuf with MessageWithBytes as a oneof child message field.
+ */
+message MessageWithBytesWrapper {
+  oneof message_valid {
+    MessageWithBytes messageWithBytes = 1;
+    bool valid = 2;
+  }
+}

pbj-integration-tests/src/test/java/com/hedera/pbj/integration/test/UnknownFieldsTest.java

@@ -3,15 +3,18 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.hedera.pbj.integration.EverythingTestData;
+import com.hedera.pbj.runtime.OneOf;
 import com.hedera.pbj.runtime.ProtoConstants;
 import com.hedera.pbj.runtime.UnknownField;
 import com.hedera.pbj.runtime.io.buffer.BufferedData;
 import com.hedera.pbj.runtime.io.buffer.Bytes;
 import com.hedera.pbj.test.proto.pbj.Everything;
 import com.hedera.pbj.test.proto.pbj.MessageWithBytes;
 import com.hedera.pbj.test.proto.pbj.MessageWithBytesAndString;
+import com.hedera.pbj.test.proto.pbj.MessageWithBytesWrapper;
 import org.junit.jupiter.api.Test;
 import pbj.integration.tests.pbj.integration.tests.MessageWithEverythingUnknownFields;
 
@@ -95,4 +98,40 @@ void testEverythingRoundTrip() throws Exception {
         // and ensure it's equal to what we started with:
         assertEquals(EverythingTestData.EVERYTHING, everything);
     }
+
+    @Test
+    public void testUnknownFieldsInInnerMessage() throws Exception {
+        // write MessageWithBytesAndString
+        MessageWithBytesAndString messageWithBytesAndString = new MessageWithBytesAndString(TEST_BYTES, TEST_STRING);
+        final Bytes messageWithBytesAndStringBytes =
+                MessageWithBytesAndString.PROTOBUF.toBytes(messageWithBytesAndString);
+
+        // then read it as MessageWithBytes with unknown fields
+        final MessageWithBytes messageWithBytes = MessageWithBytes.PROTOBUF.parse(
+                messageWithBytesAndStringBytes.toReadableSequentialData(), false, true, 16);
+
+        final MessageWithBytesWrapper messageWithBytesWrapper = new MessageWithBytesWrapper(
+                new OneOf<>(MessageWithBytesWrapper.MessageValidOneOfType.MESSAGE_WITH_BYTES, messageWithBytes));
+        assertFalse(
+                messageWithBytesWrapper.messageWithBytes().getUnknownFields().isEmpty());
+        assertEquals(
+                1, messageWithBytesWrapper.messageWithBytes().getUnknownFields().size());
+
+        // write to bytes to simulate sending over the wire
+        final Bytes messageWithBytesWrapperBytes = MessageWithBytesWrapper.PROTOBUF.toBytes(messageWithBytesWrapper);
+
+        // parse bytes back as a receiving user would and confirm unknown fields exist in inner message
+        final MessageWithBytesWrapper parsedWrapper = MessageWithBytesWrapper.PROTOBUF.parse(
+                messageWithBytesWrapperBytes.toReadableSequentialData(), false, true, 16);
+        MessageWithBytes parsedBytes = parsedWrapper.messageWithBytes();
+        assertFalse(parsedBytes.getUnknownFields().isEmpty());
+        assertEquals(1, parsedBytes.getUnknownFields().size());
+
+        // now confirm that user can retrieve unknown fields when using expanded message MessageWithBytesAndString
+        final Bytes messageWithBytesBytes = MessageWithBytes.PROTOBUF.toBytes(parsedBytes);
+        final MessageWithBytesAndString messageWithBytesAndStringParsed =
+                MessageWithBytesAndString.PROTOBUF.parse(messageWithBytesBytes.toReadableSequentialData());
+        assertTrue(messageWithBytesAndStringParsed.getUnknownFields().isEmpty());
+        assertEquals(messageWithBytesAndString, messageWithBytesAndStringParsed);
+    }
 }