pb: Fix bytes copy in oneOf

Author: Jozott00

protobuf/protobuf-core/src/commonTest/kotlin/kotlinx/rpc/protobuf/test/CopyTest.kt

@@ -4,11 +4,14 @@
 
 package kotlinx.rpc.protobuf.test
 
+import Equals
+import OneOfMsg
 import invoke
 import test.submsg.Other
 import test.submsg.invoke
 import kotlin.collections.iterator
 import kotlin.test.Test
+import kotlin.test.assertContentEquals
 import kotlin.test.assertEquals
 import kotlin.test.assertNull
 import kotlin.test.assertTrue
@@ -216,6 +219,19 @@ class CopyTest {
         assertEquals(listOf<Byte>(1, 2, 3), copy.bytes?.toList())
     }
 
+    @Test
+    fun `copy with bytes in oneof - mutating must not affect copy`() {
+        val userBytes = byteArrayOf(1, 2, 3)
+        val original = OneOfMsg {
+            field = OneOfMsg.Field.Bytes(userBytes)
+        }
+        val copy = original.copy()
+        userBytes[0] = 99
+
+        assertContentEquals(byteArrayOf(99, 2, 3), (original.field as OneOfMsg.Field.Bytes).value)
+        assertContentEquals(byteArrayOf(1, 2, 3), (copy.field as OneOfMsg.Field.Bytes).value)
+    }
+
     @Test
     fun `copy with empty collections`() {
         val msg = Repeated {

protobuf/protobuf-core/src/commonTest/proto/oneof.proto

@@ -8,6 +8,7 @@ message OneOfMsg {
     fixed64 fixed = 3;
     test.submsg.Other other = 4;
     kotlinx.rpc.protobuf.test.MyEnum enum = 5;
+    bytes bytes = 6;
   }
 }
 

protoc-gen/protobuf/src/main/kotlin/kotlinx/rpc/protoc/gen/ModelToProtobufKotlinCommonGenerator.kt

@@ -441,7 +441,9 @@ class ModelToProtobufKotlinCommonGenerator(
                 contextReceiver = oneOfFullName,
             ) {
                 // check if the type is copy by value (no need for deep copy)
-                val copyByValue = { type: FieldType -> type is FieldType.IntegralType || type is FieldType.Enum }
+                val copyByValue = { type: FieldType ->
+                    (type is FieldType.IntegralType && type != FieldType.IntegralType.BYTES) || type is FieldType.Enum
+                }
 
                 // if all variants are integral or enum types, we can just return this directly.
                 val fastPath = oneOf.variants.all { copyByValue(it.type) }