ReflectDeserializer does not error when deserializing incomplete enum value

[UkoeHB]

Bevy version

v0.13.0

What you did

#[derive(Reflect)]
enum E {
    A,
    B{ a: usize, b: usize },
}

1. Initialized an enum to E::A.
2. Created a reflected E::B with only one field by deserializing it from JSON using TypedReflectDeserializer.
3. Applied the incomplete reflected E::B to the enum with value E::A, using Reflect::apply.

What went wrong

This panic triggered. Basically, the reflect machinery cannot apply an incomplete enum variant to a different enum variant.

This is a bug because I expect the deserialize-from-JSON step to catch this kind of error so you never hit the panic. Note that, in contrast to enums, if you reflect-deserialize a struct with missing fields, then a serialization error will occur.

Additional information

You can avoid this panic by using FromReflect::from_reflect instead of Reflect::apply, which will fail without panicking.

If you don't want FromReflect::from_reflect to fail when a field is missing, use #[reflect(default)] on potentially-missing fields.

[mrchantey]

Not sure if its related but im also currently tracking down a bug for scene serde where enums are breaking in weird ways.

Code

#[derive(Reflect, Component)]
#[reflect(Component)]
enum Fizz {
  B(f32),  // this is ok
  A,
}

#[derive(Reflect, Component)]
#[reflect(Component)]
enum Bazz {
  A,       // this fails
  B(f32),
}

fn test() -> Result<()> {
  do_another_test(Bazz::B(0.5))?;
  do_another_test(Fizz::B(0.5))?;
  Ok(())
}


fn do_another_test<T: Reflect + GetTypeRegistration + Component>(val: T) -> Result<()> {
	let mut world = World::new();
	world.spawn(val);
	let registry = AppTypeRegistry::default();
	registry.write().register::<T>();
	world.insert_resource(registry.clone());
	let scene1 = DynamicScene::from_world(&world);

	let serialized1 =
		ron::ser::to_string(&SceneSerializer::new(&scene1, &registry))?;

	let mut deserializer = ron::de::Deserializer::from_str(&serialized1)?;
	let scene2 = SceneDeserializer {
		type_registry: &registry.read(),
	}
	.deserialize(&mut deserializer)?;

	let serialized2 =
		ron::ser::to_string(&SceneSerializer::new(&scene2, &registry))?;

	expect(serialized1).to_be(serialized2)?;
	Ok(())
}

output:

Expected: (resources:{},entities:{4294967296:(components:{\"my_crate::Bazz\":A(0.5)})})
Received: (resources:{},entities:{4294967296:(components:{\"my_crate::Bazz\":B(0.5)})})

[mrchantey]

@UkoeHB do you think these are related?

• issue DynamicScene - Malformed enum when reserializing #12462
• pr Fix: deserialize DynamicEnum using index #12464

[UkoeHB]

@mrchantey not sure if they are related, will need to test out the fix from #12464 to see. My problem doesn't seem to be deserialization, it's applying reflected enums to existing structs.