BRP Issue: Components with only `Reflect` cannot be spawned/inserted

[natepiano]

Bevy version and features

• version: 0.16.1 but i believe the issue still persists
• no features

What you did

using the bevy remote protocol, if i try to bevy/spawn or bevy/insert on a Component and do not derive Deserialize and reflect Deserialize it gets an error

here's the report i came up with

BRP Issue: Components with only Reflect cannot be spawned/inserted

The Problem

In Bevy 0.16.1, components that only derive Reflect (without Serialize/Deserialize) fail to spawn via BRP with the error:

Unknown component type: `bevy_reflect::DynamicStruct`

Root Cause Analysis

When process_remote_spawn_request receives a spawn request:

1. deserialize_components creates a TypedReflectDeserializer and calls deserialize()

2. The deserializer checks for:

   • ReflectDeserialize (requires #[derive(Deserialize)] + #[reflect(Deserialize)])
   • ReflectDeserializeWithRegistry (requires manual registration)

3. Without these traits, it falls back to deserialize_struct() which creates a DynamicStruct - a generic container that knows it represents the actual type via set_represented_type()

4. This DynamicStruct is passed to insert_reflected_components which calls:

   get_reflect_component(type_registry, reflected.reflect_type_path())

5. The bug: reflect_type_path() on DynamicStruct returns "bevy_reflect::DynamicStruct" (from impl_type_path! macro) instead of the represented type's path

6. get_reflect_component fails because "bevy_reflect::DynamicStruct" isn't registered as a component

The Fix

In insert_reflected_components, check for a represented type first:

fn insert_reflected_components(
    type_registry: &TypeRegistry,
    mut entity_world_mut: EntityWorldMut,
    reflect_components: Vec<Box<dyn PartialReflect>>,
) -> AnyhowResult<()> {
    for reflected in reflect_components {
        let type_path = if let Some(represented_type_info) = reflected.get_represented_type_info() {
            represented_type_info.type_path()  // Use the actual component type
        } else {
            reflected.reflect_type_path()      // Fallback for non-dynamic types
        };
        
        let reflect_component = get_reflect_component(type_registry, type_path)?;
        reflect_component.insert(&mut entity_world_mut, &*reflected, type_registry);
    }

    Ok(())
}

Verification

I've tested this fix on Bevy 0.16.1 and confirmed it works - components with only Reflect can now be successfully spawned and inserted via BRP.

Help requested

I'm not a bevy contributor and i don't know the rules - mostly i'm concerned while that this is just a few lines of code to fix in an existing function i want to make sure that it's the right few lines of code. Not being a bevy_remote or bevy_reflect developer I would love it if someone who was could look at this issue and fix it correctly.

It's a big issue for me and I would love it if it this could make it into 17 as a bug fix.

[alice-i-cecile]

This seems very reasonable. I'll try and take a crack at a PR!

[alice-i-cecile]

Related to #20940.

[SkiFire13]

The deserializer checks for:

* `ReflectDeserialize` (requires `#[derive(Deserialize)]` + `#[reflect(Deserialize)]`)

* `ReflectDeserializeWithRegistry` (requires manual registration)

I wonder why it doesn't check for ReflectFromReflect though. That would probably also fix this issue.

[natepiano]

I wonder why it doesn't check for ReflectFromReflect though. That would probably also fix this issue.

i mean if that works, it'd be far better to do it up front i think then to check after the fact - it would keep insert_reflected_components simple and put the logic into deserialize where it already does the check on the other two early return paths.

I definitely endorse this

[alice-i-cecile]

I'd welcome a PR to that effect, with tests :) I think I'm convinced on the core idea. If it's done in time for 0.17 it'll ship, otherwise it should fit fine in a point release.