Enum variant doesn't impl Scene when passed into bsn

[will-hart]

Bevy version and features

bevy = { version = "0.19.0-rc.2", default-features = false, features = ["2d", "ui", "bevy_feathers"] }

What you did

I'm trying to create a bsn-based UI function that marks components with an enum variant. The bsn documentation suggests this should be possible. However when passing in an enum variant to the ui function and including it in the bsn macro, I get a compiler error.

What went wrong

I'm trying to create a function that returns a bsn Scene for UI. If I pass in an enum value to the function, it has a compiler error

the trait bound `MyEnum: bevy::prelude::Scene` is not satisfied
the following other types implement trait `bevy::prelude::Scene`:
  ()
  (P0, P1)
  (P0, P1, P2)
  (P0, P1, P2, P3)
  (P0, P1, P2, P3, P4)
  (P0, P1, P2, P3, P4, P5)
  (P0, P1, P2, P3, P4, P5, P6)
  (P0, P1, P2, P3, P4, P5, P6, P7)
and 15 others

I can resolve this by

• Deriving FromTemplate on the enum and hard coding the enum variant in the ui() function. Maybe related to Enums not working in bsn! macro without explicit FromTemplate derive #24469)
• Wrap the enum in a new type that implements the required traits, e.g. instead of adding enum_val, add MyEnumWrapper(enum_val)

Additional information

Minimal example.

use bevy::{feathers::FeathersPlugins, prelude::*};

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_plugins(FeathersPlugins)
        .add_systems(Startup, scene_list.spawn())
        .run();
}

#[derive(Component, Clone, Default)]
enum MyEnum {
    #[default]
    A,
}

fn scene_list() -> impl SceneList {
    bsn_list![ui(MyEnum::A)]
}

fn ui(enum_val: MyEnum) -> impl Scene {
    bsn! {
        enum_val
    }
}

Working alternatives:

#[derive(Component, Clone, Default)]
struct MyEnumWrapper(pub MyEnum);

fn ui(enum_val: MyEnum) -> impl Scene {
    bsn! {
        MyEnumWrapper(enum_val)
    }
}

or

// requires explicit `FromTemplate` on `MyEnum`
fn ui(enum_val: MyEnum) -> impl Scene {
    bsn! {
        MyEnum::A
    }
}