entry points with an enum of exactly two variants fails

Rust-gpu rejects entry points with an enum of exactly two variants and no values. rustc seems to convert those to bools, and we have explicit checks to fail emitting bools. Maybe we should even reconsider whether we actually want to block bools this way, and handle them as two variant enums?

// build-pass
use spirv_std::spirv;
use spirv_std::glam::Vec4;

pub enum MyEnum {
    Variant1,
    Variant2,
}

#[spirv(fragment)]
pub fn main(
    #[spirv(storage_buffer, descriptor_set = 0, binding = 0)] value: &MyEnum,
    out: &mut Vec4,
) {
    *out = match value {
        MyEnum::Variant1 => Vec4::new(1., 0., 0., 1.),
        MyEnum::Variant2 => Vec4::new(0., 1., 1., 1.),
    }
}

fails with:

error: entry-point parameter cannot contain `bool`s
  --> $DIR/entry_point_enum_two_variants.rs:12:70
   |
12 |     #[spirv(storage_buffer, descriptor_set = 0, binding = 0)] value: &MyEnum,
   |                                                                      ^^^^^^^

error: aborting due to 1 previous error

Comienza con el caso build-pass entry_point_enum_two_variants.rs mostrado en el error y reproduce el rechazo de un enum de dos variantes pasado a un punto de entrada. Sigue la validación de los parámetros del punto de entrada que informa de que bools no son compatibles. Se considera terminado cuando se haya decidido el tratamiento previsto y este esté cubierto por una prueba de regresión que pase.