bevyengine/bevy · error · syn::Error

reflection not supported for unions

Error message

reflection not supported for unions

What it means

Compile-time error raised in ReflectDeriveInput::from_input: #[derive(Reflect)] was applied to a union, which reflection does not support — only structs, enums, tuple structs, and unit structs can be reflected.

Source

Thrown at crates/bevy_reflect/derive/src/derive_data.rs:317

                let reflect_struct = ReflectStruct {
                    meta,
                    serialization_data,
                    fields,
                };

                match data.fields {
                    Fields::Named(..) => Ok(Self::Struct(reflect_struct)),
                    Fields::Unnamed(..) => Ok(Self::TupleStruct(reflect_struct)),
                    Fields::Unit => Ok(Self::UnitStruct(reflect_struct)),
                }
            }
            Data::Enum(data) => {
                let variants = Self::collect_enum_variants(&data.variants)?;

                let reflect_enum = ReflectEnum { meta, variants };
                Ok(Self::Enum(reflect_enum))
            }
            Data::Union(..) => Err(syn::Error::new(
                input.span(),
                "reflection not supported for unions",
            )),
        }
    }

    /// Set the remote type for this derived type.
    ///
    /// # Panics
    ///
    /// Panics when called on [`ReflectDerive::Opaque`].
    pub fn set_remote(&mut self, remote_ty: Option<RemoteType<'a>>) {
        match self {
            Self::Struct(data) | Self::TupleStruct(data) | Self::UnitStruct(data) => {
                data.meta.remote_ty = remote_ty;
            }
            Self::Enum(data) => {
                data.meta.remote_ty = remote_ty;

View on GitHub (pinned to 396ca72708)

Solutions

1. Replace the union with a struct or enum
2. Implement reflection manually for the union's wrapper type

When it happens

Trigger: Thrown at crates/bevy_reflect/derive/src/derive_data.rs:317 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of bevyengine/bevy@396ca72708 (2026-08-20). Data as JSON: /api/errors/05a818431f92f3fa. Report an issue: GitHub.