bevyengine/bevy · error · syn::Error

No variant found with the `#[from_world]` attribute

Error message

No variant found with the `#[from_world]` attribute

What it means

Compile error from derive_from_world when the input is an enum: the search over variants for one carrying the #[from_world] attribute found none, so no variant was selected for the generated FromWorld impl. The derive requires exactly one designated variant on enums.

Source

Thrown at crates/bevy_ecs/macros/src/lib.rs:902

#[proc_macro_derive(FromWorld, attributes(from_world))]
pub fn derive_from_world(input: TokenStream) -> TokenStream {
    let bevy_ecs_path = bevy_ecs_path();
    let ast = parse_macro_input!(input as DeriveInput);
    let name = ast.ident;
    let (impl_generics, ty_generics, where_clauses) = ast.generics.split_for_impl();

    let (fields, variant_ident) = match &ast.data {
        Data::Struct(data) => (&data.fields, None),
        Data::Enum(data) => {
            match data.variants.iter().find(|variant| {
                variant
                    .attrs
                    .iter()
                    .any(|attr| attr.path().is_ident("from_world"))
            }) {
                Some(variant) => (&variant.fields, Some(&variant.ident)),
                None => {
                    return syn::Error::new(
                        Span::call_site(),
                        "No variant found with the `#[from_world]` attribute",
                    )
                    .into_compile_error()
                    .into();
                }
            }
        }
        Data::Union(_) => {
            return syn::Error::new(
                Span::call_site(),
                "#[derive(FromWorld)]` does not support unions",
            )
            .into_compile_error()
            .into();
        }
    };

View on GitHub (pinned to 396ca72708)

Solutions

1. Mark exactly one enum variant with #[from_world]: #[from_world] Variant(Type,)
2. Use a struct instead, where the whole type gets the derived FromWorld impl
3. Ensure the attribute spelling matches `from_world` exactly

When it happens

Trigger: Thrown at crates/bevy_ecs/macros/src/lib.rs:902 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/4d4176d4c3d48504. Report an issue: GitHub.