bevyengine/bevy · error · syn::Error

EntityEvent derive expected unnamed structs with one field o

Error message

EntityEvent derive expected unnamed structs with one field or with a field annotated with #[event_target].

What it means

Compile error from get_event_target_field: the struct is a tuple struct with multiple fields and none of them is annotated #[event_target], so the enumerated search over unnamed fields yielded no Member. The single-field fast path did not apply because unnamed.len() > 1.

Source

Thrown at crates/bevy_ecs/macros/src/event.rs:200

                } else {
                    None
                }
        }).ok_or(syn::Error::new(
            fields.span(),
            "EntityEvent derive expected a field name 'entity' or a field annotated with #[event_target]."
        )),
        Fields::Unnamed(fields) if fields.unnamed.len() == 1 => Ok(Member::Unnamed(Index::from(0))),
        Fields::Unnamed(fields) => fields.unnamed.iter().enumerate().find_map(|(index, field)| {
                if field
                    .attrs
                    .iter()
                    .any(|attr| attr.path().is_ident(EVENT_TARGET)) {
                        Some(Member::Unnamed(Index::from(index)))
                    } else {
                        None
                    }
            })
            .ok_or(syn::Error::new(
                fields.span(),
                "EntityEvent derive expected unnamed structs with one field or with a field annotated with #[event_target].",
            )),
        Fields::Unit => Err(syn::Error::new(
            fields.span(),
            "EntityEvent derive does not work on unit structs. Your type must have a field to store the `Entity` target, such as `Attack(Entity)` or `Attack { entity: Entity }`.",
        )),
    }
}

View on GitHub (pinned to 396ca72708)

When it happens

Trigger: Thrown at crates/bevy_ecs/macros/src/event.rs:200 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/8fdd806836b5214c. Report an issue: GitHub.