bevyengine/bevy · error · syn::Error

The `key` attribute is not supported for structs with named

Error message

The `key` attribute is not supported for structs with named fields

What it means

Compile error from derive_settings_group: the input is a struct with named fields (where each field already defines its own sub-key) but an explicit `key = "..."` override attribute was also supplied. The key attribute only applies to tuple/unit structs, so this guard rejects the combination.

Source

Thrown at crates/bevy_ecs/macros/src/lib.rs:707

                    } else if meta.path.is_ident("file") {
                        let value = meta.value()?;
                        let s: syn::LitStr = value.parse()?;
                        override_file = Some(s.value());
                        Ok(())
                    } else {
                        Err(meta.error("unsupported attribute"))
                    }
                })
                .ok()
            });

        (override_group_name, override_key_name, override_file)
    };

    let key_name = match &input.data {
        Data::Struct(data) => match data.fields {
            Fields::Named(_) if override_key_name.is_some() => {
                return syn::Error::new(
                    Span::call_site(),
                    "The `key` attribute is not supported for structs with named fields",
                )
                .into_compile_error()
                .into();
            }
            Fields::Named(_) => None,
            Fields::Unnamed(_) | Fields::Unit => {
                override_key_name.or_else(|| Some(pascal_to_snake_case(&name.to_string())))
            }
        },
        Data::Enum(_) => override_key_name.or(Some(pascal_to_snake_case(&name.to_string()))),
        Data::Union(_) => {
            return syn::Error::new(
                Span::call_site(),
                "SettingsGroup cannot be derived for unions",
            )
            .into_compile_error()

View on GitHub (pinned to 396ca72708)

Solutions

1. Remove the #[key = "...")] attribute and let named fields supply their own keys
2. Convert the struct to a tuple or unit struct if a single key override is needed
3. Apply key overrides at the field/group level where supported

When it happens

Trigger: Thrown at crates/bevy_ecs/macros/src/lib.rs:707 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/189f83f216dfb139. Report an issue: GitHub.