astral-sh/ruff · error · syn::Error

Mandatory `value_type` field is missing in `#[option]` attri

Error message

Mandatory `value_type` field is missing in `#[option]` attribute. Specify the value type using `#[option(value_type="..")]`.

What it means

Compile-time error emitted by the #[option] derive/attribute macro in ruff_macros while parsing a struct field's attributes. Every field marked #[option] must declare its value type so configuration documentation and schema generation can describe it; when parse_field_attributes (invoked via handle_option) finishes scanning the attribute's meta items without having collected a value_type entry, it reports this error pointing at the attribute span. The macro user fixes it by adding value_type=".." to the #[option(...)] attribute. Not a runtime error and not catchable — it aborts proc-macro expansion.

Source

Thrown at crates/ruff_macros/src/config.rs:281

                format!(
                    "Deprecated meta {:?} is not supported by ruff's option macro.",
                    meta.path.get_ident()
                ),
            ));
        }

        Ok(())
    })?;

    let Some(default) = default else {
        return Err(syn::Error::new(
            attribute.span(),
            "Mandatory `default` field is missing in `#[option]` attribute. Specify the default using `#[option(default=\"..\")]`.",
        ));
    };

    let Some(value_type) = value_type else {
        return Err(syn::Error::new(
            attribute.span(),
            "Mandatory `value_type` field is missing in `#[option]` attribute. Specify the value type using `#[option(value_type=\"..\")]`.",
        ));
    };

    let Some(example) = example else {
        return Err(syn::Error::new(
            attribute.span(),
            "Mandatory `example` field is missing in `#[option]` attribute. Add an example using `#[option(example=\"..\")]`.",
        ));
    };

    Ok(FieldAttributes {
        default,
        value_type,
        example,
        scope,
    })

View on GitHub (pinned to 26f38c119c)

Solutions

1. Add #[option(value_type = "...")] describing the option's type
2. Check for typos in the key name

When it happens

Trigger: Thrown at crates/ruff_macros/src/config.rs:281 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of astral-sh/ruff@26f38c119c (2026-09-05). Data as JSON: /api/errors/be36028d5d6bd360. Report an issue: GitHub.