astral-sh/ruff · error · syn::Error

expected {attribute_name} attribute to be a string: `{meta_n

Error message

expected {attribute_name} attribute to be a string: `{meta_name} = "..."`

What it means

A syn compile error from get_string_literal: the value of a default/value_type/scope/example key parsed to an expression that is not a string literal (e.g. a number, bool, or function call). The macro grammar requires `key = "..."`.

Source

Thrown at crates/ruff_macros/src/config.rs:351

    while let syn::Expr::Group(e) = value {
        value = &e.expr;
    }

    if let syn::Expr::Lit(ExprLit {
        lit: Lit::Str(lit), ..
    }) = value
    {
        let suffix = lit.suffix();
        if !suffix.is_empty() {
            return Err(syn::Error::new(
                lit.span(),
                format!("unexpected suffix `{suffix}` on string literal"),
            ));
        }

        Ok(lit.clone())
    } else {
        Err(syn::Error::new(
            expr.span(),
            format!("expected {attribute_name} attribute to be a string: `{meta_name} = \"...\"`"),
        ))
    }
}

#[derive(Default, Debug)]
struct DeprecatedAttribute {
    since: Option<String>,
    note: Option<String>,
}

View on GitHub (pinned to 26f38c119c)

Solutions

1. Wrap the value in double quotes so it is a string literal
2. Use a plain string, not an expression, for the attribute value

When it happens

Trigger: Thrown at crates/ruff_macros/src/config.rs:351 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/bf47e8d155eccda6. Report an issue: GitHub.