astral-sh/ruff · error · syn::Error

only named fields are supported

Error message

only named fields are supported

What it means

A syn compile error from the RuleNamespace derive: the input is not an enum (the destructuring expects Data::Enum with named-field variants). The derive builds prefix-to-linter mappings from enum variants, so structs/unions are rejected.

Source

Thrown at crates/ruff_macros/src/rule_namespace.rs:15

use std::cmp::Reverse;
use std::collections::HashSet;

use quote::quote;
use syn::spanned::Spanned;
use syn::{Attribute, Data, DataEnum, DeriveInput, Error, ExprLit, Lit, Meta, MetaNameValue};

pub(crate) fn derive_impl(input: DeriveInput) -> syn::Result<proc_macro2::TokenStream> {
    let DeriveInput {
        ident,
        data: Data::Enum(DataEnum { variants, .. }),
        ..
    } = input
    else {
        return Err(Error::new(
            input.ident.span(),
            "only named fields are supported",
        ));
    };

    let mut parsed = Vec::new();

    let mut common_prefix_match_arms = quote!();
    let mut name_match_arms =
        quote!(Self::Ruff => "Ruff-specific rules", Self::Numpy => "NumPy-specific rules", );
    let mut url_match_arms = quote!(Self::Ruff => None, Self::Numpy => None, );

    let mut all_prefixes = HashSet::new();

    for variant in variants {
        let mut first_chars = HashSet::new();
        let prefixes: Result<Vec<_>, _> = variant
            .attrs

View on GitHub (pinned to 26f38c119c)

Solutions

1. Apply the derive only to enums with named fields
2. Implement the namespace mapping manually for other shapes

When it happens

Trigger: Thrown at crates/ruff_macros/src/rule_namespace.rs:15 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/3d51b6330f3cc1fd. Report an issue: GitHub.