astral-sh/ruff · error · syn::Error

Unknown `cache_field` argument {name}

Error message

Unknown `cache_field` argument {name}

What it means

A syn compile error from parsing #[cache_field(...)] attributes in the CacheKey derive: an argument name other than the supported `ignore` was found. The attribute grammar only accepts ignore, so anything else is rejected at compile time.

Source

Thrown at crates/ruff_macros/src/cache_key.rs:143

#[derive(Debug, Default)]
struct CacheKeyFieldAttributes {
    ignore: bool,
}

impl Parse for CacheKeyFieldAttributes {
    fn parse(input: ParseStream) -> syn::Result<Self> {
        let mut attributes = CacheKeyFieldAttributes::default();

        let args = input.parse_terminated(Ident::parse, Token![,])?;

        for arg in args {
            match arg.to_string().as_str() {
                "ignore" => {
                    attributes.ignore = true;
                }
                name => {
                    return Err(Error::new(
                        arg.span(),
                        format!("Unknown `cache_field` argument {name}"),
                    ));
                }
            }
        }

        Ok(attributes)
    }
}

View on GitHub (pinned to 26f38c119c)

Solutions

1. Use only #[cache_field(ignore)] on fields
2. Remove the unsupported argument from the attribute

When it happens

Trigger: Thrown at crates/ruff_macros/src/cache_key.rs:143 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/e0b6f50e87852020. Report an issue: GitHub.