neon-bindings/neon · error

Unknown class attribute

Error message

Unknown class attribute '{}'

What it means

This is a compile-time error from Neon's `#[neon]` macro when parsing the attribute list inside `export(class(...))`. The macro only recognizes `name` as a valid attribute inside the parentheses; any other identifier is rejected. It ensures typo'd or unsupported class options fail fast instead of being silently ignored.

Solutions

1. Replace the unknown attribute with `name`: `export(class(name = "ClassName"))`.
2. Check the Neon docs for the exact set of supported `class` attributes (only `name` is currently accepted).
3. If you intended to rename the module export binding rather than the class itself, move the `name = "..."` attribute outside the parentheses: `export(class, name = "binding")`.

Example fix

// before
#[neon]
export(class(rename = "MyClass"))
// after
#[neon]
export(class(name = "MyClass"))

// Only `name` is a valid attribute inside export(class(...)):
// verify every key you write in class(...) is exactly `name`:
// #[neon] export(class(name = "..."))
const VALID_CLASS_ATTRS: [&str; 1] = ["name"];
fn check_attr(attr: &str) -> Result<(), String> {
    if VALID_CLASS_ATTRS.contains(&attr) { Ok(()) } else { Err(format!("Unknown class attribute '{}'", attr)) }
}

When it happens

Trigger: Writing `#[neon] export(class(rename = "Foo"))` or any attribute key other than `name` inside the `class(...)` parentheses of the export attribute, e.g. `export(class(fname = "X"))`.

Common situations: Developers guessing at attribute names (e.g. `class_name`, `rename`, `jsName`) based on other macro systems, copying patterns from `export(fn)` attributes, or upgrading Neon versions where an attribute may have been renamed or removed.

Understand the failure class

Background: "Invalid value" and "allowed values are" config errors: what your library rejected and how to fix it — this error's family across 41 libraries.

Related errors

• Unknown attribute
• Expected an owned `Channel` instead of a context reference.
• Context is not available in async functions. Try a…
• Expected a context argument after `&self` when using…
• Unexpected second receiver argument.

AI-assisted analysis of neon-bindings/neon@38960e4381 (2026-09-13). Data as JSON: /api/errors/73e4561d09db86ba. Report an issue: GitHub.

Appendix: source

Thrown at crates/neon-macros/src/export/class/meta.rs:41

        let mut meta = Meta::default();

        // Check for parenthesized attributes: class(name = "...")
        if input.peek(syn::token::Paren) {
            let content;
            syn::parenthesized!(content in input);

            // Parse attributes inside parentheses
            while !content.is_empty() {
                let name_token: syn::Ident = content.parse()?;

                match name_token.to_string().as_str() {
                    "name" => {
                        content.parse::<syn::Token![=]>()?;
                        let name_value: syn::LitStr = content.parse()?;
                        meta.class_name = Some(name_value.value());
                    }
                    _ => {
                        return Err(syn::Error::new(
                            name_token.span(),
                            format!("Unknown class attribute '{}'", name_token),
                        ));
                    }
                }

                // Parse optional comma
                if content.parse::<syn::Token![,]>().is_err() {
                    break;
                }
            }
        }

        // Check if there are additional attributes after "class" or "class(...)"
        if input.parse::<syn::Token![,]>().is_ok() {
            // Parse additional attributes like name = "..."
            while !input.is_empty() {
                let name_token: syn::Ident = input.parse()?;

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