swc-project/swc · error

failed to parse #[ast_node]

Error message

failed to parse #[ast_node]

What it means

The #[ast_node] proc-macro attribute was applied to a token stream that syn could not parse as a DeriveInput. It fires when the attribute is placed on a non-item (function, module, statement) or on syntactically broken code, since #[ast_node] is only defined for struct/enum type definitions.

Source

Thrown at crates/ast_node/src/lib.rs:174

/// Structs derive `PartialEq` by default. Pass `no_partial_eq` after the node
/// tag when the type provides a manual implementation:
/// `#[ast_node("CustomNode", no_partial_eq)]`.
#[proc_macro_attribute]
pub fn ast_node(
    args: proc_macro::TokenStream,
    input: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
    let mut input: DeriveInput = parse(input).expect("failed to parse input as a DeriveInput");

    // we should use call_site
    let mut item = TokenStream::new();
    match &input.data {
        Data::Enum(data) => {
            use syn::parse::Parser;

            let attrs = <syn::punctuated::Punctuated<syn::Ident, syn::Token![,]>>::parse_terminated
                .parse(args)
                .expect("failed to parse #[ast_node]");

            let mut has_no_clone = false;
            let mut has_no_unknown = false;
            for attr in &attrs {
                if attr == "no_clone" {
                    has_no_clone = true;
                } else if attr == "no_unknown" {
                    has_no_unknown = true;
                } else {
                    panic!("unknown attribute: {attr:?}")
                }
            }

            let clone = if !has_no_clone {
                Some(quote!(#[derive(Clone)]))
            } else {
                None
            };

View on GitHub (pinned to 5176682b65)

Solutions

1. Attach #[ast_node("Tag")] only to struct or enum definitions
2. Ensure the annotated item is complete and syntactically valid before expansion
3. If another macro emits this item, confirm the emitted tokens form a valid DeriveInput

When it happens

Trigger: Thrown at crates/ast_node/src/lib.rs:174 when the library encounters an invalid state.

Common situations: See trigger scenarios.

Understand the failure class

• Parsing and encoding errors: unexpected token, malformed input — why parsers reject input and how to find the real culprit.

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/03a074bd033c0fdd. Report an issue: GitHub.