swc-project/swc · error

failed to parse input as an item

Error message

failed to parse input as an item

What it means

The #[node_impl] proc-macro in swc_ecma_codegen_macros requires its input to be an impl block; this fires when syn cannot parse the attached item as an ItemImpl — e.g. the attribute is applied to a non-impl item (fn, struct, mod) or the impl block is syntactically malformed, during codegen macro expansion.

Source

Thrown at crates/swc_ecma_codegen_macros/src/lib.rs:39

///             ParamOrTsParamProp::TsParamProp(n) => emit!(n),
///         }
///     }
/// }
/// ```
///
///
/// ## `emit!()`.
///
/// `emit!()` macro in `#[node_impl]` functions are special.
///
/// Those are replaced with `emit_with` and `adjust_span` methods, depending on
/// the context.
#[proc_macro_attribute]
pub fn node_impl(
    _attr: proc_macro::TokenStream,
    item: proc_macro::TokenStream,
) -> proc_macro::TokenStream {
    let item: ItemImpl = syn::parse(item).expect("failed to parse input as an item");

    let mut output = TokenStream::new();

    for i in item.items {
        match i {
            ImplItem::Fn(i) => {
                let item = expand_node_impl_method(&item.self_ty, i);

                output.extend(item.to_token_stream());
            }

            _ => {
                panic!("Unexpected item: {i:?}");
            }
        }
    }

    output.into()

View on GitHub (pinned to 5176682b65)

Solutions

1. Apply #[node_impl] only to `impl` blocks
2. Ensure the impl block is complete and syntactically valid
3. If another macro generates the impl, verify the generated tokens form a valid ItemImpl

When it happens

Trigger: Thrown at crates/swc_ecma_codegen_macros/src/lib.rs:39 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/d6f8a5ba9634b759. Report an issue: GitHub.