swc-project/swc · error

Type of node parameter should be reference but got {}

Error message

Type of node parameter should be reference but got {}

What it means

A compile-time macro validation panic in `expand` of swc_xml_codegen_macros (lib.rs:40). The #[emitter] macro requires its annotated method's second parameter (the node) to be a reference type; the macro strips the `&` and checks the remaining type. This panic fires when that parameter is not a `Type::Reference`, i.e. the user declared the emit_ method taking the node by value or with some other non-reference type. The offending parameter type in the macro input is the input at fault.

Source

Thrown at crates/swc_xml_codegen_macros/src/lib.rs:40

        format!("{}", i.sig.ident).starts_with("emit_"),
        "#[emitter] methods should start with `emit_`"
    );
    let block = {
        let node_type = {
            i.sig
                .inputs
                .clone()
                .into_iter()
                .nth(1)
                .and_then(|arg| match arg {
                    FnArg::Typed(ty) => Some(ty.ty),
                    _ => None,
                })
                .map(|ty| {
                    // &Ident -> Ident
                    match *ty {
                        Type::Reference(TypeReference { elem, .. }) => *elem,
                        _ => panic!(
                            "Type of node parameter should be reference but got {}",
                            ty.into_token_stream()
                        ),
                    }
                })
                .expect(
                    "#[emitter] methods should have signature of
fn (&mut self, node: Node) -> Result;
    ",
                )
        };

        let block = &i.block;
        parse_quote!({
            impl<W> crate::Emit<#node_type> for crate::CodeGenerator<'_, W>
                where W: crate::writer::XmlWriter,
            {
                fn emit(&mut self, n: &#node_type) -> crate::Result {

View on GitHub (pinned to 5176682b65)

Solutions

1. Change the #[emitter] method signature so the node parameter is a reference, e.g. `fn emit_ident(&mut self, node: &Ident)`
2. Add a clearer compile_error! that names the offending method and the expected signature
3. Document the required parameter shape near the #[emitter] macro definition

When it happens

Trigger: Thrown at crates/swc_xml_codegen_macros/src/lib.rs:40 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/3cda1a8ab93aef9c. Report an issue: GitHub.