swc-project/swc · error

Invalid type: {:?}

Error message

Invalid type: {:?}

What it means

In SWC's quote! macro, interpolated variables are typed by annotation, and only Ident, Expr, Pat, Str, and AssignTarget are accepted single-segment type names. A simple type path with any other name (e.g. `as Stmt`, `as Module`) panics the proc macro at compile time with 'Invalid type: {:?}'.

Source

Thrown at crates/swc_ecma_quote_macros/src/ctxt.rs:110

        let ident_str = ident.to_string();

        let pos = match var.ty {
            Some(syn::Type::Path(syn::TypePath {
                qself: None,
                path:
                    syn::Path {
                        leading_colon: None,
                        segments,
                    },
            })) => {
                let segment = segments.first().unwrap();
                match segment.ident.to_string().as_str() {
                    "Ident" => VarPos::Ident,
                    "Expr" => VarPos::Expr,
                    "Pat" => VarPos::Pat,
                    "Str" => VarPos::Str,
                    "AssignTarget" => VarPos::AssignTarget,
                    _ => panic!("Invalid type: {:?}", segment.ident),
                }
            }
            None => VarPos::Ident,
            _ => {
                panic!(
                    "Var type should be one of: Ident, Expr, Pat; got {:?}",
                    var.ty
                )
            }
        };

        let var_ident = syn::Ident::new(&format!("quote_var_{ident}"), ident.span());

        let old = init_map.entry(pos).or_default().insert(
            ident_str.clone(),
            VarData {
                pos,
                is_counting: true,

View on GitHub (pinned to 5176682b65)

Solutions

1. Change the annotation to one of Ident, Expr, Pat, Str, AssignTarget
2. For non-expression nodes (statements, declarations), restructure the macro to build them from expressions or use the builder API instead of interpolation
3. Check the macro docs/tests for the supported list before adding new interpolations

Example fix

// before
quote!(stmt_var as Stmt; console.log(stmt_var););

// after
quote!(expr_var as Expr; console.log(expr_var););

When it happens

Trigger: Writing quote! { x as Stmt; ... } or any interpolation annotated with a bare type name outside the five supported ones while authoring macros that use swc_ecma_quote_macros.

Common situations: Contributing to SWC or writing custom codegen with the quote macro, assuming any AST node type name can annotate an interpolation, porting examples that used older macro versions.

Related errors

• Var type should be one of: Ident, Expr, Pat; got {:?}
• Duplicate variable name: {ident_str}
• An element descriptor's .kind property must be either "metho
• An element descriptor's .placement property must be one of "
• A class descriptor's .kind property must be "class", but a d

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/5e2bc8514732fdea. Report an issue: GitHub.