swc-project/swc · info

Unknown suffix `{}`

Error message

Unknown suffix `{}`

What it means

Internal helper of the `#[parallel]` macro: `node_type` maps the suffix of generated visit methods (`module_items`, `stmts`) to AST types (`ModuleItem`, `Stmt`). The macro's `expand` only ever calls it with those two literals, so `unimplemented!("Unknown suffix ...")` is unreachable from user code and acts as a completeness check for maintainers.

Source

Thrown at crates/swc_ecma_transforms_macros/src/parallel.rs:45

        .unwrap_or(false);

    item.items.push(ImplItem::Fn(make_par_visit_method(
        mode,
        "module_items",
        explode,
    )));
    item.items
        .push(ImplItem::Fn(make_par_visit_method(mode, "stmts", explode)));

    item
}

fn node_type(suffix: &str) -> Type {
    match suffix {
        "module_items" => parse_quote!(ModuleItem),
        "stmts" => parse_quote!(Stmt),
        _ => {
            unimplemented!("Unknown suffix `{}`", suffix)
        }
    }
}

fn post_visit_hook(mode: Mode, suffix: &str) -> Option<Expr> {
    match suffix {
        "module_items" => Some(match mode {
            Mode::Fold => parse_quote!(
                swc_ecma_transforms_base::perf::Parallel::after_module_items(self, &mut nodes)
            ),

            Mode::VisitMut => parse_quote!(
                swc_ecma_transforms_base::perf::Parallel::after_module_items(self, nodes)
            ),
        }),
        "stmts" => Some(match mode {
            Mode::Fold => parse_quote!(swc_ecma_transforms_base::perf::Parallel::after_stmts(
                self, &mut nodes

View on GitHub (pinned to d7d7434666)

Solutions

1. If extending the macro, add the new suffix mapping in `node_type` and the matching arm in `post_visit_hook`
2. No user-side action; if you see this panic on an unmodified swc, report it upstream

When it happens

Trigger: Not triggerable through normal macro usage; fires only if parallel.rs is modified to emit a method with a new suffix without extending `node_type`.

Common situations: Only swc contributors extending the #[parallel] macro itself.

Related errors

• Unknown visitor type: {:?}
• generic parameter other than type
• Box() -> T or Box without a type parameter
• Fast-path injection for Fold / VisitMut where pattern is not
• not implemented

AI-assisted analysis of swc-project/swc@d7d7434666 (2026-08-16). Data as JSON: /api/errors/767d916ad2b4af8f. Report an issue: GitHub.