swc-project/swc · error

module string names unimplemented

Error message

module string names unimplemented

What it means

swc_bundler's module sorter scans statements to collect referenced Ids for dependency ordering (modules/sort/stmt.rs:574). Its visit_export_named_specifier only accepts identifier origs; `export { "a" as b }` (ModuleExportName::Str) hits unimplemented!() because there is no Id to insert into the ordering set. Bundling aborts with a panic (exit 101).

Source

Thrown at crates/swc_bundler/src/modules/sort/stmt.rs:574

}

impl Visit for RequirementCalculator {
    noop_visit_type!();

    weak!(visit_arrow_expr, ArrowExpr);

    weak!(visit_function, Function);

    weak!(visit_class_method, ClassMethod);

    weak!(visit_private_method, PrivateMethod);

    weak!(visit_method_prop, MethodProp);

    fn visit_export_named_specifier(&mut self, n: &ExportNamedSpecifier) {
        let orig = match &n.orig {
            ModuleExportName::Ident(ident) => ident,
            ModuleExportName::Str(..) => unimplemented!("module string names unimplemented"),
            #[cfg(swc_ast_unknown)]
            _ => panic!("unable to access unknown nodes"),
        };
        self.insert(orig.clone().into());
    }

    fn visit_assign_expr(&mut self, e: &AssignExpr) {
        let old = self.in_assign_lhs;

        self.in_assign_lhs = true;
        e.left.visit_with(self);

        self.in_assign_lhs = false;
        e.right.visit_with(self);

        self.in_assign_lhs = old;
    }

View on GitHub (pinned to d7d7434666)

Solutions

1. Normalize the export to identifier form in source.
2. Shim or patch dependencies that use string origs.
3. Add a pre-bundle SWC visitor converting ModuleExportName::Str to Ident.
4. Externalize the module until upstream support lands.

Example fix

// before
export { "a" as b };

// after
export { a as b };

// Module-sort pass scans all statements: screen before bundle()
use swc_ecma_visit::{Visit, VisitWith};
struct SortSafe { ok: bool }
impl Visit for SortSafe {
    fn visit_module_export_name(&mut self, n: &swc_ecma_ast::ModuleExportName) {
        if matches!(n, swc_ecma_ast::ModuleExportName::Str(_)) { self.ok = false; }
        n.visit_children_with(self);
    }
}
let mut v = SortSafe { ok: true };
m.visit_with(&mut v);
anyhow::ensure!(v.ok, "module sorter will panic on string export names");

fn sort_safe(m: &swc_ecma_ast::Module) -> bool {
    use swc_ecma_visit::{Visit, VisitWith};
    struct F(bool); impl Visit for F {
        fn visit_module_export_name(&mut self, n: &swc_ecma_ast::ModuleExportName) {
            if matches!(n, swc_ecma_ast::ModuleExportName::Str(_)) { self.0 = false; }
            n.visit_children_with(self);
        }
    }
    let mut f = F(true); m.visit_with(&mut f); f.0
}

let r = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| bundler.bundle(part)?));
match r {
    Ok(v) => v,
    Err(p) if format!("{:?}", &p).contains("module string names") =>
        Err(anyhow::anyhow!("string export name broke module sorting; normalize to identifiers")),
    Err(p) => std::panic::resume_unwind(p),
}

When it happens

Trigger: Any module in the graph declares a named export whose orig is a string literal; during statement scanning for topological sort, the Str arm panics.

Common situations: Same family as the other module-string-name panics: ES2022 arbitrary module namespace names in sources or dependencies; shows up during bundler's ordering pass; tools built on swc_bundler (spack-style pipelines) fail with this message.

Related errors

• module string names unimplemented
• module string names unimplemented
• module string names unimplemented
• module string names unimplemented
• module string names unimplemented

AI-assisted analysis of swc-project/swc@d7d7434666 (2026-08-16). Data as JSON: /api/errors/e6af48f9fd391e9c. Report an issue: GitHub.