swc-project/swc · error

unable to access unknown nodes

Error message

unable to access unknown nodes

What it means

fast_dts constant-evaluates enum member initializers; inside Expr::Lit it matches Lit keeping Str and Num as ConstantValue and returning None for Null/BigInt/Bool/Regex/JSXText. Under the swc_ast_unknown cfg (set by `--cfg=swc_ast_unknown` in wasm plugin builds) Lit gains an Unknown(tag, payload) variant; this arm panics because an unknown literal kind cannot be evaluated for enum member auto-numbering and string templates.

Source

Thrown at crates/swc_typescript/src/fast_dts/enum.rs:97

            });
        }
    }

    fn evaluate(
        &self,
        expr: &Expr,
        enum_name: &Atom,
        prev_members: &FxHashMap<Wtf8Atom, ConstantValue>,
    ) -> Option<ConstantValue> {
        match expr {
            Expr::Lit(lit) => match lit {
                Lit::Str(string) => Some(ConstantValue::String(string.value.clone())),
                Lit::Num(number) => Some(ConstantValue::Number(number.clone())),
                Lit::Null(_) | Lit::BigInt(_) | Lit::Bool(_) | Lit::Regex(_) | Lit::JSXText(_) => {
                    None
                }
                #[cfg(swc_ast_unknown)]
                _ => panic!("unable to access unknown nodes"),
            },
            Expr::Tpl(template) => {
                let mut quasis = template.quasis.iter();
                let first = quasis.next()?.cooked.as_ref()?;
                let mut value = Wtf8Buf::from(first);

                for (expr, quasi) in template.exprs.iter().zip(quasis) {
                    self.evaluate(expr, enum_name, prev_members)?
                        .push_to(&mut value);
                    value.push_wtf8(quasi.cooked.as_ref()?);
                }

                Some(ConstantValue::String(Wtf8Atom::from(&*value)))
            }
            Expr::Paren(expr) => self.evaluate(&expr.expr, enum_name, prev_members),
            Expr::Bin(bin_expr) => self.evaluate_binary_expr(bin_expr, enum_name, prev_members),
            Expr::Unary(unary_expr) => {
                self.evaluate_unary_expr(unary_expr, enum_name, prev_members)

View on GitHub (pinned to 5176682b65)

Solutions

1. Rebuild the plugin with the swc_core version matching the host
2. Update swc_core to latest so the literal decodes as a known Lit variant
3. Skip fast_dts for enums (or files) containing Unknown literals
4. Resync versions rather than catching and ignoring the panic

Example fix

# before
# enum E { A = <new-literal-kind> }  // host emits Lit::Unknown to old plugin
# fast_dts evaluates initializer -> panic

# after
swc_core = "=aligned-with-host"  # rebuild plugin
# literal decodes as Str/Num/...; evaluator returns Some/None normally

#[cfg(swc_ast_unknown)]
fn program_contains_unknown_lit(m: &swc_ecma_ast::Module) -> bool {
    use swc_ecma_ast::*;
    m.body.iter().any(|i| matches!(i, ModuleItem::Stmt(Stmt::Decl(Decl::TsEnum(e)))
        if e.members.iter().any(|mem| matches!(&mem.init, Some(
            box Expr::Lit(Lit::Unknown(..)))))))
}

#[cfg(swc_ast_unknown)]
fn lit_is_unknown(l: &swc_ecma_ast::Lit) -> bool {
    matches!(l, swc_ecma_ast::Lit::Unknown(..))
}

let out = std::panic::catch_unwind(std::panic::AssertUnwindSafe(|| {
    run_fast_dts(&mut program)
}));
if out.is_err() {
    return Err("unknown literal in enum initializer; realign swc_core".into());
}

When it happens

Trigger: fast_dts processes a TS enum whose member initializer deserialized as an unknown literal kind — a plugin compiled with --cfg=swc_ast_unknown against a swc_core older than the host that serialized the AST (e.g. a new literal node kind added upstream).

Common situations: Version skew between @swc/core host and plugin swc_core; prebuilt plugin wasm artifacts not rebuilt on host upgrade; new Lit variants in swc_ecma_ast releases.

Related errors

• unable to access unknown nodes
• unable to access unknown nodes
• unable to access unknown nodes
• Duplicated element (${element.key})
• Duplicated element (${elements[j].key})

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/c043fee57fb59227. Report an issue: GitHub.