swc-project/swc · error

swcify: {:?}

Error message

swcify: {:?}

What it means

Converting a Babel/ESTree class body back to SWC AST (swcify) handles only Method, PrivateMethod, Prop, and PrivateProp elements. A class static block (ClassBodyEl::StaticBlock, `static { ... }`) or any other variant falls into the catch-all and panics with `unimplemented!("swcify: ...")`.

Source

Thrown at crates/swc_estree_compat/src/swcify/class.rs:35

impl Swcify for ClassBody {
    type Output = Vec<ClassMember>;

    fn swcify(self, ctx: &Context) -> Self::Output {
        self.body.swcify(ctx)
    }
}

impl Swcify for ClassBodyEl {
    type Output = ClassMember;

    fn swcify(self, ctx: &Context) -> Self::Output {
        match self {
            ClassBodyEl::Method(v) => v.swcify(ctx),
            ClassBodyEl::PrivateMethod(v) => v.swcify(ctx).into(),
            ClassBodyEl::Prop(v) => v.swcify(ctx).into(),
            ClassBodyEl::PrivateProp(v) => v.swcify(ctx).into(),
            _ => {
                unimplemented!("swcify: {:?}", self)
            }
        }
    }
}

impl Swcify for swc_estree_ast::ClassMethod {
    type Output = swc_ecma_ast::ClassMember;

    fn swcify(self, ctx: &Context) -> Self::Output {
        match self.kind.unwrap_or(ClassMethodKind::Method) {
            ClassMethodKind::Get | ClassMethodKind::Set | ClassMethodKind::Method => {
                let SwcifiedFunctionParams { this_param, params } =
                    swcify_function_params(self.params, ctx);

                swc_ecma_ast::ClassMethod {
                    span: ctx.span(&self.base),
                    key: self.key.swcify(ctx),
                    function: Function {

View on GitHub (pinned to 5176682b65)

Solutions

1. Strip/transform static blocks out of the Babel AST before swcify (e.g. Babel plugin converting them into an IIFE-initialized static private field, or removing them when side-effect free)
2. Implement a local conversion that maps ClassBodyEl::StaticBlock to swc_ecma_ast::ClassMember::StaticBlock before calling swcify
3. Upgrade swc_estree_compat where the arm may exist

Example fix

// before (input parsed by Babel)
class C { static { init(C); } }

// after (lower the static block before swcify)
class C { static __init = (() => { init(C); })(); }

// JS: detect static blocks in the Babel AST before swcify
function hasStaticBlock(ast) {
  return JSON.stringify(ast).includes('"type":"StaticBlock"');
}

function isSupportedClassBodyEl(el) {
  return ['ClassMethod', 'ClassPrivateMethod', 'ClassProperty', 'ClassPrivateProperty']
    .includes(el.type);
}

When it happens

Trigger: Running swcify on a Babel-parsed class that contains a `static { ... }` initialization block (ES2022), which SWC's ClassMember has as StaticBlock but this conversion path never constructs.

Common situations: Pipelines that parse with Babel and emit via SWC (or run SWC passes on Babel AST) on modern JS containing class static blocks; interop layers between Babel and SWC tooling.

Related errors

• Babel doesn't support this right now.
• module string names unimplemented
• swcify: {:?}
• failed to swcify arguments
• illegal conversion: Cannot convert {:?} to ClassBodyEl

AI-assisted analysis of swc-project/swc@5176682b65 (2026-08-17). Data as JSON: /api/errors/368c7a671a835e2c. Report an issue: GitHub.