rolldown miscompiles a re-exported default import of a CJS/builtin module: emits require(...) without __toESM but reads .default. tsc compiles the same source correctly. npm i && npm run rolldown

README.md

rolldown miscompiles a re-exported CJS default import

This TypeScript works under tsc, but crashes when bundled by rolldown.

npm install
npm run tsc        # compile with tsc, then run  -> WORKS
npm run rolldown   # bundle with rolldown, then run -> TypeError: Cannot read properties of undefined (reading 'Agent')

Environment: rolldown@1.1.3 (latest), typescript@5.7.3, node 22.

build.mjs

import { rolldown } from "rolldown";

const bundle = await rolldown({ input: "./entry.ts", platform: "node" });
await bundle.write({ format: "cjs", dir: "./dist", entryFileNames: "out.cjs" });

entry.ts

// Consumer, like node-http-handler.js. Type-correct: node_https is typed as the
// https module, so node_https.Agent is a valid `new`-able constructor.
import { node_https } from "./node-https";

export function makeAgent(): import("node:https").Agent {
  return new node_https.Agent({ keepAlive: true });
}

node-https.ts

// Exact shape of @smithy/node-http-handler@4.8.2 dist-es/node-https.js:
// default-import a CJS builtin, then re-export it through this module.
import node_https from "node:https";
export { node_https };

package.json

{
  "name": "rolldown-cjs-default-reexport-interop-bug",
  "version": "1.0.0",
  "private": true,
  "description": "rolldown miscompiles a default-imported CJS builtin that is re-exported through an intermediate module. tsc compiles the same source correctly.",
  "scripts": {
    "typecheck": "tsc --project tsconfig.json",
    "tsc": "tsc --project tsconfig.emit.json && node verify.cjs ./dist-tsc/entry.js",
    "rolldown": "node build.mjs && node verify.cjs ./dist/out.cjs"
  },
  "devDependencies": {
    "@types/node": "22.12.0",
    "rolldown": "1.1.3",
    "typescript": "5.7.3"
  }
}

tsconfig.emit.json

{
  "comment": "Contrast only: what tsc WOULD emit for the same source, targeting CommonJS. It is CORRECT and runs fine. Proves the bug is the bundler's emit, not the source or tsc.",
  "compilerOptions": {
    "target": "ESNext",
    "module": "CommonJS",
    "moduleResolution": "node",
    "esModuleInterop": true,
    "strict": true,
    "skipLibCheck": true,
    "outDir": "dist-tsc",
    "noEmit": false,
    "types": ["node"]
  },
  "include": ["entry.ts", "node-https.ts"]
}

tsconfig.json

{
  "comment": "Type-check only (noEmit). The source is type-correct; the bug is in the bundler's emit.",
  "compilerOptions": {
    "target": "ESNext",
    "module": "ESNext",
    "moduleResolution": "bundler",
    "verbatimModuleSyntax": true,
    "allowSyntheticDefaultImports": true,
    "isolatedModules": true,
    "strict": true,
    "skipLibCheck": true,
    "noEmit": true,
    "types": ["node"]
  },
  "include": ["entry.ts", "node-https.ts"]
}

verify.cjs

// Loads a built bundle, calls makeAgent(), and reports whether it produced a
// real https.Agent (intended behavior) instead of crashing.
const https = require("node:https");

const modulePath = process.argv[2];
const agent = require(modulePath).makeAgent();

console.log(
  `ran ${modulePath} -> OK.`,
  `instanceof https.Agent: ${agent instanceof https.Agent},`,
  `keepAlive: ${agent.keepAlive}`
);