commonjs: Object.defineProperty(exports, "__esModule", …) leaves unbound exports when module is wrapped

[trackoor]

In @rollup/plugin-commonjs 29.0.3 (with rollup 4.68.0), when a CommonJS module's only reference to exports is a top-level Object.defineProperty(exports, "__esModule", { value: true }) and the module also references module, it is wrapped in (function (module) { ... }()) without passing exports or rewriting the defineProperty call.

// m.js
"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
console.log(typeof module.exports);

// entry.js
require("./m.js");

// build.mjs
import { rollup } from "rollup";
import commonjs from "@rollup/plugin-commonjs";

const bundle = await rollup({ input: "entry.js", plugins: [commonjs()] });
const { output } = await bundle.generate({ format: "es" });
console.log(output[0].code);

Running the generated ES bundle throws ReferenceError: exports is not defined in ES module scope because requireM emits a free exports identifier inside the wrapper:

(function (module) {
	Object.defineProperty(exports, "__esModule", { value: true });
	console.log('object'); 
} ());

m.js should either receive (module, exports) in the wrapper or have exports rewritten, matching Node's CommonJS wrapper where both module and exports are in scope. The CallExpression handler for __esModule skips exports without marking uses.exports = true, so wrapping triggered by uses.module omits exports from the wrapper parameters.

Credit: https://ucsbplse.github.io/

[ItsRenjiii]

Confirmed with your repro on 29.0.3. The ES bundle throws ReferenceError: exports is not defined in ES module scope.

Your diagnosis is right. The top-level __esModule defineProperty call puts its exports argument in skippedNodes, so uses.exports is never set. When the module is wrapped because of the module reference, wrapCode only passes module, and the kept call is left referencing a free exports.

I've opened a PR with the fix: #2046. When a module is wrapped, it marks exports (or module, for the module.exports form) as used for those calls, so the wrapper becomes (function (module, exports) { ... } (m, m.exports)). With it, your repro prints object. The new test fails on master and passes with the change, and the plugin's 292 tests pass on Node 20 and 24.

Until that's released, adding any other plain use of exports to the module (e.g. exports.foo = ...) sets uses.exports, and the wrapper gets exports again.