Avoid non-identifier export names in non-entry library bundles (#9587)

packages/core/integration-tests/test/library-bundler.js

@@ -3,6 +3,7 @@ import assert from 'assert';
 import path from 'path';
 import {
   bundle,
+  run,
   runBundle,
   overlayFS,
   outputFS,
@@ -367,4 +368,54 @@ describe('library bundler', function () {
     assert.equal(cjs.foo(), 'foo');
     assert.equal(cjs.bar(), 2);
   });
+
+  it('should export CJS namespaces as default', async function () {
+    await fsFixture(overlayFS, dir)`
+      yarn.lock:
+
+      .parcelrc:
+        {
+          "extends": "@parcel/config-default",
+          "bundler": "@parcel/bundler-library"
+        }
+
+      package.json:
+        {
+          "module": "dist/module.js",
+          "engines": { "node": "*" }
+        }
+
+      index.js:
+        import ns from './foo.js';
+        export function test() {
+          return ns['foo-bar'];
+        }
+
+      foo.js:
+        exports['foo-bar'] = 'foo';
+    `;
+
+    let b = await bundle(path.join(dir, '/index.js'), {
+      inputFS: overlayFS,
+      mode: 'production',
+    });
+
+    assertBundles(b, [
+      {
+        assets: ['index.js'],
+      },
+      {
+        type: 'js',
+        assets: ['foo.js'],
+      },
+    ]);
+
+    let res = await run(b);
+    assert.equal(res.test(), 'foo');
+
+    // foo.js should only export default, to avoid non-identifier symbols.
+    let foo: any = await runBundle(b, b.getBundles()[1]);
+    assert.deepEqual(Object.keys(foo), ['default']);
+    assert.deepEqual(foo.default, {'foo-bar': 'foo'});
+  });
 });

packages/packagers/js/src/ScopeHoistingPackager.js

@@ -354,13 +354,22 @@ export class ScopeHoistingPackager {
     // TODO: handle ESM exports of wrapped entry assets...
     let entry = this.bundle.getMainEntry();
     if (entry && !this.wrappedAssets.has(entry.id)) {
+      let hasNamespace = entry.symbols.hasExportSymbol('*');
+
       for (let {
         asset,
         exportAs,
         symbol,
         exportSymbol,
       } of this.bundleGraph.getExportedSymbols(entry)) {
         if (typeof symbol === 'string') {
+          // If the module has a namespace (e.g. commonjs), and this is not an entry, only export the namespace
+          // as default, without individual exports. This mirrors the importing logic in addExternal, avoiding
+          // extra unused exports and potential for non-identifier export names.
+          if (hasNamespace && this.isAsyncBundle && exportAs !== '*') {
+            continue;
+          }
+
           let symbols = this.exportedSymbols.get(
             symbol === '*' ? nullthrows(entry.symbols.get('*')?.local) : symbol,
           )?.exportAs;