Fix CJS default interop with library bundler

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

@@ -578,4 +578,51 @@ describe('library bundler', function () {
  assert(!contents.includes('../'));
  }
  });
+
+ it('should support export default in CJS', async () => {
+ await fsFixture(overlayFS, dir)`
+ yarn.lock:
+
+ .parcelrc:
+ {
+ "extends": "@parcel/config-default",
+ "bundler": "@parcel/bundler-library"
+ }
+
+ package.json:
+ {
+ "module": "dist/module.js",
+ "main": "dist/main.js",
+ "engines": { "node": "*" }
+ }
+
+ index.js:
+ import foo from './foo';
+ export function test() {
+ return 'test:' + foo();
+ }
+
+ foo.js:
+ export default function foo() {
+ return 'foo';
+ }
+ `;
+
+ let b = await bundle(dir + '/index.js', {
+ inputFS: overlayFS,
+ mode: 'production',
+ });
+
+ let esm: any = await runBundle(
+ b,
+ nullthrows(b.getBundles().find(b => b.name === 'module.js')),
+ );
+ assert.equal(esm.test(), 'test:foo');
+
+ let cjs: any = await runBundle(
+ b,
+ nullthrows(b.getBundles().find(b => b.name === 'main.js')),
+ );
+ assert.equal(cjs.test(), 'test:foo');
+ });
 });

packages/packagers/js/src/ScopeHoistingPackager.js

@@ -828,8 +828,17 @@ ${code}
  if (imported === '*') {
  replacement = renamed;
  } else if (imported === 'default') {
- replacement = `($parcel$interopDefault(${renamed}))`;
- this.usedHelpers.add('$parcel$interopDefault');
+ let needsDefaultInterop = true;
+ if (referencedBundle) {
+ let entry = nullthrows(referencedBundle.getMainEntry());
+ needsDefaultInterop = this.needsDefaultInterop(entry);
+ }
+ if (needsDefaultInterop) {
+ replacement = `($parcel$interopDefault(${renamed}))`;
+ this.usedHelpers.add('$parcel$interopDefault');
+ } else {
+ replacement = `${renamed}.default`;
+ }
  } else {
  replacement = this.getPropertyAccess(renamed, imported);
  }