Code splitting with default exports produces broken CJS output

[nullobject]

• Rollup Version: 1.3.0
• Operating System (or Browser): Mac OS Mojave
• Node Version: 10.14.0

How Do We Reproduce?

Code splitting any modules with default exports will produce broken CJS output, even for very simple modules. I noticed the issue when reading this blog post by @lukastaegert.

Say we have two files:

// foo.js
export default 'hello'

// main.js
export { default as foo } from './foo'

When these files are bundled with code splitting we get:

// foo.js
module.exports = 'hello'

// main.js
var foo = require('./foo.js')
exports.foo = foo.default

But foo.default is undefined!

The blog post I mentioned earlier has a REPL which illustrates this issue. Just look at the CJS output and you'll see the export statements in main.js are broken.

Expected Behavior

// main.js
var foo = require('./foo.js');
exports.foo = foo;

Actual Behavior

// main.js
var foo = require('./foo.js');
exports.foo = foo.default;

[lukastaegert]

Thanks for spotting this. Just some notes to myself or whoever fixes this (I hope to find time soon but cannot make promises about the next days):

• we could just add the normal interop (not nice)
• much better: we make sure the chunk has the correct exports mode and dynamically determine from there how to retrieve the default

[lukastaegert]

Fix at #2727

[nullobject]

Legend, thank you ❤️