Allow to disable __esModule

[TrySound]

Ref #708

This option will be useful for projects who distribute only cjs
and would like to migrate their codebase from default to named
exports but don't loose the ability to import in both ways.

For example react makes a hacky reexport right now

module.exports = React.default ? React.default : React;

Disabling __esModule will allow react to prepare their packages to esm.

[guybedford]

Just thinking through this here, if I made an entrypoint like:

react-entry.js

export { default } from './react.js';

Surely that would collapse down to the module.exports = React scenario, without an __esModule export? How does that not match the expected workflow in this case?

[TrySound]

The case is that I want to migrate react from default exports to named exports without breaking changes. So there won't be default export in react esm but it will be achievable in cjs. This will allow to do more work before achieving esm support.
https://github.com/facebook/react/blob/master/packages/react/src/React.js

[guybedford]

This sounds like a great effort, I'm just trying to understand why this isn't possible today. What if the entry above was written:

react-rollup-entry.js:

import * as React from './react.js';
export default React;

[guybedford]

Or is the issue that you want to be able to run the "cjs" and "esm" build on the same rollup input options?

[TrySound]

It's not achievable with reexport to default because of object.freeze which I can't disable because of react dependencies.

[guybedford]

@TrySound I see, then it definitely makes sense to have a little more control. I can get behind this.

[lukastaegert]

So between the lines I read that React will eventually be distributed as ESM as well? I remember a discussion that seemed to go nowhere at the end of last year. Great to hear you are moving forward here!

[TrySound]

Yes, we need to be very carefully here to not break existing stuff. The plan is continue supporting both import * as React from 'react' and import React from 'react' in react17 and upgrading community stuff (code, docs, tutorials). After that there will be a chance to get rid from default export.

[lukastaegert]

Will put this into an 0.61.0 release today, together with some other stuff.

[lukastaegert]

You might have left a solo:true in the tests. Will need to fix some things before I can release.

[TrySound]

Oops, sorry

[TrySound]

I will make a PR

[lukastaegert]

Nah, I already fixed everything