tree shaking used in async modules, not found module

[rambo-panda]

🐛 bug report

🎛 Configuration (.babelrc, package.json, cli command)

// cli command
{
  production: true,
  scopeHoist: true,
  hmr: false,
  minify: !true,
  cache: false,
  watch: false,
  detailedReport: true,
  target: "browser",
  sourceMaps: false
}

💻 Code Sample

// a.js
const c = () => import('./c.js')
console.log(c);

// b.js
const c = () => import('./c.js')
console.log(c);

// c.js
export default () => {
	console.log(111);
}

// main.js
const a = () => import("./a.js");
const b = () => import("./b.js");

console.log(a);
console.log(b);

😯 Current Behavior

// generated a.js
var $KX6I$var$c = function c() {
  return ($_$init(), $_$exports)([["c.a92336cc.js", "KQUl"], "KQUl"]);
};

// generated b.js
var $gffB$var$c = function c() {
  return ($_$init(), $_$exports)("KQUl");
};

When the js resource is loaded in the browser order main.js b.js, then throw NOT FOUND KQUI module error.

🤔 Expected Behavior

If you are loading modules asynchronously, you should also keep information about their assetsDeps.

💁 Possible Solution

https://github.com/parcel-bundler/parcel/blob/parcel-bundler%401.12.1/packages/core/parcel-bundler/src/scope-hoisting/concat.js#L201

🔦 Context

🌍 Your Environment

Software	Version(s)
Parcel	1.12.1
Node	10.15.2
npm/Yarn	5.4.1
Operating System	mac 10.14

[mischnic]

Happens for me with this:
parcel build index.html --experimental-scope-hoisting

<script src="./index.js"></script>

// index.js
import("./a.js").then(() => {});
import("./b.js").then(() => {});


// a.js
import("./c.js").then(v => console.log("a", v.default));


// b.js
import("./c.js").then(v => console.log("b", v.default));


// c.js
export default 123;

[mischnic]

I'd say this is once again caused by Parcel's deduplication of assets.
The bundle of a.js does have c.js listed as a childBundle, but b.js doesn't.

[rambo-panda]

I'd say this is once again caused by Parcel's deduplication of assets.
The bundle of a.js does have c.js listed as a childBundle, but b.js doesn't.

That's it!

parcel/packages/core/parcel-bundler/src/Bundler.js

Lines 647 to 656 in cbccd25

	if (asset.parentBundle && !bundle.isolated) {
	// If the asset is already in a bundle, it is shared. Move it to the lowest common ancestor.
	if (asset.parentBundle !== bundle) {
	let commonBundle = bundle.findCommonAncestor(asset.parentBundle);
	// If the common bundle's type matches the asset's, move the asset to the common bundle.
	// Otherwise, proceed with adding the asset to the new bundle below.
	if (asset.parentBundle.type === commonBundle.type) {
	this.moveAssetToBundle(asset, commonBundle);
	return;

[mischnic]

@devongovett This would require quite a deep change (removing the duplicate assets/bundles only at a later stage). Will this be easier with Parcel 2?

[mischnic]

Should be fixed with Parcel 2