Rollup dynamic imports + tree-shaking API issue

README.md

Rollup bundle-splitting + tree-shaking bug

Install

1. Click "Download zip" and extract to a folder
2. cd into the extracted folder
3. npm install
4. npm start

The custom plugin in rollup.config.js will show an undefined value in the bundle argument passed to the generateBundle hook.

a.js

export default false
	? import('./b.js')
	: null;

b.js

export default "b";

output.md

Output

Actual

./a.js → ./dist...
{ entry: 'a.js', dynamicImports: [ undefined ] }
created ./dist in 21ms

Expected

./a.js → ./dist...
{ entry: 'a.js', dynamicImports: [ ] }
created ./dist in 20ms

Diff

./a.js → ./dist...
-{ entry: 'a.js', dynamicImports: [ ] }
+{ entry: 'a.js', dynamicImports: [ undefined ] }
created ./dist in 21ms

package.json

{
  "name": "rollup-code-splitting-treeshaking-bug",
  "version": "1.0.0",
  "description": "Repro for a rollup bug",
  "scripts": {
    "start": "rollup --config"
  },
  "license": "MIT",
  "devDependencies": {
    "rollup": "^1.1.0"
  }
}

rollup.config.js

module.exports = {
    input : [
        "./a.js",
    ],

    output : {
        dir : "./dist",
        format : "esm",
    },

    plugins : [
        {
            name : "rollup-code-splitting-treeshaking-bug",

            generateBundle(options, bundle) {
                Object.entries(bundle).forEach(([ entry, { dynamicImports }]) => {
                    console.log({ entry, dynamicImports });
                });
            },
        },
    ],
};