[preset-env] all the core-js imports are removed

Bug Report

Current behavior

No core-js polyfills in the final bundle.

Since https://github.com/babel/babel/pull/10862 the core-js polyfill paths always have .js extension. In shouldReplace function https://github.com/babel/babel/blob/41085248560b1403b8d0f99f108491e679531c6c/packages/babel-preset-env/src/polyfills/corejs3/entry-plugin.js#L52-L64 the module path is compared with the source. In my application the comparison happens between core-js/modules/es.symbol and core-js/modules/es.symbol.js causing the function to return different value than expected.

• Repo to reproduce the problem: https://github.com/ertrzyiks/babel-loader-lost-polyfills-demo

Input Code

import 'core-js'

console.log([1, [2]].flat())

Expected behavior Importing core-js includes polyfill to the final bundle

Babel Configuration (babel.config.js, .babelrc, package.json#babel, cli command, .eslintrc)

• Filename: babel.config.js

module.exports = {
  mode: 'production',
  module: {
    rules: [
      {
        test: /\.js$/,
        use: {
          loader: 'babel-loader',
          options: {
            cacheDirectory: false,
            presets: [
              ['@babel/preset-env', { corejs: 3, useBuiltIns: 'entry' }],
               'react-app'
            ]
          }
        }
      }
    ]
  }
};

Environment

npx envinfo --preset babel
npx: installed 1 in 1.147s

  System:
    OS: macOS 10.15.4
  Binaries:
    Node: 12.16.1 - ~/.nvm/versions/node/v12.16.1/bin/node
    Yarn: 1.22.4 - ~/.nvm/versions/node/v12.16.1/bin/yarn
    npm: 5.1.0 - ~/workspace/app/node_modules/.bin/npm
  npmPackages:
    @babel/core: ^7.0.0 => 7.12.10 
    @babel/preset-env: ^7.12.11 => 7.12.11 
    babel-loader: 8.2.2 => 8.2.2 
    babel-preset-react-app: ^10.0.0 => 10.0.0 
    webpack: ^4.44.2 => 4.44.2 

• How you are using Babel: webpack

Possible Solution Make the comparison ignore module path extension. My application compiles correctly if I alter the condition to exclude the extension. (note hardcoded string slice)

function shouldReplace(source, modules) {
    if (!modules) return false;

    if (modules.length === 1 && polyfills.has(modules[0]) && available.has(modules[0]) && (0, _utils.getModulePath)(modules[0]).slice(0, -3) === source) {
      return false;
    }

    return true;
  }

[nicolo-ribaudo]

We could use this to handle both the cases:

getModulePath(modules[0]) === source || getModulePath(modules[0]) === `${source}.js`

I’m marking this as a good first issue since it shouldn’t be too hard to fix it, but it gives the opportunity to setup the repo and learn how our tests work, and fixing it has a good impact since currently the whole useBuiltIns: "entry" feature is probably broken.

---

If it is the first time that you contribute to Babel, follow these steps: (you need to have make and yarn available on your machine)

1. Write a comment there to let other possible contributors know that you are working on this bug.
2. Fork the repo
3. Run git clone https://github.com/<YOUR_USERNAME>/babel.git && cd babel
4. Run make bootstrap to install deps and setup the monorepo
5. Wait ⏳
6. Run make watch (or make build whenever you change a file)
7. Add a test (only input.js/input.mjs; output.js will be automatically generated)
8. Update the code!
9. yarn jest preset-env to run the tests
   • If some test outputs don’t match but the new results are correct, you can delete the bad output.js files and run the tests again
   • If you prefer, you can run OVERWRITE=true yarn jest preset-env and they will be automatically updated.
10. If it is working, run make test to run all the tests
11. Run git push and open a PR!

[ertrzyiks]

Thanks @nicolo-ribaudo , I can work on a PR tomorrow morning