Bug Report

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Current behavior
A clear and concise description of the behavior.

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When I use @babel/preset-env with the useBuiltIns option, the core-js imports still output without the .js. This is usually fine, except when running in a node environment that supports built-in modules, e.g. with type: module in the package.json or outputting to a file with the .mjs extension.

This happens even if I use --out-file-extension .mjs.

--out-file-extension .cjs works, if you don't use modules: false, but then you're not outputting modules.

Input Code

test.js

const greeting = new Set(['Hello', 'world!']);
console.log(Array.from(greeting).join(' '));

npx babel test.js -d test/
node test/test.js

Output:

internal/process/esm_loader.js:74
    internalBinding('errors').triggerUncaughtException(
                              ^

Error [ERR_MODULE_NOT_FOUND]: Cannot find module '<repo>/node_modules/core-js/modules/esnext.set.add-all' imported from <repo>/test/test.js
Did you mean to import core-js/modules/esnext.set.add-all.js?
    at finalizeResolution (internal/modules/esm/resolve.js:275:11)
    at packageResolve (internal/modules/esm/resolve.js:668:12)
    at moduleResolve (internal/modules/esm/resolve.js:716:14)
    at Loader.defaultResolve [as _resolve] (internal/modules/esm/resolve.js:809:11)
    at Loader.resolve (internal/modules/esm/loader.js:85:40)
    at Loader.getModuleJob (internal/modules/esm/loader.js:229:28)
    at ModuleWrap.<anonymous> (internal/modules/esm/module_job.js:51:40)
    at link (internal/modules/esm/module_job.js:50:36) {
  code: 'ERR_MODULE_NOT_FOUND'
}

Expected behavior
A clear and concise description of what you expected to happen (or code).

No errors

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

• Filename: babel.config.js

const presets = [['@babel/preset-env', {
  targets: {node: true},
  modules: false,
  useBuiltIns: 'usage',
  corejs: {version: 3, proposals: true},
}]];

export default {presets};

Environment

System:
  OS: android
Binaries:
  Node: 14.8.0 - /data/data/com.termux/files/usr/bin/node
  npm: 6.14.7 - /data/data/com.termux/files/usr/bin/npm
npmPackages:
  @babel/cli: ^7.10.5 => 7.10.5
  @babel/core: ^7.11.4 => 7.11.4
  @babel/preset-env: ^7.11.0 => 7.11.0

Possible Solution

One possible solution would be to always output with the extension. This would create longer output, but it would be future-proof and wouldn't require the user to do anything.

The best solution would probably be to guess whether the extension is needed, based on whether the package.json has type: module, and have a configuration option like addExtension or addCorejsExtension to force it one way or the other.

The last option I can think of is to always output .cjs, or add a configuration like changeExtension. .mjs would output to a .mjs file AND add the corejs path extensions. .cjs would output to .cjs and wouldn't add the extensions. .js, the default, would output to .js and possibly guess or use the addCorejsExtension option. I notice there is a --out-file-extension option for @babel/cli: having this keep the corejs extensions when you use .mjs would be fine, too.

Additional context
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