iterableToArray transitive usages not polyfilled

[RobHannay]

Bug Report

Current Behavior
When spreading a new Set with core-js 'usage', transitive dependencies are not polyfilled which breaks IE11.

We saw this live when it was not polyfilling 'Array.from', but on this repro it fails earlier because Symbol is also not polyfilled.

If Symbol is added manually it then fails saying it's not an iterable instance, but works fine on Chrome/FF.

Also if you use Array.from(new Set([])); it works fine.

Input Code
Access the Webpack dev server on Internet Explorer and see console errors.
https://babel-corejs-reproduce-set-spread.robhannay.repl.co

Code
https://repl.it/@robhannay/babel-corejs-reproduce-set-spread

Expected behavior/code
Expected the Symbol (or Array.from) 'usage' to be detected from within the iterableToArray method and itself be polyfilled

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

{
  presets: [
    ['@babel/preset-env', {
      modules: false, // Module transpilation is handled by Webpack
      corejs: 3,
      useBuiltIns: 'usage',
    }],
    '@babel/preset-react',
  ],
  plugins: [
    '@babel/plugin-transform-strict-mode',
    '@babel/plugin-proposal-object-rest-spread',
    '@babel/plugin-transform-object-assign',
    '@babel/plugin-syntax-dynamic-import',
    '@babel/plugin-transform-modules-commonjs',
    '@babel/plugin-transform-runtime',
    '@babel/plugin-proposal-class-properties',
  ],
}

Environment

• Babel version(s): v7.6.4
• Node/npm version: Node 12 / npm 6 (the repl.it runs on Node 10 but can see the same issue)
• OS: OSX local / Linux build producted same result
• Monorepo: no
• How you are using Babel: loader

Additional context/Screenshots

[babel-bot]

Hey @RobHannay! We really appreciate you taking the time to report an issue. The collaborators on this project attempt to help as many people as possible, but we're a limited number of volunteers, so it's possible this won't be addressed swiftly.

If you need any help, or just have general Babel or JavaScript questions, we have a vibrant Slack community that typically always has someone willing to help. You can sign-up here for an invite."

[nicolo-ribaudo]

If you aren't passing a file to Babel (you are excluding it in your webpack config with exclude: /node_modules/), Babel can't transform that code.

I usually suggest transforming the specific node_module with Babel, but since @babel/runtime is a Babel module itself it's really risky.

I suggest aliasing @babel/runtime to @babel/runtime-corejs3 in your webpack config.

[zloirock]

I suggest aliasing @babel/runtime to @babel/runtime-corejs3 in your webpack config.

For load both dependencies - core-js and core-js-pure? -) For proper work, in this case, required a version of runtime, compiled with injecting global core-js version.

[dcleao]

When you use @babel/plugin-transform-runtime without any options, the default for the corejs is false, which, per the docs means that the babel helpers with use the implementations provided by the @babel/runtime package.

The latter implementation of the babel runtime does not safe-guard any of its code, by importing core-js shims or by other means.

So, I'd say that this is not a bug, but by design.

If you want to include a version of the babel runtime which is safe for operation in certain browsers, you'll have to include one of the alternative provided builds: @babel/runtime-corejs2 or @babel/runtime-corejs3. You can do this by specifying the value 2 or 3 for the option corejs of the @babel/plugin-transform-runtime plugin...

Unfortunately, any of the mentioned builds end up depending and delegating on core-js-pure. If you have other code which is already using the non-pure core-js version, then you'll end up including the "same" core-js code twice (see vuejs/vue-cli#4742).

[nicolo-ribaudo]

Another option is to transpile @babel/runtime with @babel/preset-env.
We have been discouraging it for two reasons:

• @babel/plugin-transform-runtime can't be used to transpile @babel/runtime because it will inject circular dependencies. This can be solved by excluding that plugin for this package.
• @babel/preset-env could have some problems when transpiling the @babel/runtime/helpers/typeof helper with @babel/plugin-transform-typeof-symbol. At this point, your @babel/preset-env targets already exclude that polyfill, otherwise it needs to be explicitly excluded when transpiling this package.

Btw, I will look into how making it safer to transpile @babel/runtime.

[nicolo-ribaudo]

It's now safe to transpile `@babel/runtime}.