Private property transpilation broken w/ externalHelpers enabled

[nickschot]

ember-cli-babel currently has a pinned dependency of @babel/runtime 7.12.18. If a newer version (like 7.17.9) for whatever reason ends up on the root level of node_modules (like other dependencies bringing in a newer version) it may break the build at runtime in certain cases. The specific case that I ran into occurs when using private properties in native classes like in this reproduction: https://github.com/nickschot/babel-test-app/blob/master/app/controllers/application.js#L9

with externalHelpers: true configured in ember-cli-build.

When running the app this will result in a runtime error like:

The reproduction uses a private property in an app controller, but the same issue happens when addons use private properties in for example components.

Note that for the linked reproduction I've added a dependency on @babel/runtime 7.17.9 to force this issue. Disabling externalHelpers and/or making sure the version of @babel/runtime in the root of node_modules is 7.12.18 prevents the issue from occurring.

The pinning happened here: #385
May be somewhat related to: #420

[ef4]

We should consider includeExternalHelpers deprecated. Don't use it. You can avoid this bug and get a better build output by instead:

• add your own dependency directly on @babel/runtime
• add the @babel/plugin-transform-runtime directly to your own ember-cli-build.js

   const app = new EmberApp(defaults, {
     babel: {
      plugins: ['@babel/plugin-transform-runtime'],
    },
   });

The reason this is better is that ember-auto-import will take care of pulling the helpers into the build, and it will only pull in the ones you use. ember-cli-babel is doing a very naive and broken build of all the modules in @babel/runtime and forcing them into the app.

Keep in mind that some addon might be setting includeExternalHelpers and that also causes the problem. They're forcing you onto an old @babel/runtime, so they need to be fixed or worked around to stop it.