Pin babel-preset-react-app to a minor core-js version as per core-js readme

Created by: Mrman

Is your proposal related to a problem?

I've been trying to polyfill Promise.allSettled for Edge by using react-app-polyfill/stable but failing. My expectation was that it should work since react-app-polyfill@1.0.6 depends on core-js@3.6.4 and Promise.allSettled was moved into core-js/stable on v3.2.0.

I've dug a bit deeper to find that babel-preset-react-app has corejs set to major version 3 (https://github.com/facebook/create-react-app/blob/v3.4.1/packages/babel-preset-react-app/dependencies.js#L91)

Looking at the core-js readme I see this:

Warning! Recommended to specify used minor core-js version, like corejs: '3.6', instead of corejs: 3, since with corejs: 3 will not be injected modules which were added in minor core-js releases.

Locally I've set corejs in babel-preset-react-app to 3.2 (just a proof this is the issue) and I can see Promise.allSettled is now polyfilled correctly.

It's not clear to me why babel-preset-react-app does not follow the advice of core-js and pin to a minor version?

Describe the solution you'd like

Update babel-preset-react-app to pin to a minor version of corejs in it's configuration.

Describe alternatives you've considered

Eject and manage babel-preset-env myself but I'm very reluctant to go down this route.

I look forward to being told why things aren't as simple as changing babel-preset-react-app configuration :)