Extract Babel configuration to a separate package

[fson]

Once the monorepo configuration in #419 has landed, we should move Babel configuration to a preset package and linting rules to an ESLint config package.

This will improve the ejected experience, because we will generate less configuration and also simplify some of the underlying code, which is getting quite complex because of the differences between running inside react-scripts and in the ejected mode (as can be seen in #602).

In the long term providing smaller configuration packages makes it easier to eject without opting in to maintain all the aspects of the config. This can also make forks that reuse the config easier to maintain.

[fson]

I could look into this soon, but I wonder what we should call these packages? I'll throw in some random ideas:

• Babel preset: babel-preset-react-app, babel-preset-react-recommended, babel-preset-create-react-app?
• ESLint config: probably similar to the Babel preset name, but prefixed eslint-config-?

[fson]

Renaming this issue to be only about the Babel preset, because there was a separate issue about ESLint config: #655.

[AlicanC]

I vote for babel-preset-create-react-app since CRA will be its scope.

(Though, in the future, I'd love to see official FB recommandations under babel-preset-facebook and eslint-config-facebook which CRA, React and React Native would use or compose.)

[fson]

@AlicanC There's already eslint-config-fbjs which is used at least in FBJS, and (with stricter extensions) in React and Jest.

However it seems to me that an CRA's configuration (used for React apps) would have different goals than than the FBJS configuration (used for FB libraries).

[gaearon]

babel-preset-react-app sounds good. Squatted.

[gaearon]

@fson Do you think you can take this?

[fson]

@gaearon Yeah, planning to tackle this today or tomorrow. Should be pretty straightforward now that presets can also accept options (we probably need this for different development/production configs).

[gaearon]

I think it might be reasonable to just use Babel env option and not use configuration.

[gaearon]

As a follow up we should make it so we have a .babelrc instead of two configs, and copy that file when ejecting.

[fson]

Absolutely. I had this is mind when doing the split already, but didn't want to touch too many things at once.