Babel preset: don't override dev based on omission of redundant withDevTools, infer from env() instead.

[robhogan]

Summary:
Currently the RN Babel preset has this surprising bit of behaviour:

module.exports = (options, babel) => {
  if (options.withDevTools == null) {
    const env = process.env.BABEL_ENV || process.env.NODE_ENV;
    if (!env || env === 'development') {
      return getPreset(null, {...options, dev: true}, babel);
    }
  }
  return getPreset(null, options, babel);
};

If the (undocumented, otherwise unused) withDevTools option is set (to anything), we will override any given value of dev to true if BABEL_ENV || NODE_ENV || 'development' === 'development'.

To put that another way, with NODE_ENV=development and BABEL_ENV unset, we would always produce a dev bundle even if { dev: false }

Expo sets withDevTools: false to stop this happening, and always set dev (so this diff means no observable change under Expo):

https://github.com/expo/expo/blob/4a46dbff7a5a77d9fe06d30a70d7fab38cfc7f9a/packages/babel-preset-expo/build/index.js#L235-L236

This odd-looking override was introduced in 2017 in bc22a4d / D5237158 as a way to gate babel/plugin-transform-react-jsx-source, before the preset accepted any other options - it was never intended to override dev. Now, we gate that same plugin under options.dev.

Inferring dev when unspecified

The one potentially load-bearing piece of this is that, when a consumer specifies neither withDevTools nor dev (or maybe no options at all), this code serves to infer it from process.env.BABEL_ENV || process.env.NODE_ENV, which is reasonable and actually closer to the way typical plugins/presets work, but a better mechanism is to use the env() API (which defaults to process.env.BABEL_ENV || process.env.NODE_ENV).

https://babeljs.io/docs/config-files#apienv

This change

• Removes the obsolete use of withDevToolss, and never overrides the explicitly-passed dev
• Where dev is not specified, falls back to the Babel environment.

Changelog:
[General][Fixed] Babel-preset: Don't override explicitly-passed dev config if obsolete withDevTools is missing

Differential Revision: D94660480

[meta-codesync]

@robhogan has exported this pull request. If you are a Meta employee, you can view the originating Diff in D94660480.

[meta-codesync]

This pull request has been merged in c5a38ab.