Summary:
This is a breaking change that tells Metro to look at only the project's .babelrc file. Previously it would look at .babelrc files under node_modules and would run into issues because it didn't have the version of Babel nor the plugins/presets that `node_modules/randompackage/.babelrc` wanted. So as a workaround, people would write a postinstall step that deletes `node_modules/**/.babelrc`, which worked well. This flag (`getEnableBabelRCLookup = false`) has the same effect and hopefully fixes one source of cryptic bugs people run into.
To use the old behavior, create a config file named `rn-cli.config.js` with:
```js
module.exports = {
getEnableBabelRCLookup() {
return true;
},
};
```
Go under node_modules, modify a used module to have a dummy .babelrc (`{"plugins": ["dummy"]}`) and ensure the JS bundle still loads.
Closes https://github.com/facebook/react-native/pull/15860
Differential Revision: D5798264
Pulled By: jeanlauliac
fbshipit-source-id: ce368b1d5671cc6c6261cbe3c39e61c9401fe37a
023ac57337