chore(metro-config)!: remove exotic transformer (#27855)

# Why

- We deprecated this feature in SDK 50 and now we'll drop all the source
related to it.
- We also pull out the cache key part for `babel-preset-fbjs` since this
is no longer used in metro.
- This PR no longer exports a getCacheKey from the babel transformer
since metro checks the file contents already.

---------

Co-authored-by: Expo Bot <34669131+expo-bot@users.noreply.github.com>

packages/@expo/metro-config/CHANGELOG.md

@@ -4,6 +4,8 @@
 
 ### 🛠 Breaking changes
 
+- Fully remove "exotic" transformer (`@expo/metro-config/transformer`) in favor of the default Expo transformer. ([#27855](https://github.com/expo/expo/pull/27855) by [@EvanBacon](https://github.com/EvanBacon))
+
 ### 🎉 New features
 
 - Add basic `react-server` support. ([#27264](https://github.com/expo/expo/pull/27264) by [@EvanBacon](https://github.com/EvanBacon))

packages/@expo/metro-config/README.md

@@ -1,6 +1,6 @@
 # `@expo/metro-config`
 
-This package contains the default Metro config that is required for bundling Expo apps.
+This package contains the default Metro config that is required for bundling apps with Expo CLI. Refer to the [Expo `metro.config.js` docs](https://docs.expo.dev/versions/latest/config/metro/) to learn more.
 
 `metro.config.js`
 
@@ -16,50 +16,8 @@ module.exports = config;
 
 ## Exotic
 
-Most of the [Exotic mode](https://blog.expo.dev/drastically-faster-bundling-in-react-native-a54f268e0ed1) performance benefits have been integrated in the default Expo CLI bundling pipeline (e.g. [less AST cloning](https://github.com/facebook/metro/pull/854), [faster worker creation](https://github.com/facebook/metro/pull/856)), and as such, the feature no longer needs to be enabled/disabled. Setting `mode: "exotic"` will no longer have any additional effects over the default.
-
-If you'd like to use different transformers (e.g. Sucrase) for different files, you can still create a custom transformer and refine it for your project needs.
-
-### Custom transformers
-
-> Caution: This is an advanced feature for developers who need to speed up the bundling of very large apps.
-
-You can use `@expo/metro-config/transformer` to create a custom multi-rule transformer. This is useful for running fewer transformations on node modules and speeding up bundling.
-
-`metro.transformer.js`
-
-```js
-const { createExoticTransformer } = require('@expo/metro-config/transformer');
-
-module.exports = createExoticTransformer({
-  transpileModules: ['@stripe/stripe-react-native'],
-  // You can uncomment the following lines to add any extra node_modules paths in a monorepo:
-  //   nodeModulesPaths: [
-  //     'node_modules',
-  //     // Generally you'll add this when your config is in `apps/my-app/metro.config.js`
-  //     '../../node_modules',
-  //     // If you have custom packages in a `packages/` folder
-  //     '../../packages',
-  //   ],
-});
-```
-
-Then use it in your project:
+> As of SDK 51, the exotic transformer has been fully removed in favor of the default `@expo/metro-config` transformer. The export `@expo/metro-config/transformer` no longer exists.
 
-`metro.config.js`
-
-```js
-const { getDefaultConfig } = require('@expo/metro-config');
-
-const config = getDefaultConfig(__dirname);
-
-// Use the new transformer
-config.transformer.babelTransformerPath = require.resolve('./metro.transformer');
-
-// Optionally, you can add support for the `react-native` resolver field back
-// doing this will increase bundling time and size as many community packages ship untransformed code using this feature.
-// Other packages like `nanoid` use the field to support `react-native` so you may need to enable it regardless.
-// defaultConfig.resolver.resolverMainFields.unshift('react-native');
+Most of the [Exotic mode](https://blog.expo.dev/drastically-faster-bundling-in-react-native-a54f268e0ed1) performance benefits have been integrated in the default Expo CLI bundling pipeline (e.g. [less AST cloning](https://github.com/facebook/metro/pull/854), [faster worker creation](https://github.com/facebook/metro/pull/856)), and as such, the feature no longer needs to be enabled/disabled. Setting `mode: "exotic"` will no longer have any additional effects over the default.
 
-module.exports = config;
-```
+Ensure you extend the `@expo/metro-config/babel-transformer` when customizing babel. Learn more: [Extending the Babel transformer](https://docs.expo.dev/versions/latest/config/metro/#extending-the-babel-transformer).