chore(metro-config): noop exotic mode (#24927)

# Why

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](facebook/metro#854), [faster worker
creation](facebook/metro#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.

# Checklist

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Please check the appropriate items below if they apply to your diff.
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- [ ] Documentation is up to date to reflect these changes (eg:
https://docs.expo.dev and README.md).
- [ ] Conforms with the [Documentation Writing Style
Guide](https://github.com/expo/expo/blob/main/guides/Expo%20Documentation%20Writing%20Style%20Guide.md)
- [ ] This diff will work correctly for `npx expo prebuild` & EAS Build
(eg: updated a module plugin).

---------

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

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

@@ -10,6 +10,8 @@
 
 ### 💡 Others
 
+- "Exotic mode", `EXPO_USE_EXOTIC`, and `EXPO_USE_FB_SOURCES` have been deprecated and no longer enable any experimental functionality. ([#24927](https://github.com/expo/expo/pull/24927) by [@EvanBacon](https://github.com/EvanBacon))
+
 ## 0.14.0 — 2023-10-17
 
 ### 🛠 Breaking changes

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

@@ -1,57 +1,32 @@
-<!-- Title -->
-<h1 align="center">
-👋 Welcome to <br><code>@expo/metro-config</code>
-</h1>
+# `@expo/metro-config`
 
-<p align="center">A Metro config for running React Native projects with the Metro bundler.</p>
+This package contains the default Metro config that is required for bundling Expo apps.
 
-<p align="center">
-  <img src="https://flat.badgen.net/packagephobia/install/@expo/metro-config">
-
-  <a href="https://www.npmjs.com/package/@expo/metro-config">
-    <img src="https://flat.badgen.net/npm/dw/@expo/metro-config" target="_blank" />
-  </a>
-</p>
-
-<!-- Body -->
+`metro.config.js`
 
-## Exotic
+```js
+// Learn more https://docs.expo.io/guides/customizing-metro
+const { getDefaultConfig } = require('expo/metro-config');
 
-When enabled, exotic mode adds the following assumptions:
+/** @type {import('expo/metro-config').MetroConfig} */
+const config = getDefaultConfig(__dirname);
 
-- Resolver Fields: `browser, main`
-  - The `react-native` field in module `package.json` is **NOT** supported.
-  - Packages using `react-native-builder-bob` will default to using the CommonJS setting in exotic. If you need to modify your Node modules manually, be sure to change the files in your `lib/commonjs/` folder.
-- Extensions: `ts, tsx, js, jsx, json, cjs`
-  - `cjs` is added.
-- `.babelrc` support is removed in favor of `babel.config.js`.
-- `x_facebook_sources` is toggled off by default.
+module.exports = config;
+```
 
-### Default Rules
+## Exotic
 
-1. Modules with `.*/lib/commonjs/` are skipped.
-2. React Native is transformed with Sucrase to remove flow types and other unsupported language features.
-   - If the React Native team transpiles react-native before shipping, we can remove this step.
-3. Expo modules are transformed with Sucrase to remove import/export syntax. This is temporary while we figure out how to add ESModule support to the native runtime.
-   - This is for improved tree shaking.
-4. Known community modules (especially ones included in Expo Go) are transformed using a more expensive Sucrase preset
-   - We may add support for extending this list in the future.
-5. All other node modules are skipped.
-6. All remaining code is assumed to be application code and transpiled with your local Babel preset.
-   - "Victory Native" packages use too many language features so they are transpiled with Babel.
+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.
 
-### Extra Customization
+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.
 
-> Experimental
+### Custom transformers
 
-You can use `@expo/metro-config/transformer` to extend the experimental transformer API.
-This can be used for:
+> Caution: This is an advanced feature for developers who need to speed up the bundling of very large apps.
 
-- Adding extra modules that need to be transpiled locally (`transpileModules`).
-- Adding extra `nodeModulesPaths` for monorepo support.
-- Adding support for the `react-native` main resolver field back.
+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-exotic-transformer.js`
+`metro.transformer.js`
 
 ```js
 const { createExoticTransformer } = require('@expo/metro-config/transformer');
@@ -76,15 +51,10 @@ Then use it in your project:
 ```js
 const { getDefaultConfig } = require('@expo/metro-config');
 
-const config = getDefaultConfig(__dirname, {
-  // Initialize in exotic mode.
-  // If you want to preserve `react-native` resolver main field, and omit cjs support, then leave this undefined
-  // and skip setting the `EXPO_USE_EXOTIC` environment variable.
-  mode: 'exotic',
-});
+const config = getDefaultConfig(__dirname);
 
 // Use the new transformer
-config.transformer.babelTransformerPath = require.resolve('./metro-exotic-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.
@@ -93,55 +63,3 @@ config.transformer.babelTransformerPath = require.resolve('./metro-exotic-transf
 
 module.exports = config;
 ```
-
-### Source Maps
-
-Metro bundler adds an undocumented extension to source maps which provides slightly different names for anonymous functions. The source map sizes increase a lot by adding the `x_facebook_sources` object, and the net transformation time also increases by a noticeable amount. By default, exotic disables this feature. The feature can be re-enabled with `EXPO_USE_FB_SOURCES`. Here are the results:
-
-<table>
-<tr>
-    <th>Enabled</th>
-    <th>Disabled</th>
-  </tr>
- <tr>
-    <td>iOS Bundling: <b>7664ms</b></td>
-    <td>iOS Bundling: <b>6875ms</b></td>
-  </tr>
- <tr>
-    <td><img src="https://user-images.githubusercontent.com/9664363/134078785-c9b0d93d-3dfb-4552-b786-b45059e10c3b.png" width="200" /></td>
-    <td><img src="https://user-images.githubusercontent.com/9664363/134078781-9f79e9d8-56c7-4e20-952f-8214deb3f0ca.png" width="200" /></td>
-  </tr>
-</table>
-
-- Most error reporting services don't support `x_facebook_sources` so the larger size mostly just increases hosting costs (when uploaded).
-- Documentation for `x_facebook_sources` is not provided.
-
-Cite: [#3861](https://github.com/expo/expo-cli/pull/3861)
-
-### Troubleshooting
-
-You should see the following log when Exotic is enabled:
-
-> Unstable feature **EXPO_USE_EXOTIC** is enabled. Bundling may not work as expected, and is subject to breaking changes.
-
-Or if `EXPO_DEBUG=1` is enabled, you'll see exotic mode in the settings breakdown.
-
-If you don't see this message, check to ensure your `metro.config.js` is using `@expo/metro-config` and the version is at least `0.2.2`.
-
-The transformer can be debugged using the environment variable: `DEBUG=expo:metro:exotic-babel-transformer` or `DEBUG=expo:metro:*`
-
-### Adding Resolver Fields
-
-You can add the `react-native` field back manually when exotic mode is enabled, we will investigate adding it back after more community packages have had time to adjust to transforming their code ahead of time.
-
-`metro.config.js`
-
-```js
-const { getDefaultConfig } = require('@expo/metro-config');
-
-const config = getDefaultConfig(__dirname);
-
-config.resolver.resolverMainFields.unshift('react-native');
-
-module.exports = config;
-```