feat(babel-preset-expo, expo-router): Add Expo Router babel features …

…to babel-preset-expo (#24779)

# Why

- Reduce the boilerplate required for expo-router by moving the babel
plugin features to babel-preset-expo.
- Make the expo-constants Metro web support work without Expo Router.
- Keeping expo-router/babel around for now since it shouldn't cause any
harm, this will support if someone needs to use Expo Router v3 with Expo
SDK 49 in the future (which probably won't work anyways).
- Fix #23819

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# How

- Move code from expo-router/babel.js to babel-preset-expo.
- Rewrite plugin to use TypeScript.
- Add tests.

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How did you build this feature or fix this bug and why?
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# Test Plan

- Added tests for the new plugins.

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reproduce your test, especially if this PR does not include automated
tests! If possible, please also provide terminal output and/or
screenshots demonstrating your test/reproduction.
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# Checklist

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Please check the appropriate items below if they apply to your diff.
This is required for changes to Expo modules.
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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

@@ -8,6 +8,7 @@
 
 ### 🎉 New features
 
+- Pass `projectRoot` to the Babel caller. ([#24779](https://github.com/expo/expo/pull/24779) by [@EvanBacon](https://github.com/EvanBacon))
 - Automatically optimize transformations based on Hermes usage. ([#24672](https://github.com/expo/expo/pull/24672) by [@EvanBacon](https://github.com/EvanBacon))
 
 ### 🐛 Bug fixes

packages/@expo/metro-config/src/__tests__/babel-transformer.test.ts

@@ -78,6 +78,7 @@ it(`passes the environment as isServer to the babel preset`, () => {
         bundler: 'metro',
         name: 'metro',
         platform: 'ios',
+        projectRoot: expect.any(String),
       },
       cloneInputAst: false,
       code: false,

packages/@expo/metro-config/src/babel-transformer.ts

@@ -222,6 +222,9 @@ const transform: BabelTransformer['transform'] = ({
         // Pass the engine to babel so we can automatically transpile for the correct
         // target environment.
         engine: options.customTransformOptions?.engine,
+
+        // Provide the project root for accurately reading the Expo config.
+        projectRoot: options.projectRoot,
       },
       ast: true,
 

packages/babel-preset-expo/CHANGELOG.md

@@ -7,6 +7,7 @@
 ### 🎉 New features
 
 - Automatically optimize transformations based on Hermes usage. ([#24672](https://github.com/expo/expo/pull/24672) by [@EvanBacon](https://github.com/EvanBacon))
+- Enable `expo-router` Babel features when available. ([#24779](https://github.com/expo/expo/pull/24779) by [@EvanBacon](https://github.com/EvanBacon))
 
 ### 🐛 Bug fixes