Metro can't resolve transitive dependencies when using bun as package manager

Summary

When using bun as package manager, Metro bundler cannot resolve transitive dependencies because bun stores them in node_modules/.bun/ rather than hoisting them to node_modules/.

Related

• https://github.com/expo/expo/issues/41994 - The debugging experience issue (how I discovered this)
• https://github.com/expo/expo/issues/41991

Steps to reproduce

1. Create an Expo project using bun as package manager
2. Have code that imports a transitive dependency (e.g., promise which is a dependency of react-native)
3. Run expo run:ios or expo start

Expected behavior

Metro should be able to resolve promise since it's a dependency of react-native which is installed.

Actual behavior

Unable to resolve module promise/setimmediate/rejection-tracking from /path/to/file.ts:
promise/setimmediate/rejection-tracking could not be found within the project or in these directories:
  node_modules
  ../node_modules

The package exists at node_modules/.bun/promise@8.3.0/node_modules/promise but Metro doesn't look there.

Workaround

Add transitive dependencies as direct dependencies in package.json:

"promise": "^8.3.0"

Environment

• bun: 1.x
• expo: 54.0.30
• react-native: 0.81.5

Possible solutions

1. Metro could be configured to also look in node_modules/.bun/
2. Expo/RN could list commonly-needed transitive deps like promise as peerDependencies
3. Documentation warning about bun compatibility

Notes

This differs from npm/yarn behavior where transitive dependencies are hoisted to root node_modules/ and are resolvable by any package. Bun is increasingly popular so this may affect more users.

Reproduce the failure with bun using expo run:ios or expo start, importing the transitive promise dependency. Start by tracing Metro's module resolution and compare its search paths with node_modules/.bun/. Done means the transitive dependency resolves under bun without requiring it to be added directly to package.json.