Error when using with metro only

[wallzero]

Before submitting a new issue

• I tested using the latest version of the library, as the bug might be already fixed.
• I tested using a supported version of react native.
• I checked for possible duplicate issues, with possible answers.

Bug summary

The instructions in the README.md state:

Non-Expo Projects

react-native-css relies on the bundler to process CSS files. Currently only Expo provides a CSS asset pipeline. Since the Expo SDK is modular, you can add this functionality by just using the @expo/metro-config package.

Follow the Expo instructions, but replace the expo package with @expo/metro-config.

When I try this I receive an error:

error Error loading Metro config at: metro.config.js
Cannot find module 'expo/package.json'
Require stack:
- node_modules/@expo/metro-config/build/transform-worker/utils/moduleMapper.js

Is there a specific version of @expo/metro-config I should be using? I'd like to avoid importing all of expo.

Library version

3.0.7

Environment info

System:
  OS: Linux 7.0
  CPU: 
  Memory: GB
  Shell:
    version: 5
    path: /bin/sh
Binaries:
  Node:
    version: 24.15.0
    path: 
  Yarn:
    version: 1.22.22
    path: 
  npm:
    version: 11.13.0
    path: 
  Watchman: Not Found
SDKs:
  Android SDK: Not Found
IDEs:
  Android Studio: Not Found
Languages:
  Java:
    version: 17.0.19
    path: 
  Ruby: Not Found
npmPackages:
  "@react-native-community/cli":
    installed: 20.1.3
    wanted: ^20.1.3
  react:
    installed: 19.2.3
    wanted: ^19.2.5
  react-native:
    installed: 0.85.3
    wanted: ^0.85.3
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: true
  newArchEnabled: true
iOS:
  hermesEnabled: true
  newArchEnabled: true

Steps to reproduce

1. npx @react-native-community/cli@latest init reactNativeCssExample --version latest
2. npm i --save-dev react-native-css @expo/metro-config
3. setup metro.config.js

const { mergeConfig } = require('@react-native/metro-config');
const { getDefaultConfig } = require('@expo/metro-config');

/**
 * Metro configuration
 * https://reactnative.dev/docs/metro
 *
 * @type {import('@react-native/metro-config').MetroConfig}
 */
const config = {};

module.exports = mergeConfig(
  getDefaultConfig(__dirname),
  config
);

4. npm run start

Reproducible example repository

https://github.com/wallzero/react-native-css-example

[github-actions]

🤖 Auto-triage

Status: NEEDS_TIER_2
Type: bug
Version: v3 (3.0.7)

Findings

This is a Metro/build configuration issue, not a CSS compilation or runtime bug. The error originates from @expo/metro-config itself (moduleMapper.js does require('expo/package.json')), and the current published @expo/metro-config@55.x declares expo as a peer dependency. The README's "Non-Expo Projects" guidance — to install only @expo/metro-config without expo — appears to be outdated for current Expo SDK versions, since @expo/metro-config now resolves expo/package.json at runtime.

What I tested

• Read the issue body and the linked repro steps (did not run the external repo).
• Inspected the project README (README.md lines 36-45) which contains the "Non-Expo Projects" guidance the reporter followed.
• Ran npm view @expo/metro-config version → 55.0.20.
• Ran npm view @expo/metro-config@55.0.20 peerDependencies → { expo: '*' }.
• Confirmed this is not Jest-reproducible (it's a Metro module resolution failure outside the CSS compiler/runtime).

Next steps

• Decide on the supported path for non-Expo Metro projects:
  • Option A: Update README to require expo as well (workaround the reporter wants to avoid).
  • Option B: Pin/document a known-working older @expo/metro-config version that didn't require expo/package.json.
  • Option C: Provide a first-party non-Expo CSS asset pipeline so this dependency on @expo/metro-config isn't needed.
• Tier 2 triage should validate against the reporter's repro repo (https://github.com/wallzero/react-native-css-example) and confirm which @expo/metro-config versions still work standalone.

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_{This is an automated triage. See auto-triage.yml.}