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Contributing to the Expo SDK

Thanks for your interest in contributing! We currently review PRs for packages/, docs/, templates/, guides/, apps/, and markdown files.

We recommend that folks interested in contributing to the SDK use the apps/bare-expo project in their SDK development workflow instead of Expo Go (in apps/expo-go). The Expo Go app is difficult to set up and requires API tokens.

The bare-expo project includes most of the Expo SDK. It runs the JavaScript code from apps/test-suite and apps/native-component-list. That allows you to browse the Expo SDK components and APIs and easily write and run E2E tests for iOS, and Android for any given SDK package. Unit tests can be written within the SDK package itself. When pushed to the remote, CI will run this project with tests for Android/iOS and report the results on your pull request.

Manual smoke tests are included in apps/native-component-list, which is a good fit for demos or tests that require physical interactions. This is particularly useful if you are testing interactions with UI components, or if there is something very difficult to test in an automated way but would be easy to verify through manual interaction.

💡 How does bare-expo relate to test-suite?

bare-expo is a bare React Native app that links all of the Expo SDK dependencies in the packages/ directory in order to be able to run projects in the apps/ directory. It currently runs test-suite (an Expo app with some custom code to turn it into a test runner), and native-component-list. If you run expo start in the test-suite directory you can load the project in Expo Go. bare-expo imports the test-suite app root component and uses it as its own root component.

📦 Download and Setup

💽 The development environment for this repository does not support Windows; WSL is required to contribute from Windows.

  1. If you are an Expo team member, clone the repository. If you are an external contributor, fork this repository to your own GitHub account and then clone it to your local device. (git remote add upstream git@github.com:expo/expo.git 😉). You can use git clone --depth 1 --single-branch --branch main git@github.com:expo/expo.git, skipping most of the branches and history to clone it faster.
  2. Install direnv. On macOS: brew install direnv. Don't forget to install the shell hook to your shell profile.
  3. Install git-lfs. On macOS: brew install git-lfs.
  4. Install Node LTS.

Set up documentation

If you plan to contribute to the documentation, run npm run setup:docs.

Set up Android

If you plan to contribute to Android, run npm run setup:native. This command does the following for you:

  • Downloads submodules (like react-native) with git submodule update --init
  • Ensures Yarn is installed
  • Ensures your computer is set up for React Native (will install the Android NDK if it's not present)
  • Downloads the Node packages (yarn install)

We recommend JDK 17 (eg. zulu17). Run the following commands in a terminal window to install it:

brew tap homebrew/cask-versions
brew install --cask zulu@17

After you install the JDK, add the JAVA_HOME environment variable in ~/.bash_profile (or ~/.zshrc if you use ZSH):

export JAVA_HOME=/Library/Java/JavaVirtualMachines/zulu-17.jdk/Contents/Home

ANDROID_SDK_ROOT environmental variable should be set or configured via local.properties file in android folder of the native project you're working with.

Set up iOS

If you will be working with the iOS project, ensure ruby 2.7 is installed on your machine. macOS comes with ruby 2.6, which is not supported in this repository; if you use Homebrew you can just run brew install ruby@2.7. You will also need to have the latest stable version of Xcode installed, along with Xcode command line tools.

Verify native installation is successful

  1. Navigate to the bare sandbox project cd apps/bare-expo

  2. Run the project on any native platform:

    • iOS: yarn ios
    • Android: yarn android
    • If you are working on Linux, make sure to set the TERMINAL environment variable to your preferred terminal application. (e.g. export TERMINAL="konsole")

  3. You are now running the test-suite app via the bare-expo project. The next section explains how you can begin to make changes to SDK packages.

If this didn't work for you as described, please open an issue.

✍️ Editing SDK Packages

All Expo SDK packages can be found in the packages/ directory. These packages are automatically linked to the projects in the apps/ directory, so you can edit them in-place and see the changes in the running app.

  1. Navigate to a package you want to edit. Ex: cd packages/expo-constants
  2. Start the TypeScript build in watch mode: yarn build
  3. Edit code in that package's src/ directory
  4. Play with your changes on a simulator or device through bare-expo:
    • Add or modify a file named after the API you're working on. Ex: apps/test-suite/tests/Constants.js
    • To see native changes, you will need to run the test-suite with the apps/bare-expo project using yarn <android | ios>.
    • If you are only making JavaScript changes, you can run test-suite from the apps/test-suite project using expo start.
    • To run the full test suite, you can run the tests yarn test:<android | ios>.
  5. You can edit a package's native code directly from its respective folder in the packages/ directory or by opening bare-expo in a native editor:
    • Navigate to the bare-expo app directory: cd apps/bare-expo
    • Android Studio: yarn edit:android
    • Xcode: yarn edit:ios
    • Remember to rebuild the native project whenever you make a native change

Finding a task to work on

If you don't have something in mind already, the best way to find something to help with is "Issue accepted" label.

Note that we generally do not accept PRs that bump versions of native dependencies. The Expo team handles bumping these dependencies as part of our release process for each Expo SDK. The process for pulling in a new version and adequately requires a fair amount of context on how Expo Go works.

Style

All modules should adhere to the style guides which can be found here:

Extra Credit

  • The React Native dev tools are currently disabled in our fork #5602. You can hack around this by cloning React Native outside this repo, then copying the contents react-native/React/DevSupport into expo/react-native-lab/react-native/React/DevSupport (this will only enable the shake gesture, CMD+R won't work yet).
  • We use a fork of react-native in this repo; this fork is located at react-native-lab/react-native (you can make changes or cherry-picks from here if you want). It diverges the minimal amount necessary from the react-native version in its package.json.
  • All of the package's build/ code should be committed. This is because it is simpler to reproduce issues if all contributors are running the same code and so we don't need to rebuild dozens of packages locally on every git pull or git checkout operation.
  • We use a unified set of basic Bash scripts and configs called expo-module-scripts to ensure everything runs smoothly (TypeScript, Babel, Jest, etc...).

⏱ Testing Your Changes

You'll need write about how you tested your changes in the PR under the Test Plan section.

The best way to get your changes merged is to build good tests for them! We have three different kinds of tests: unit-tests, automated E2E tests, and demos (adding tests that you notice are missing is a great way to become my friend 🥳)!

✅ Unit Testing

  1. Create a test for your feature in the appropriate package's src/__tests__ directory (if the file doesn't exist already, create it with the *-test.ts or *-test.tsx extension).
  2. Any new bridged native functions have to be added to the jest-expo package to ensure they are mocked. To help you do this more easily, we've written a tool and a guide on how to do this. Check out Generating Jest Mocks!
  3. Run the test with yarn test and ensure it handles all platforms (iOS, Android, and web). If the feature doesn't support a platform, then you can exclude it by putting your test in a file with a platform extension like: .test.ios.ts, .test.native.ts, .test.web.ts...
  4. You can also test platforms one at a time by pressing X and selecting the platform you want to test!

🏁 E2E Testing

  1. Write your tests in apps/test-suite/tests
    • These tests are written with a non-feature-complete version of Jasmine that runs on the Android and iOS clients, so no special features like snapshot testing will be available.
    • If you created a new test file, be sure to add it in apps/test-suite/TestUtils.js.
    • If the new test file could be running automatically from the bare-expo testing, add it in apps/bare-expo/e2e/TestSuite-test.native.js.
  2. Run your tests locally from the bare-expo directory with yarn test:android, or yarn test:ios.
    • It's important you test locally because native CI tests can be fragile, take a while to finish, and be frustrating when they fail.
  3. Remember to try and get your feature running on as many platforms as possible.

Thanks again for helping to make sure that Expo is stable for everyone!

📚 Updating Documentation

Our docs are made with Next.js. They're located in the docs directory. For more information look at the docs/README.md.

TL;DR:

  1. Navigate to the docs directory and run yarn.
  2. Start the project with yarn dev (make sure you don't have another server running on port 3002).
  3. Navigate to the docs you want to edit: cd docs/pages/.
  4. If you update an older version, ensure the relevant changes are copied into docs/pages/versions/unversioned/ for API docs.

📝 Writing a Commit Message

If this is your first time committing to a large public repo, you could look through this neat tutorial: "How to Write a Git Commit Message"

Commit messages are most useful when formatted like so: [platform][api] Title. For example, if you fix a bug in the package expo-video for iOS, you could write: [ios][video] Fixed black screen bug that appears on older devices.

🔎 Before Submitting

To help keep CI green, please make sure of the following:

  • Remember to add a concise description of any user-facing changes to CHANGELOG.md file in the package you've changed or root's CHANGELOG.md if your changes don't apply to any package. This is especially helpful for breaking changes!
  • If you modified anything in packages/:
    • You transpiled the TypeScript with yarn build in the directory of whichever package you modified.
    • Run yarn lint --fix to fix the formatting of the code. Ensure that yarn lint succeeds without errors or warnings.
    • Run yarn test to ensure all existing tests pass for that package, along with any new tests you would've written.
    • All console.logs or commented out code blocks are removed!
  • If you edited the docs directory:
    • Any change to the current SDK version should also be in the unversioned copy as well. Example:
      • You fixed a typo in docs/pages/versions/vXX.0.0/sdk/app-auth.md
      • Ensure you copy that change to: docs/pages/versions/unversioned/sdk/app-auth.md
    • You don't need to run the docs tests locally. Just ensure the links you include aren't broken, the format is correct, and the changes are following our writing style guide.

Extra Credit

  • Our CI tests will finish early if you don't make changes to certain directories. If you want to get results faster then you should make changes to docs directory in one PR, and changes to anything else in another!