expo-github-action

continuous-deploy-fingerprint is a GitHub Action designed for continuous deployment of Expo projects using the expo-updates fingerprint runtime version policy.

When executed, the action performs the following steps for each platform (iOS and Android):

1. Fingerprint Check: Determines the current fingerprint of the project.
2. Build Verification: Checks for existing EAS builds (in-progress or finished) that match the current fingerprint and the specified profile.
3. Conditional Build: If no matching build is found, it starts a new EAS build. It can optionally submit these builds to app stores.
4. Update Publication: Publishes an update to EAS Update.
5. PR Feedback: If running on a Pull Request, it posts a comment summarizing the actions taken.

The expo/expo-github-action/preview-comment subaction allows you to automatically comment on pull requests with Expo QR codes. This enables reviewers to load the app directly on their mobile devices.

Note: This action only creates the comment; it does not publish your project. You must run a publishing command (like expo publish) in a previous step.

      - name: 💬 Comment in preview
        uses: expo/expo-github-action/preview-comment@v8
        with:
          channel: pr-${{ github.event.number }}

The action exports the provided token to the environment to ensure you are authenticated for subsequent steps (like expo publish or eas build).

Important: The token is not stored by the action. Each separate workflow job must set up the token individually using the token input.

The action requires authentication to interact with the GitHub API (e.g., to post comments).

• Automatic Authentication: The action attempts to use the automatic token authentication provided by GitHub Actions by default.
• Manual Overrides: You can explicitly provide a token in two ways:
  1. Set the github-token input in the action configuration.
  2. Set the GITHUB_TOKEN environment variable.

The preview-build action uses @expo/fingerprint to determine if a pull request requires a new EAS Build.

• Fingerprint Compatible: If the fingerprint remains the same, it means no native code has changed, and the PR is compatible with existing EAS Updates. No new build is created.
• Fingerprint Changed: If the fingerprint changes, it indicates native code changes. The action will then execute the specified EAS Build command to create a new build.

This mechanism allows you to reuse existing builds and avoid unnecessary build costs and time when only JavaScript/assets change.

The action uses @actions/cache to restore previous installations of Expo and EAS CLI. This reduces installation time by downloading and extracting a single tar file instead of performing a fresh install.

Note: Using the cache counts towards your GitHub repository's cache limit. Expo and EAS CLI are stored in separate caches.