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Keep your local builds

DevHub is also an Expo build cache provider. With it, npx expo run:android and npx expo run:ios store each new build in the DevHub store. The next run with the same native code installs the stored build, and Gradle or Xcode does not run.

Set it up​

  1. Add DevHub to the project as a dev dependency. Expo CLI loads the provider from the project folder, not from a global install.

    npm install --save-dev @rootnative/devhub

  2. Add the provider to the app config (app.json or app.config.js):

    {
      "expo": {
        "buildCacheProvider": { "plugin": "@rootnative/devhub/cache-provider" }
      }
    }

    Expo SDK 53 reads the key under expo.experiments.

  3. Run the app as usual:

    npx expo run:android

The first run builds the app, and DevHub stores the APK. The next run with the same native code installs the stored APK. iOS works the same for a simulator.

What you see​

The provider writes its lines in the output of Expo CLI, with the prefix › DevHub:. When it has nothing to say, it writes nothing.

When a stored build serves a run​

A stored build serves a run when all of these agree:

  • The fingerprint of the platform. DevHub calculates it with the @expo/fingerprint of the project, the same as devhub match.
  • The variant. The Android --variant (default debug), or the iOS --configuration (default Debug).
  • Android: the native code. A debug build of npx expo run:android holds only the ABI of the device that it was made for. So the APK must have native code for each ready device. With --device <name>, DevHub checks only that device. With --all-arch, the APK must hold all four ABIs.
  • iOS: the Mac. A Mac with the same architecture made the build.

The newest build that fits wins. The project folder is not part of the match, so two clones of one project share their builds.

When DevHub is not sure that a stored build fits, Expo CLI builds the app. A wrong build is worse than a new build.

Limits​

  • Expo CLI uses a build cache provider only for npx expo run:*, and on iOS only for a simulator. It does not use it for an iOS device.
  • --binary turns the provider off for one run.
  • DevHub does not use or store a build of a run with --scheme.
  • Only builds that npx expo run:* made serve a run. A build that devhub sync downloaded from EAS does not.
  • The provider uses no network, never uninstalls an app, and never deletes a build.
  • When DevHub cannot read or write the store, it gives a warning, and the run continues.

After a change to the app config​

In a managed project, git ignores the android and ios folders, and the fingerprint does not read them. Expo CLI runs prebuild only when the folder is missing. So after a change to the app config, npx expo run:* builds the old native code with the new fingerprint.

DevHub does not store such a build. When app.json or app.config.* is newer than the last prebuild, it gives a warning. To fix it, do one of these:

  • Delete the android or ios folder, and run again.
  • Run npx expo prebuild --clean, and run again.

See the local builds​

devhub list shows a local build with the profile local and its variant, for example local debug. devhub match shows it as a match, and devhub install installs it the same as an EAS build.