EAS Local Build Fails on macOS [Error and temporal Solution]

[joncodeofficial]

Description

EAS Local Build Fails on macOS — libworklets.so Missing

The Problem

When running npx eas build --platform android --local, the build fails with:

ninja: error: '...react-native-worklets/android/build/intermediates/cmake/release/obj/arm64-v8a/libworklets.so',
needed by '...libexpo-modules-core.so', missing and no known rule to make it

This only happens with EAS local builds on macOS. EAS Cloud builds and direct ./gradlew assembleRelease work fine.

Root Cause

On macOS, /tmp is a symlink to /private/tmp. EAS local builds copy the project to /tmp/eas-build-local-nodejs/... by default.

CMake and Ninja have a known bug where they mix logical paths (/tmp/...) with physical paths (/private/tmp/...) when resolving paths through symlinks. This causes Ninja to look for .so files at a path that doesn't match where they were actually built.

The Fix

Tell EAS to use a directory that isn't behind a symlink:

EAS_LOCAL_BUILD_WORKINGDIR=$HOME/tmp/eas-build npx eas build --platform android --local --profile preview

Or set it permanently in your shell (~/.zshrc):

export EAS_LOCAL_BUILD_WORKINGDIR="$HOME/tmp/eas-build"

Then run EAS local builds normally — no extra flags needed.

Affected Versions

• macOS (any version — /tmp -> /private/tmp symlink is universal)
• react-native-reanimated 4.x + react-native-worklets
• Any Expo SDK using expo-modules-core with native C++ dependencies
• Any AGP version

What Doesn't Work

• Patching expo-modules-core or react-native-reanimated Gradle files
• Disabling Gradle parallel builds (org.gradle.parallel=false)
• Setting ANDROID_NDK_HOME
• Changing CMake versions
• EAS build hooks (eas-build-post-install)

Related Issues

• expo/expo#40525
• software-mansion/react-native-reanimated#8506
• ninja-build/ninja#1330

Steps to reproduce

1. Create a new Expo project using npx create-expo-app myApp and navigate into it.

2. Install react-native-reanimated (version 4 or higher) using npx expo install react-native-reanimated.

3. Run npx expo prebuild to generate the native Android project.

4. Go into the android folder and run ./gradlew assembleRelease to confirm the project builds correctly with Gradle.

5. Install EAS CLI globally with npm install -g eas-cli if it is not already installed.

6. Run npx eas build:configure and set up the project for Android builds.

7. Execute a local EAS build using npx eas build --platform android --local.

8. Wait for the build to fail with a Ninja error indicating that libworklets.so is missing.

9. Verify that the build was executed inside /tmp/eas-build-local-nodejs/....

10. Confirm that /tmp is a symlink to /private/tmp on macOS, which causes the path resolution issue leading to the error.

Snack or a link to a repository

https://github.com/joncodeofficial

Reanimated version

4.0.0

Worklets version

0.6.1

React Native version

0.81.5

Platforms

iOS

JavaScript runtime

Hermes

Workflow

Expo Dev Client

Architecture

New Architecture (Fabric renderer)

Reanimated feature flags

None

React Native release level

Stable

Build type

No response

Device

Real device

Host machine

macOS

Device model

No response

Acknowledgements

Yes

[github-actions]

Hey! 👋

The issue doesn't seem to contain a minimal reproduction.

Could you provide a snack or a link to a GitHub repository under your username that reproduces the problem?

[github-actions]

Hey! 👋

It looks like you've omitted a few important sections from the issue template.

Please complete Description section.

[tjzel]

Hi @joncodeofficial, I tried to reproduce it on a project with the following dependencies and going step-by-step by your reproduction I didn't get any errors:

  "dependencies": {
    "eas-cli": "18.4.0",
    "expo": "~55.0.6",
    "expo-dev-client": "~55.0.16",
    "expo-status-bar": "~55.0.4",
    "react": "19.2.0",
    "react-dom": "19.2.0",
    "react-native": "0.83.2",
    "react-native-reanimated": "4.3.0",
    "react-native-web": "^0.21.0",
    "react-native-worklets": "0.8.1"
  },

Could you verify if it's still an issue for you with Reanimated 4.3.0 and Worklets 0.8.1?

[joncodeofficial]

Hi! Thanks for taking the time to test it 🙌

From what I’ve been able to observe so far, this issue seems to only happen on macOS when using Expo in bare workflow, specifically with EAS local builds.

Could you confirm if your setup matches that scenario?

macOS
Expo bare workflow (after expo prebuild)
Running npx eas build --platform android --local

In my case, the error does not appear when building directly with Gradle or using EAS Cloud — only with local builds on macOS, which makes me think it’s related to how the build environment is set up there (possibly the /tmp symlink issue).

[satishs22]

Any ideal solution for now?

[tjzel]

I tried it again just to be sure and it worked, but for me the build is done in the /var directory:

/var/folders/jg/m839qn593nn7w_h3n0r9k25c0000gn/T/eas-build-local-nodejs/1ea5ad37-1dd6-4591-a4aa-f5100230e143/build/android/app/build/outputs/bundle/release/app-release.aab

I'm afraid this is something related to your local setup than something that a library can fix.

[joncodeofficial]

Hey @tjzel, thanks for testing again!
The reason you can't reproduce it is likely that on your machine EAS is using /var/folders/... which is a real path — no symlinks involved. On some macOS setups EAS picks /tmp instead, and /tmp on macOS is always a symlink to /private/tmp. That's the key difference.
The CMake/Ninja path resolution bug (ninja-build/ninja#1330) only triggers when the build runs inside a symlinked directory, which is why:

Your setup works ✅
Cloud builds work ✅
Direct ./gradlew works ✅
My local EAS build fails ❌

Setting EAS_LOCAL_BUILD_WORKINGDIR=$HOME/tmp/eas-build fixes it completely because it forces EAS to use a real path.
I think this is worth documenting at least in the EAS local build docs, since /tmp vs /var behavior can vary between macOS versions or configurations and other users will hit this.

[tjzel]

Is this really something on the library side? I think it's more of a Expo framework build issue - the error happens when building Worklets but we have no say in where are the build files located etc.