emacs-android-nix

Nix flake for building GNU Emacs for Android with optional Nix package manager integration.

Project Goals

1. emacs-android: Reproducible build of upstream GNU Emacs for Android (unmodified)
2. emacs-android-termux: Emacs + Termux fork pair with shared storage (matching developer ID/signing key)
3. emacs-android-nix: Emacs + nix-on-droid pair with shared storage
4. emacs-nix-android: Emacs with built-in Nix package manager (no companion terminal app)
5. Sample configurations: Ready-to-use Emacs configs for Android with dependencies

Status

• Goal 1: Basic Emacs Android build
• Goal 2: Emacs + Termux shared storage
• Goal 3: Emacs + nix-on-droid shared storage
• Goal 4: Emacs with embedded Nix
• Goal 5: Sample configurations

Quick Start

# Enter development shell
nix develop

# Build Emacs for Android (arm64)
just build-emacs-arm64

# Build nix-on-droid with matching sharedUserId
just build-nod

# Verify both APKs have matching certificates
just verify-all

# Install both to connected Android device
just install-both

Architecture

emacs-android-nix/
├── flake.nix                    # Main flake (packageName, sharedUserId config)
├── keys/
│   └── debug.keystore           # Shared signing key for both APKs
├── packages/
│   ├── default.nix              # Package wiring
│   └── by-name/
│       ├── emacs-android/       # Emacs Android derivation
│       │   └── package.nix
│       └── nix-on-droid-app/    # nix-on-droid with patched sharedUserId
│           └── package.nix
├── Justfile                     # Build/install/verify recipes
└── .config/
    ├── android.nix              # Android SDK/NDK setup
    └── devshells/               # Development shell

Available Packages

Package	Description
emacs-android-arm64	Emacs for arm64 devices (default)
emacs-android-armv7	Emacs for older ARM devices
emacs-android-x86_64	Emacs for emulators
nix-on-droid-app	nix-on-droid with matching sharedUserId

Shared Storage

Both Emacs and nix-on-droid are configured to share storage:

• Same sharedUserId: org.gnu.emacs
• Same signing certificate: keys/debug.keystore

This allows both apps to access each other's internal storage at /data/data/org.gnu.emacs/.

Customization

Edit flake.nix to change the package ID:

packageName = "org.gnu.emacs";    # Change to your own ID
sharedUserId = "org.gnu.emacs";   # Must match for shared storage

If you change these, regenerate the keystore:

just gen-keystore

Useful Commands

# Build
just build-emacs-arm64           # Build Emacs APK
just build-nod                   # Build nix-on-droid APK

# Verify
just verify-all                  # Full verification (sharedUserId + certs)
just compare-certs               # Compare signing certificates
just show-cert <apk>             # Show certificate for any APK

# Install
just install-both                # Install both APKs
just install-emacs               # Install Emacs only
just install-nod                 # Install nix-on-droid only

# Emulator
just create-avd                  # Create test AVD
just emulator                    # Start headless emulator
just emulator-gui-direct         # Start GUI emulator

Build Requirements

• Nix with flakes enabled
• Linux x86_64 host (cross-compilation to Android)
• ~10GB disk space for Android SDK/NDK

Android Support Matrix

Package	Min API	Architecture	Notes
emacs-android	21 (5.0)	arm64-v8a	Primary target
emacs-android	21 (5.0)	armeabi-v7a	Legacy ARM
emacs-android	21 (5.0)	x86_64	Emulators

References

• GNU Emacs
• Emacs Android INSTALL
• nix-on-droid
• nix-on-droid-app
• F-Droid Emacs

License

GPL-3.0-or-later (same as GNU Emacs)