React Native Development Nix Environment Setup

This document outlines how to set up your React Native development environment using Nix flakes for reproducibility and isolation.

Disclaimer

This was tested on an Arch Linux system with AMD CPU and GPU. There are likely problems with NVIDIA GPUs.

Compatibility with Microsoft WSL2 is not guaranteed, but should work withoud major issues, except for the emulator.

Nix installed: https://nixos.org/download.html
Git: Required for cloning the repository.
KVM (for emulator, if enabled): Ensure KVM is enabled and your user is in the kvm group for optimal emulator performance:
```
sudo usermod -aG kvm $USER && newgrp kvm # (or log out/in)
kvm-ok # Verify KVM acceleration
```
GPU Drivers (for emulator, if enabled): For hardware-accelerated emulator (AMD/Intel), ensure host Vulkan drivers are working:
```
vulkaninfo | grep -i "device name" # Should show your GPU
```
If not, install vulkan-radeon (AMD) or vulkan-intel (Intel) on your host system and reboot.

Clone the Project:

git clone <your-fork-url>
cd <your-fork-name>

Enter the Development Shell:

If you have npm or yarn installed, use the defined scripts:
- For Physical Device Only (default):
```
npm run nix # or yarn nix
```
- For Emulator Development (explicitly enable):
```
npm run nix-emulator # or yarn nix-emulator
```
If you do not have npm/yarn installed, execute the commands manually:
- For Physical Device Only (default):
```
nix develop --extra-experimental-features nix-command --extra-experimental-features flakes
```
- For Emulator Development (explicitly enable):
```
nix develop .#emulator --extra-experimental-features nix-command --extra-experimental-features flakes
```
The first time, this will download and set up all required tools, which can take considerable time. Subsequent entries will be much faster. You will also see a message about "Setting up writable Android SDK..." which only happens once.

Once inside the nix develop shell, all tools are available.

Open a new terminal or run in the background:

npm start

Connect Device: Enable USB debugging on your Android device and connect it via USB.
Verify Device:
```
adb devices
```

Mirror Screen (Optional):

scrcpy # Mirrors screen, provides control
scrcpy -s <device_serial> # If multiple devices connected

Launch Emulator:
```
emulator -avd ReactNative_API35 -gpu host -no-metrics -no-audio
```
- Use -gpu swiftshader_indirect if hardware acceleration (-gpu host) fails.
Verify Emulator:
```
adb devices
```
Run App: Launches the the emulater automatically, if it is not already running.
```
npx run android
```