nix: Add flake shell and build

.envrc

@@ -0,0 +1 @@
+use flake

.github/workflows/ci-nix.yml

@@ -0,0 +1,16 @@
+name: "CI Nix"
+on:
+  pull_request:
+  push:
+
+jobs:
+  check:
+    name: Rust project
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - name: Install Nix
+      uses: DeterminateSystems/nix-installer-action@main
+    - run: nix develop -c rustc --version
+    - run: nix build
+    - run: nix run || true

.gitignore

@@ -6,3 +6,6 @@ venv/
 qmk_gui.spec
 build/
 dist/
+
+# Nix
+result

README.md

@@ -193,3 +193,21 @@ Pre-requisites: Rust, libudev
 cargo build
 ls -l target/debug/qmk_hid
 ```
+
+###### With Nix Flakes
+
+Pre-requisites: Nix with flakes and nix command enabled.
+
+```
+# Build
+nix build
+
+# Build and run command
+nix run
+
+# Build and enter shell with command
+nix shell
+
+# Enter shell with cargo and dependencies
+nix develop
+```

flake.nix

@@ -0,0 +1,33 @@
+{
+  inputs = {
+    flake-utils.url = "github:numtide/flake-utils";
+    naersk.url = "github:nix-community/naersk";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+  };
+
+  outputs = { self, flake-utils, naersk, nixpkgs }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = (import nixpkgs) {
+          inherit system;
+        };
+
+        naersk' = pkgs.callPackage naersk {};
+
+      in rec {
+        # For `nix build` & `nix run`:
+        defaultPackage = naersk'.buildPackage {
+          src = ./.;
+          doCheck = false;
+          buildInputs = [ pkgs.systemd ];
+          nativeBuildInputs = [ pkgs.pkg-config ];
+        };
+
+        # For `nix develop` (optional, can be skipped):
+        devShell = pkgs.mkShell {
+          buildInputs = [ pkgs.systemd ];
+          nativeBuildInputs = with pkgs; [ rustc cargo pkg-config ];
+        };
+      }
+    );
+}

shell.nix

@@ -0,0 +1 @@
+(builtins.getFlake ("git+file://" + toString ./.)).devShells.${builtins.currentSystem}.default