build nix-darwin in ci

.github/workflows/ci.yml

@@ -34,3 +34,14 @@ jobs:
     - uses: cachix/install-nix-action@v27
     - uses: DeterminateSystems/magic-nix-cache-action@v8
     - run: nix build '.#nixosConfigurations."${{ matrix.machine }}.nixos.org".config.system.build.toplevel'
+  nix-darwin:
+    runs-on: macos-latest
+    strategy:
+      matrix:
+        # Doesn't seem that x86_64 is still in use?
+        machine: [arm64]
+    steps:
+    - uses: actions/checkout@v4
+    - uses: cachix/install-nix-action@v27
+    - uses: DeterminateSystems/magic-nix-cache-action@v8
+    - run: nix build '.#darwinConfigurations."${{ matrix.machine }}".config.system.build.toplevel'

flake.nix

@@ -3,9 +3,15 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-24.05";
+    nixpkgs-unstable.url = "github:nixos/nixpkgs/nixpkgs-unstable";
     flake-parts.url = "github:hercules-ci/flake-parts";
     flake-parts.inputs.nixpkgs-lib.follows = "nixpkgs";
 
+    darwin = {
+      url = "github:LnL7/nix-darwin";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
     flake-utils.url = "github:numtide/flake-utils";
     treefmt-nix.url = "github:numtide/treefmt-nix";
 
@@ -54,6 +60,7 @@
         ./checks/flake-module.nix
         ./terraform/flake-module.nix
         ./non-critical-infra/flake-module.nix
+        ./macs/flake-module.nix
       ];
     };
 }

macs/flake-module.nix

@@ -0,0 +1,17 @@
+{ inputs, ... }:
+{
+  flake.darwinConfigurations =
+    let
+      mac =
+        system:
+        inputs.darwin.lib.darwinSystem {
+          inherit system;
+
+          modules = [ ./nix-darwin.nix ];
+        };
+    in
+    {
+      arm64 = mac "aarch64-darwin";
+      x86_64 = mac "x86_64-darwin";
+    };
+}