Add Nix flake configuration

lib/nixos.nix

@@ -0,0 +1,25 @@
+{ inputs, lib, pkgs, ... }:
+
+with lib;
+with lib.my;
+let sys = "x86_64-linux";
+in {
+  mkHost = path: attrs @ { system ? sys, ... }:
+    nixosSystem {
+      inherit system;
+      specialArgs = { inherit lib inputs system; };
+      modules = [
+        {
+          nixpkgs.pkgs = pkgs;
+          networking.hostName = mkDefault (removeSuffix ".nix" (baseNameOf path));
+        }
+        (filterAttrs (n: v: !elem n [ "system" ]) attrs)
+        ../.   # /default.nix
+        (import path)
+      ];
+    };
+
+  mapHosts = dir: attrs @ { system ? system, ... }:
+    mapModules dir
+      (hostPath: mkHost hostPath attrs);
+}