nixosConfiguration: preSwitchCkeck: nvd

Allow to specify a list of classes in the host/<hostname>.nix (by
default the class <hostname> is used) that will automatically load
specified outputs of inputs.

export/nixosConfigurations.nix

@@ -10,36 +10,58 @@
 { ... }@inputs:
 { host, ... }@imports:
 let
-  host' =
-    name: snippets:
-    let
+  pre-switch-check =
+    { pkgs, lib, config, ... }:
+    {
+      config.system.preSwitchChecks.nvd = ''
+        nvd_check=y
+        if [[ -d /run/current-system ]]
+        then
+          ${lib.getExe pkgs.nvd} --nix-bin-dir ${config.nix.package}/bin diff /run/current-system "''${1}"
+          if [[ -t 0 ]]; then
+            printf 'really %s to %s? [y]es/[N]o ' "''${2}" "''${1}"
+            read -r nvd_check
+          fi
+        fi
+        [[ "''${nvd_check}" == y ]]
+      '';
+    };
+
   system =
+    hostname:
     {
       namespace ? "fbs42",
       nixpkgs ? "nixpkgs",
+      classes ? [ hostname ],
     }:
     inputs.${nixpkgs}.lib.nixosSystem {
       specialArgs = { inherit inputs flake namespace; };
       modules =
         builtins.concatLists (
           map (
-                base: builtins.attrValues (flake.lib.scan { base = "${base}/host/${name}"; })
+            base: builtins.attrValues (flake.lib.scan { base = "${base}/host/${hostname}"; })
           ) flake.lib.schema.base
         )
-            ++ [ { config.networking.hostName = name; } ]
+        ++ map (class: {
+          imports = map (input: input.${namespace}.${class} or { }) (builtins.attrValues inputs);
+        }) classes
+        ++ [ pre-switch-check ]
+        ++ [ { config.networking.hostName = hostname; } ]
         ++ [ nixosModules.default ]
-            ++ [ inputs.home-manager.nixosModules.default ]
-            ++ [ { config.home-manager.sharedModules = [ hmModules.default ]; } ]
-            ++ [ { config.home-manager.extraSpecialArgs = { inherit flake namespace; }; } ]
+        ++ inputs.${nixpkgs}.lib.optional (inputs ? home-manager) {
+          imports = [ inputs.home-manager.nixosModules.default ];
+          config.home-manager = {
+            sharedModules = [ hmModules.default ];
+            extraSpecialArgs = { inherit flake namespace; };
+          };
+        }
         ++ builtins.attrValues nixosUsers
         ++ builtins.attrValues nixosGroups;
     };
 
-      cfg =
-        assert builtins.length snippets == 1;
-        builtins.head snippets;
-    in
-    system cfg;
-
 in
-builtins.mapAttrs host' host
+builtins.mapAttrs (
+  name: value:
+  assert builtins.length value == 1;
+  system name (builtins.head value)
+) host

flake.lock

@@ -1,61 +1,23 @@
 {
   "nodes": {
-    "hardware": {
-      "locked": {
-        "lastModified": 1753122741,
-        "narHash": "sha256-nFxE8lk9JvGelxClCmwuJYftbHqwnc01dRN4DVLUroM=",
-        "owner": "nixos",
-        "repo": "nixos-hardware",
-        "rev": "cc66fddc6cb04ab479a1bb062f4d4da27c936a22",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nixos",
-        "repo": "nixos-hardware",
-        "type": "github"
-      }
-    },
-    "home-manager": {
-      "inputs": {
-        "nixpkgs": [
-          "nixpkgs"
-        ]
-      },
-      "locked": {
-        "lastModified": 1757808926,
-        "narHash": "sha256-K6PEI5PYY94TVMH0mX3MbZNYFme7oNRKml/85BpRRAo=",
-        "owner": "nix-community",
-        "repo": "home-manager",
-        "rev": "f21d9167782c086a33ad53e2311854a8f13c281e",
-        "type": "github"
-      },
-      "original": {
-        "owner": "nix-community",
-        "ref": "release-25.05",
-        "repo": "home-manager",
-        "type": "github"
-      }
-    },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1757810152,
-        "narHash": "sha256-Vp9K5ol6h0J90jG7Rm4RWZsCB3x7v5VPx588TQ1dkfs=",
+        "lastModified": 1763966396,
+        "narHash": "sha256-6eeL1YPcY1MV3DDStIDIdy/zZCDKgHdkCmsrLJFiZf0=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "9a094440e02a699be5c57453a092a8baf569bdad",
+        "rev": "5ae3b07d8d6527c42f17c876e404993199144b6a",
         "type": "github"
       },
       "original": {
         "owner": "nixos",
-        "ref": "nixos-25.05",
+        "ref": "nixos-unstable",
         "repo": "nixpkgs",
         "type": "github"
       }
     },
     "root": {
       "inputs": {
-        "hardware": "hardware",
-        "home-manager": "home-manager",
         "nixpkgs": "nixpkgs"
       }
     }

flake.nix

@@ -1,12 +1,6 @@
 {
-  inputs = {
-    nixpkgs.url = "github:nixos/nixpkgs/nixos-25.05";
-    hardware.url = "github:nixos/nixos-hardware";
-    home-manager = {
-      url = "github:nix-community/home-manager/release-25.05";
-      inputs.nixpkgs.follows = "nixpkgs";
-    };
-  };
+  # only used for nixfmt-tree
+  inputs.nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
 
   outputs = { self, ... }@inputs: import ./lib/flake.nix inputs ./.;
 }