nixosMod: extract nixos extends into assertions

nix/nixos-modules/assertions/default.nix

@@ -0,0 +1,6 @@
+{
+  imports = [
+    # files
+    ./nixos.nix
+  ];
+}

nix/nixos-modules/assertions/nixos.nix

@@ -3,7 +3,8 @@ let
   channelsEn = config.nix.channel.enable;
   nixFeature = lib.trivial.flip builtins.elem config.nix.settings.experimental-features;
   packageNames = map lib.strings.getName config.environment.systemPackages;
-  gitInst = builtins.elem "git" packageNames;
+  isInstalled = lib.trivial.flip builtins.elem packageNames;
+  gitInst = isInstalled "git";
   gitEn = config.programs.git.enable;
 in
 {

nix/nixos-modules/default.nix

@@ -12,11 +12,16 @@ in
 
   default = self.withDepends;
 
+  # assertions checking for good practices
+  assertions = importModule ./assertions;
+
   # this one includes all of my modules
   # - most of them only change things when enabled (e.g. x-banananetwork.*.enable)
   # - others only introduce small, reasonable changes if other module’s options are set, as reasonable defaults (if I intend to upstream them)
   # however, use on your own discretion
   banananetwork.imports = [
+    # flake
+    self.assertions
     # directories
     ./extends
     ./frontend

nix/nixos-modules/extends/default.nix

@@ -1,7 +1,6 @@
 {
   imports = [
     # files
-    ./nixos.nix
     ./podman.nix
   ];
 }