nixosMod: add assertions/efi

nix/nixos-modules/assertions/default.nix

@@ -1,6 +1,7 @@
 {
   imports = [
     # files
+    ./efi.nix
     ./fileSystems.nix
     ./mdns.nix
     ./nixos.nix

nix/nixos-modules/assertions/efi.nix

@@ -0,0 +1,39 @@
+{
+  config,
+  lib,
+  options,
+  ...
+}:
+let
+  inherit (lib.strings) escapeNixString;
+  cfg = config.boot.loader;
+  fs = config.fileSystems;
+  efiIndicator = builtins.any (x: x) [
+    (cfg.grub.enable && cfg.grub.efiSupport)
+    (cfg.systemd-boot.enable)
+  ];
+  efiMountPath = escapeNixString cfg.efi.efiSysMountPoint;
+  efiMount = fs.${cfg.efi.efiSysMountPoint} or null;
+in
+# TODO check cfg.grub.mirroredBoots as well
+# TODO enable disko checks (optional i.e. when disko options are available)
+{
+  config = lib.mkIf efiIndicator {
+
+    assertions = [
+      {
+        assertion = efiMount != null;
+        message = ''
+          There is no filesystem declaration for EFI System Partition ${efiMountPath}
+        '';
+      }
+      {
+        assertion = efiMount != null -> efiMount.fsType == "vfat";
+        message = ''
+          EFI System Partition ${efiMountPath} has not fsType "vfat"
+        '';
+      }
+    ];
+
+  };
+}