refactor: hide x86_64-specific host config in a module

hosts/common/default.nix

@@ -4,7 +4,6 @@
     ./boot.nix
     ./feeds.nix
     ./fs.nix
-    ./hardware
     ./home
     ./hosts.nix
     ./ids.nix

hosts/common/hardware/default.nix

@@ -1,17 +0,0 @@
-{ config, lib, pkgs, ... }:
-
-{
-  imports = [
-    ./x86_64.nix
-  ];
-
-  # services.snapper.configs = {
-  #   root = {
-  #     subvolume = "/";
-  #     extraConfig = {
-  #       ALLOW_USERS = "colin";
-  #     };
-  #   };
-  # };
-  # services.snapper.snapshotInterval = "daily";
-}

hosts/modules/default.nix

@@ -3,6 +3,7 @@
 {
   imports = [
     ./derived-secrets
+    ./hal
     ./hosts.nix
     ./nixcache.nix
     ./roles

hosts/modules/hal/default.nix

@@ -0,0 +1,6 @@
+{ ... }:
+{
+  imports = [
+    ./x86_64.nix
+  ];
+}

hosts/modules/hal/x86_64.nix

@@ -1,7 +1,14 @@
-{ lib, pkgs, ... }:
-
+{ config, lib, pkgs, ... }:
+let
+  cfg = config.sane.hal.x86_64;
+in
 {
-  config = lib.mkIf (pkgs.system == "x86_64-linux") {
+  options = {
+    sane.hal.x86_64.enable = (lib.mkEnableOption "x86_64-specific hardware support") // {
+      default = pkgs.system == "x86_64-linux";
+    };
+  };
+  config = lib.mkIf cfg.enable {
     boot.initrd.availableKernelModules = [
       "xhci_pci" "ahci" "sd_mod" "sdhci_pci"  # nixos-generate-config defaults
       "usb_storage"   # rpi needed this to boot from usb storage, i think.