pinwheel: Automatically garbage collect generations

hosts/pinwheel/modules/boot/default.nix

@@ -1,21 +1,37 @@
-{ pkgs, ... }:
+{ inputs, pkgs, config, ... }:
 {
-  boot = {
-    kernelPackages = pkgs.linuxPackages_latest;
+  imports = [ inputs.nix-gc-env.nixosModules.default ];
 
-    kernel = {
-      sysctl = {
-        "fs.inotify.max_user_instances" = 1024; # default: 128
+  config = {
+    nix.gc = {
+      automatic = true;
+      dates = "weekly";
+
+      # `delete_generations` added by nix-gc-env
+      delete_generations = "+${builtins.toString config.boot.loader.systemd-boot.configurationLimit}";
+    };
+
+    boot = {
+      kernelPackages = pkgs.linuxPackages_latest;
+
+      kernel = {
+        sysctl = {
+          "fs.inotify.max_user_instances" = 1024; # default: 128
+        };
       };
-    };
 
-    loader = {
-      systemd-boot.enable = true;
-      efi.canTouchEfiVariables = true;
-    };
+      loader = {
+        systemd-boot = {
+          enable = true;
+          configurationLimit = 10;
+        };
 
-    initrd.secrets = {
-      "/crypto_keyfile.bin" = null;
+        efi.canTouchEfiVariables = true;
+      };
+
+      initrd.secrets = {
+        "/crypto_keyfile.bin" = null;
+      };
     };
   };
 }