home-manager/meta: add home-manager-auto-expire.nix

home-manager/meta/default.nix

@@ -6,6 +6,7 @@
     ../../overlays
     ../../modules/device.nix
     ../../modules/meta.nix
+    ./home-manager-auto-expire.nix
   ];
 
   # Inherit config from NixOS or homeConfigurations
@@ -48,6 +49,13 @@
     git.enable = true;
   };
 
+  services.home-manager.autoExpire = lib.mkIf pkgs.stdenv.isLinux {
+    enable = true;
+    timestamp = "-7 days";
+    frequency = "3:05";
+    store.cleanup = true;
+  };
+
   # This value determines the Home Manager release that your
   # configuration is compatible with. This helps avoid breakage
   # when a new Home Manager release introduces backwards

home-manager/meta/home-manager-auto-expire.nix

@@ -0,0 +1,92 @@
+{ config, lib, pkgs, ... }:
+
+# TODO: Remove once merged
+# https://github.com/nix-community/home-manager/pull/4448
+let
+  cfg = config.services.home-manager.autoExpire;
+in
+{
+  options = {
+    services.home-manager.autoExpire = {
+      enable = lib.mkEnableOption ''
+        the Home Manager expire service that periodically expire your
+        old Home Manager generations'';
+
+      timestamp = lib.mkOption {
+        type = lib.types.str;
+        default = "-30 days";
+        example = "-7 days";
+        description = ''
+          Remove generations older than TIMESTAMP where TIMESTAMP is
+          interpreted as in the -d argument of the date tool.
+        '';
+      };
+
+      frequency = lib.mkOption {
+        type = lib.types.str;
+        default = "monthly";
+        example = "weekly";
+        description = ''
+          The interval at which the Home Manager auto expire is run.
+          This value is passed to the systemd timer configuration
+          as the `OnCalendar` option.
+          The format is described in
+          {manpage}`systemd.time(7)`.
+        '';
+      };
+
+      store = {
+        cleanup = lib.mkEnableOption ''
+          to cleanup Nix store when the Home Manager expire service runs.
+          It will use `nix-collect-garbage` to cleanup the store,
+          removing all unreachable store objects from the current user
+          (i.e.: not only the expired Home Manager generations).
+          This may not be what you want, this is why this option is disabled
+          by default.'';
+
+        options = lib.mkOption {
+          type = lib.types.str;
+          description = ''
+            Options given to `nix-collection-garbage` when the service runs.
+          '';
+          default = "";
+          example = "--delete-older-than 30d";
+        };
+      };
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    assertions = [
+      (lib.hm.assertions.assertPlatform "services.home-manager.autoExpire" pkgs
+        lib.platforms.linux)
+    ];
+
+    systemd.user = {
+      timers.home-manager-auto-expire = {
+        Unit.Description = "Home Manager expire generations timer";
+
+        Install.WantedBy = [ "timers.target" ];
+
+        Timer = {
+          OnCalendar = cfg.frequency;
+          Unit = "home-manager-auto-expire.service";
+          Persistent = true;
+        };
+      };
+
+      services.home-manager-auto-expire = {
+        Unit.Description = "Home Manager expire generations";
+
+        Service.ExecStart = toString
+          (pkgs.writeShellScript "home-manager-auto-expire" (''
+            echo "Expire old Home Manager generations"
+            ${pkgs.home-manager}/bin/home-manager expire-generations '${cfg.timestamp}'
+          '' + lib.optionalString cfg.store.cleanup ''
+            echo "Clean-up Nix store"
+            ${pkgs.nix}/bin/nix-collect-garbage ${cfg.store.options}
+          ''));
+      };
+    };
+  };
+}