handled by the nix-index enable module

nixos/home/jahanson/global.nix

@@ -45,7 +45,6 @@ with config;
         dbus
         direnv
         git
-        nix-index
         python3
         fzf
         ripgrep

nixos/modules/nixos/services/nix-index-daily/default.nix

@@ -0,0 +1,59 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+let
+  cfg = config.services.nix-index-daily;
+in
+{
+  options.services.nix-index-daily = {
+    enable = lib.mkEnableOption "Automatic daily nix-index database updates";
+
+    user = lib.mkOption {
+      type = lib.types.str;
+      description = "User account under which to run nix-index";
+      example = "alice";
+    };
+
+    startTime = lib.mkOption {
+      type = lib.types.str;
+      default = "daily";
+      description = "When to start the service. See systemd.time(7)";
+      example = "03:00";
+    };
+
+    randomizedDelaySec = lib.mkOption {
+      type = lib.types.int;
+      default = 3600;
+      description = "Random delay in seconds after startTime";
+      example = 1800;
+    };
+  };
+
+  config = lib.mkIf cfg.enable {
+    users.users.${cfg.user}.packages = [ pkgs.nix-index ];
+
+    systemd.user.services.nix-index-update = {
+      description = "Update nix-index database";
+      script = "${pkgs.nix-index}/bin/nix-index";
+      serviceConfig = {
+        Type = "oneshot";
+      };
+    };
+
+    systemd.user.timers.nix-index-update = {
+      wantedBy = [ "timers.target" ];
+      timerConfig = {
+        OnCalendar = cfg.startTime;
+        Persistent = true;
+        RandomizedDelaySec = cfg.randomizedDelaySec;
+      };
+    };
+
+    # Ensure the services are enabled
+    systemd.user.services.nix-index-update.enable = true;
+    systemd.user.timers.nix-index-update.enable = true;
+  };
+}