nixos/kanata: do not use path activation

Since 1.2.0, kanata handles missing keyboards well:
- only one keyboard need to be present when kanata starts;
- if linux-continue-if-no-devs-found is set to yes, all keyboards can
be missing at the beginning;
- all keyboards can be (un)pluged when kanata is running.

For simplicity, linux-continue-if-no-devs-found is set to yes and
systemd patch activation is removed.

nixos/modules/services/hardware/kanata.nix

@@ -11,16 +11,7 @@ let
         type = types.addCheck (types.listOf types.str)
           (devices: (length devices) > 0);
         example = [ "/dev/input/by-id/usb-0000_0000-event-kbd" ];
-        # TODO replace note with tip, which has not been implemented yet in
-        # nixos/lib/make-options-doc/mergeJSON.py
-        description = mdDoc ''
-          Paths to keyboard devices.
-
-          ::: {.note}
-          To avoid unnecessary triggers of the service unit, unplug devices in
-          the order of the list.
-          :::
-        '';
+        description = mdDoc "Paths to keyboard devices.";
       };
       config = mkOption {
         type = types.lines;
@@ -53,8 +44,12 @@ let
         default = "";
         example = "danger-enable-cmd yes";
         description = mdDoc ''
-          Configuration of `defcfg` other than `linux-dev`. See [example
-          config files](https://github.com/jtroo/kanata) for more information.
+          Configuration of `defcfg` other than `linux-dev` (generated
+          from the devices option) and
+          `linux-continue-if-no-devs-found` (hardcoded to be yes).
+
+          See [example config files](https://github.com/jtroo/kanata)
+          for more information.
         '';
       };
       extraArgs = mkOption {
@@ -81,20 +76,14 @@ let
   mkConfig = name: keyboard: pkgs.writeText "${mkName name}-config.kdb" ''
     (defcfg
       ${keyboard.extraDefCfg}
-      linux-dev ${mkDevices keyboard.devices})
+      linux-dev ${mkDevices keyboard.devices}
+      linux-continue-if-no-devs-found yes)
 
     ${keyboard.config}
   '';
 
   mkService = name: keyboard: nameValuePair (mkName name) {
-    description = "kanata for ${mkDevices keyboard.devices}";
-
-    # Because path units are used to activate service units, which
-    # will start the old stopped services during "nixos-rebuild
-    # switch", stopIfChanged here is a workaround to make sure new
-    # services are running after "nixos-rebuild switch".
-    stopIfChanged = false;
-
+    wantedBy = [ "multi-user.target" ];
     serviceConfig = {
       ExecStart = ''
         ${cfg.package}/bin/kanata \
@@ -146,33 +135,6 @@ let
       UMask = "0077";
     };
   };
-
-  mkPathName = i: name: "${mkName name}-${toString i}";
-
-  mkPath = name: n: i: device:
-    nameValuePair (mkPathName i name) {
-      description =
-        "${toString (i+1)}/${toString n} kanata trigger for ${name}, watching ${device}";
-      wantedBy = optional (i == 0) "multi-user.target";
-      pathConfig = {
-        PathExists = device;
-        # (ab)use systemd.path to construct a trigger chain so that the
-        # service unit is only started when all paths exist
-        # however, manual of systemd.path says Unit's suffix is not ".path"
-        Unit =
-          if (i + 1) == n
-          then "${mkName name}.service"
-          else "${mkPathName (i + 1) name}.path";
-      };
-      unitConfig.StopPropagatedFrom = optional (i > 0) "${mkName name}.service";
-    };
-
-  mkPaths = name: keyboard:
-    let
-      n = length keyboard.devices;
-    in
-    imap0 (mkPath name n) keyboard.devices
-  ;
 in
 {
   options.services.kanata = {
@@ -201,14 +163,7 @@ in
   config = mkIf cfg.enable {
     hardware.uinput.enable = true;
 
-    systemd = {
-      paths = trivial.pipe cfg.keyboards [
-        (mapAttrsToList mkPaths)
-        concatLists
-        listToAttrs
-      ];
-      services = mapAttrs' mkService cfg.keyboards;
-    };
+    systemd.services = mapAttrs' mkService cfg.keyboards;
   };
 
   meta.maintainers = with maintainers; [ linj ];