nixos/hound: restart service on config changes

I expect config changes to be observable in the running service after
`sudo nixos-rebuild switch`. hound doesn't seem to support *reload*, so
use restart instead.

Author: bjornfor

nixos/modules/services/search/hound.nix

@@ -7,6 +7,13 @@
 let
   cfg = config.services.hound;
   settingsFormat = pkgs.formats.json { };
+  houndConfigFile = pkgs.writeTextFile {
+    name = "hound-config";
+    text = builtins.toJSON cfg.settings;
+    checkPhase = ''
+      ${cfg.package}/bin/houndd -check-conf -conf $out
+    '';
+  };
 in
 {
   imports = [
@@ -96,13 +103,7 @@ in
       };
     };
 
-    environment.etc."hound/config.json".source = pkgs.writeTextFile {
-      name = "hound-config";
-      text = builtins.toJSON cfg.settings;
-      checkPhase = ''
-        ${cfg.package}/bin/houndd -check-conf -conf $out
-      '';
-    };
+    environment.etc."hound/config.json".source = houndConfigFile;
 
     services.hound.settings = {
       dbpath = "${config.services.hound.home}/data";
@@ -112,6 +113,7 @@ in
       description = "Hound Code Search";
       wantedBy = [ "multi-user.target" ];
       after = [ "network.target" ];
+      restartTriggers = [ houndConfigFile ];
       serviceConfig = {
         User = cfg.user;
         Group = cfg.group;