mpd: add `extraArgs` (#3735)

Allow passing arguments to the MPD command line. Currently the only
interesting one is `--verbose`.

modules/services/mpd.nix

@@ -92,6 +92,15 @@ in {
         '';
       };
 
+      extraArgs = mkOption {
+        type = types.listOf types.str;
+        default = [ ];
+        example = [ "--verbose" ];
+        description = ''
+          Extra command-line arguments to pass to MPD.
+        '';
+      };
+
       dataDir = mkOption {
         type = types.path;
         default = "${config.xdg.dataHome}/${name}";
@@ -176,7 +185,9 @@ in {
 
       Service = {
         Environment = "PATH=${config.home.profileDirectory}/bin";
-        ExecStart = "${cfg.package}/bin/mpd --no-daemon ${mpdConf}";
+        ExecStart = "${cfg.package}/bin/mpd --no-daemon ${mpdConf} ${
+            escapeShellArgs cfg.extraArgs
+          }";
         Type = "notify";
         ExecStartPre = ''
           ${pkgs.bash}/bin/bash -c "${pkgs.coreutils}/bin/mkdir -p '${cfg.dataDir}' '${cfg.playlistDirectory}'"'';

tests/modules/services/mpd/basic-configuration.nix

@@ -6,6 +6,7 @@ with lib;
   services.mpd = {
     enable = true;
     musicDirectory = "/my/music/dir";
+    extraArgs = [ "--verbose" ];
   };
 
   home.stateVersion = "22.11";

tests/modules/services/mpd/basic-configuration.service

@@ -3,7 +3,7 @@ WantedBy=default.target
 
 [Service]
 Environment=PATH=/home/hm-user/.nix-profile/bin
-ExecStart=@mpd@/bin/mpd --no-daemon /nix/store/00000000000000000000000000000000-mpd.conf
+ExecStart=@mpd@/bin/mpd --no-daemon /nix/store/00000000000000000000000000000000-mpd.conf '--verbose'
 ExecStartPre=/nix/store/00000000000000000000000000000000-bash/bin/bash -c "/nix/store/00000000000000000000000000000000-coreutils/bin/mkdir -p '/home/hm-user/.local/share/mpd' '/home/hm-user/.local/share/mpd/playlists'"
 Type=notify
 

tests/modules/services/mpd/before-state-version-22_11.nix

@@ -3,7 +3,10 @@
 with lib;
 
 {
-  services.mpd.enable = true;
+  services.mpd = {
+    enable = true;
+    extraArgs = [ "--verbose" ];
+  };
 
   home.stateVersion = "18.09";
 

tests/modules/services/mpd/xdg-music-dir.nix

@@ -3,7 +3,11 @@
 with lib;
 
 {
-  services.mpd.enable = true;
+  services.mpd = {
+    enable = true;
+    extraArgs = [ "--verbose" ];
+  };
+
   xdg.userDirs.enable = true;
 
   home.stateVersion = "22.11";