mpd: specify dependency of service on socket

This allows `systemctl --user restart mpd.socket` to work properly.

modules/services/mpd.nix

@@ -171,10 +171,17 @@ in {
     ];
 
     systemd.user.services.mpd = {
-      Unit = {
-        After = [ "network.target" "sound.target" ];
-        Description = "Music Player Daemon";
-      };
+      Unit = mkMerge [
+        {
+          Description = "Music Player Daemon";
+          After = [ "network.target" "sound.target" ];
+        }
+
+        (mkIf cfg.network.startWhenNeeded {
+          Requires = [ "mpd.socket" ];
+          After = [ "mpd.socket" ];
+        })
+      ];
 
       Install = mkIf (!cfg.network.startWhenNeeded) {
         WantedBy = [ "default.target" ];

tests/modules/services/mpd/default.nix

@@ -1,5 +1,6 @@
 {
   mpd-basic-configuration = ./basic-configuration.nix;
   mpd-before-state-version-22_11 = ./before-state-version-22_11.nix;
+  mpd-start-when-needed = ./start-when-needed.nix;
   mpd-xdg-music-dir = ./xdg-music-dir.nix;
 }

tests/modules/services/mpd/start-when-needed.nix

@@ -0,0 +1,29 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  services.mpd = {
+    enable = true;
+    musicDirectory = "/my/music/dir";
+    extraArgs = [ "--verbose" ];
+    network.startWhenNeeded = true;
+  };
+
+  home.stateVersion = "22.11";
+
+  test.stubs.mpd = { };
+
+  nmt.script = ''
+    serviceFile=$(normalizeStorePaths home-files/.config/systemd/user/mpd.service)
+    assertFileContent "$serviceFile" ${./start-when-needed.service}
+
+    socketFile=home-files/.config/systemd/user/mpd.socket
+    assertFileContent "$socketFile" ${./start-when-needed.socket}
+
+    confFile=$(grep -o \
+        '/nix/store/.*-mpd.conf' \
+        $TESTED/home-files/.config/systemd/user/mpd.service)
+    assertFileContent "$confFile" ${./basic-configuration.conf}
+  '';
+}

tests/modules/services/mpd/start-when-needed.service

@@ -0,0 +1,12 @@
+[Service]
+Environment=PATH=/home/hm-user/.nix-profile/bin
+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
+
+[Unit]
+After=network.target
+After=sound.target
+After=mpd.socket
+Description=Music Player Daemon
+Requires=mpd.socket

tests/modules/services/mpd/start-when-needed.socket

@@ -0,0 +1,8 @@
+[Install]
+WantedBy=sockets.target
+
+[Socket]
+Backlog=5
+KeepAlive=true
+ListenStream=127.0.0.1:6600
+ListenStream=%t/mpd/socket