daemon: Rely on systemd unit file for X11 plugin initialization

For GNOME X11 sessions, avoid relying on xdg autostart desktop files
to initialize the X11 plugins. This is now handled via a systemd unit
file.

The xdg autostart is still installed, but has been made to instruct
GNOME to skip it with X-GNOME-HiddenUnderSystemd. This is still the
primary way to initialize X11 plugins for other DEs.

Part-of: <https://gitlab.freedesktop.org/pulseaudio/pulseaudio/-/merge_requests/467>

src/daemon/meson.build

@@ -152,6 +152,8 @@ endif
 if systemd_dep.found()
   sd_user_service_conf = configuration_data()
   sd_user_service_conf.set('PA_BINARY', cdata.get_unquoted('PA_BINARY'))
+  sd_user_service_conf.set('PACTL_BINARY', join_paths(bindir, 'pactl'))
+  sd_user_service_conf.set('PA_X11_BINARY', join_paths(bindir, 'start-pulseaudio-x11'))
 
   sd_user_service_file = configure_file(
     input : 'systemd/user/pulseaudio.service.in',
@@ -161,6 +163,14 @@ if systemd_dep.found()
     install_dir : systemduserunitdir,
   )
 
+  sd_user_x11_service_file = configure_file(
+    input : 'systemd/user/pulseaudio-x11.service.in',
+    output : 'pulseaudio-x11.service',
+    configuration : sd_user_service_conf,
+    install : true,
+    install_dir : systemduserunitdir,
+  )
+
   install_data('systemd/user/pulseaudio.socket',
     install_dir: systemduserunitdir,
   )

src/daemon/pulseaudio.desktop.in

@@ -6,4 +6,5 @@ Exec=start-pulseaudio-x11
 Terminal=false
 Type=Application
 X-GNOME-Autostart-Phase=Initialization
+X-GNOME-HiddenUnderSystemd=true
 X-KDE-autostart-phase=1

src/daemon/systemd/user/pulseaudio-x11.service.in

@@ -0,0 +1,18 @@
+[Unit]
+Description=Sound Service (X11 Plugins)
+Requires=pulseaudio.service
+After=pulseaudio.service
+ConditionUser=!root
+PartOf=gnome-session-x11.target
+
+[Service]
+ExecStart=@PA_X11_BINARY@
+ExecStop=@PA_X11_BINARY@ stop
+LockPersonality=yes
+MemoryDenyWriteExecute=yes
+NoNewPrivileges=yes
+RestrictNamespaces=yes
+SystemCallArchitectures=native
+SystemCallFilter=@system-service
+Type=simple
+UMask=0077