nixos/xsession: use graphical systemd user target

While systemd suggests using the pre-defined graphical-session user
target, I found that this interface is difficult to use. Additionally,
no other major distribution, even in their unstable versions, currently
use this mechanism.

The window or desktop manager is supposed to run in a systemd user service
which activates graphical-session.target and the user services that are
binding to this target. The issue is that we can't elegantly pass the
xsession environment to the window manager session, in particular
whereas the PassEnvironment option does work for DISPLAY, it for some
mysterious reason won't for PATH.

This commit implements a new graphical user target that works just like
default.target. Services which should be run in a graphical session just
need to declare wantedBy graphical.target. The graphical target will be
activated in the xsession before executing the window or display manager.

Fixes #17858.

10 files changed, 35 insertions, 25 deletions

diff --git a/nixos/modules/config/pulseaudio.nix b/nixos/modules/config/pulseaudio.nix
index bf66994b5022..bd80c8113483 100644
--- a/nixos/modules/config/pulseaudio.nix
+++ b/nixos/modules/config/pulseaudio.nix
@@ -240,11 +240,14 @@ in {
       };
       systemd.user = {
         services.pulseaudio = {
+          restartIfChanged = true;
           serviceConfig = {
             RestartSec = "500ms";
+            PassEnvironment = "DISPLAY";
           };
-          environment = { DISPLAY = ":${toString config.services.xserver.display}"; };
-          restartIfChanged = true;
+        };
+        sockets.pulseaudio = {
+          wantedBy = [ "sockets.target" ];
         };
       };
     })
diff --git a/nixos/modules/programs/ssh.nix b/nixos/modules/programs/ssh.nix
index a00fc0dfd19d..4faef2c609bc 100644
--- a/nixos/modules/programs/ssh.nix
+++ b/nixos/modules/programs/ssh.nix
@@ -199,9 +199,8 @@ in
     environment.etc."ssh/ssh_known_hosts".text = knownHostsText;
 
     # FIXME: this should really be socket-activated for über-awesomeness.
-    systemd.user.services.ssh-agent =
-      { enable = cfg.startAgent;
-        description = "SSH Agent";
+    systemd.user.services.ssh-agent = mkIf cfg.startAgent
+      { description = "SSH Agent";
         wantedBy = [ "default.target" ];
         serviceConfig =
           { ExecStartPre = "${pkgs.coreutils}/bin/rm -f %t/ssh-agent";
diff --git a/nixos/modules/services/monitoring/arbtt.nix b/nixos/modules/services/monitoring/arbtt.nix
index a8d5e3b7fa07..b41a3c7b5016 100644
--- a/nixos/modules/services/monitoring/arbtt.nix
+++ b/nixos/modules/services/monitoring/arbtt.nix
@@ -48,7 +48,8 @@ in {
   config = mkIf cfg.enable {
     systemd.user.services.arbtt = {
       description = "arbtt statistics capture service";
-      wantedBy = [ "default.target" ];
+      wantedBy = [ "graphical-session.target" ];
+      partOf = [ "graphical-session.target" ];
 
       serviceConfig = {
         Type = "simple";
diff --git a/nixos/modules/services/x11/compton.nix b/nixos/modules/services/x11/compton.nix
index d75d24830f8d..56bc66b71796 100644
--- a/nixos/modules/services/x11/compton.nix
+++ b/nixos/modules/services/x11/compton.nix
@@ -208,13 +208,13 @@ in {
   config = mkIf cfg.enable {
     systemd.user.services.compton = {
       description = "Compton composite manager";
-      wantedBy = [ "default.target" ];
+      wantedBy = [ "graphical-session.target" ];
+      partOf = [ "graphical-session.target" ];
       serviceConfig = {
         ExecStart = "${cfg.package}/bin/compton --config ${configFile}";
         RestartSec = 3;
         Restart = "always";
       };
-      environment.DISPLAY = ":0";
     };
 
     environment.systemPackages = [ cfg.package ];
diff --git a/nixos/modules/services/x11/display-managers/default.nix b/nixos/modules/services/x11/display-managers/default.nix
index cf6efb7dae79..58773685ec1f 100644
--- a/nixos/modules/services/x11/display-managers/default.nix
+++ b/nixos/modules/services/x11/display-managers/default.nix
@@ -122,6 +122,9 @@ let
           source ~/.xprofile
       fi
 
+      # Start systemd user services for graphical sessions
+      ${config.systemd.package}/bin/systemctl --user start graphical-session.target
+
       # Allow the user to setup a custom session type.
       if test -x ~/.xsession; then
           exec ~/.xsession
@@ -164,6 +167,9 @@ let
       ''}
 
       test -n "$waitPID" && wait "$waitPID"
+
+      ${config.systemd.package}/bin/systemctl --user stop graphical-session.target
+
       exit 0
     '';
 
@@ -325,6 +331,13 @@ in
 
   config = {
     services.xserver.displayManager.xserverBin = "${xorg.xorgserver.out}/bin/X";
+
+    systemd.user.targets.graphical-session = {
+      unitConfig = {
+        RefuseManualStart = false;
+        StopWhenUnneeded = false;
+      };
+    };
   };
 
   imports = [
diff --git a/nixos/modules/services/x11/redshift.nix b/nixos/modules/services/x11/redshift.nix
index eb5dfdf95849..992709ed0000 100644
--- a/nixos/modules/services/x11/redshift.nix
+++ b/nixos/modules/services/x11/redshift.nix
@@ -95,7 +95,8 @@ in {
   config = mkIf cfg.enable {
     systemd.user.services.redshift = {
       description = "Redshift colour temperature adjuster";
-      wantedBy = [ "default.target" ];
+      wantedBy = [ "graphical-session.target" ];
+      partOf = [ "graphical-session.target" ];
       serviceConfig = {
         ExecStart = ''
           ${cfg.package}/bin/redshift \
@@ -107,12 +108,6 @@ in {
         RestartSec = 3;
         Restart = "always";
       };
-      environment = {
-        DISPLAY = ":${toString (
-          let display = config.services.xserver.display;
-          in if display != null then display else 0
-        )}";
-      };
     };
   };
 
diff --git a/nixos/modules/services/x11/unclutter-xfixes.nix b/nixos/modules/services/x11/unclutter-xfixes.nix
index b94dfb1a26a6..71262431b685 100644
--- a/nixos/modules/services/x11/unclutter-xfixes.nix
+++ b/nixos/modules/services/x11/unclutter-xfixes.nix
@@ -43,7 +43,8 @@ in {
   config = mkIf cfg.enable {
     systemd.user.services.unclutter-xfixes = {
       description = "unclutter-xfixes";
-      wantedBy = [ "graphical.target" ];
+      wantedBy = [ "graphical-session.target" ];
+      partOf = [ "graphical-session.target" ];
       serviceConfig.ExecStart = ''
         ${cfg.package}/bin/unclutter \
           --timeout ${toString cfg.timeout} \
diff --git a/nixos/modules/services/x11/unclutter.nix b/nixos/modules/services/x11/unclutter.nix
index a22e5ac2c95a..5f16a680050d 100644
--- a/nixos/modules/services/x11/unclutter.nix
+++ b/nixos/modules/services/x11/unclutter.nix
@@ -56,19 +56,17 @@ in {
   config = mkIf cfg.enable {
     systemd.user.services.unclutter = {
       description = "unclutter";
-      wantedBy = [ "default.target" ];
+      wantedBy = [ "graphical-session.target" ];
+      partOf = [ "graphical-session.target" ];
       serviceConfig.ExecStart = ''
         ${cfg.package}/bin/unclutter \
           -idle ${toString cfg.timeout} \
-          -display :${toString (
-             let display = config.services.xserver.display;
-             in if display != null then display else 0
-          )} \
           -jitter ${toString (cfg.threeshold - 1)} \
           ${optionalString cfg.keystroke "-keystroke"} \
           ${concatMapStrings (x: " -"+x) cfg.extraOptions} \
           -not ${concatStringsSep " " cfg.excluded} \
       '';
+      serviceConfig.PassEnvironment = "DISPLAY";
       serviceConfig.RestartSec = 3;
       serviceConfig.Restart = "always";
     };
diff --git a/nixos/modules/services/x11/urxvtd.nix b/nixos/modules/services/x11/urxvtd.nix
index 57ad93f20174..f2ce089ce19a 100644
--- a/nixos/modules/services/x11/urxvtd.nix
+++ b/nixos/modules/services/x11/urxvtd.nix
@@ -21,9 +21,8 @@ in {
     systemd.user = {
       sockets.urxvtd = {
         description = "socket for urxvtd, the urxvt terminal daemon";
-        after = [ "graphical.target" ];
-        wants = [ "graphical.target" ];
-        wantedBy = [ "sockets.target" ];
+        wantedBy = [ "graphical-session.target" ];
+        partOf = [ "graphical-session.target" ];
         socketConfig = {
           ListenStream = "%t/urxvtd-socket";
         };
diff --git a/nixos/modules/services/x11/xbanish.nix b/nixos/modules/services/x11/xbanish.nix
index e1e3cbc8e441..b95fac68f165 100644
--- a/nixos/modules/services/x11/xbanish.nix
+++ b/nixos/modules/services/x11/xbanish.nix
@@ -20,7 +20,8 @@ in {
   config = mkIf cfg.enable {
     systemd.user.services.xbanish = {
       description = "xbanish hides the mouse pointer";
-      wantedBy = [ "default.target" ];
+      wantedBy = [ "graphical-session.target" ];
+      partOf = [ "graphical-session.target" ];
       serviceConfig.ExecStart = ''
         ${pkgs.xbanish}/bin/xbanish ${cfg.arguments}
       '';