emacs: extend startWithUserSession to start after graphical session (#3010)

modules/services/emacs.nix

@@ -81,14 +81,14 @@ in {
       enable = mkEnableOption "systemd socket activation for the Emacs service";
     };
 
-    startWithUserSession = lib.mkOption {
-      type = lib.types.bool;
+    startWithUserSession = mkOption {
+      type = with types; either bool (enum [ "graphical" ]);
       default = !cfg.socketActivation.enable;
       defaultText =
         literalExpression "!config.services.emacs.socketActivation.enable";
-      example = true;
+      example = "graphical";
       description = ''
-        Whether to launch Emacs service with the systemd user session.
+        Whether to launch Emacs service with the systemd user session.  If it is <literal>true</literal>, Emacs service is started by default.target.  If it is <literal>"graphical"</literal>, Emacs service is started by graphical-session.target.
       '';
     };
 
@@ -116,6 +116,11 @@ in {
           Documentation =
             "info:emacs man:emacs(1) https://gnu.org/software/emacs/";
 
+          After = optional (cfg.startWithUserSession == "graphical")
+            "graphical-session.target";
+          PartOf = optional (cfg.startWithUserSession == "graphical")
+            "graphical-session.target";
+
           # Avoid killing the Emacs session, which may be full of
           # unsaved buffers.
           X-RestartIfChanged = false;
@@ -156,8 +161,15 @@ in {
           ExecStopPost =
             "${pkgs.coreutils}/bin/chmod --changes +w ${socketDir}";
         };
-      } // optionalAttrs (cfg.startWithUserSession) {
-        Install = { WantedBy = [ "default.target" ]; };
+      } // optionalAttrs (cfg.startWithUserSession != false) {
+        Install = {
+          WantedBy = [
+            (if cfg.startWithUserSession == true then
+              "default.target"
+            else
+              "graphical-session.target")
+          ];
+        };
       };
 
       home = {

tests/modules/services/emacs/default.nix

@@ -1,6 +1,8 @@
 {
   emacs-service-27 = ./emacs-service-27.nix;
   emacs-service-28 = ./emacs-service-28.nix;
+  emacs-service-28-after-graphical-session-target =
+    ./emacs-service-28-after-graphical-session-target.nix;
   emacs-socket-27 = ./emacs-socket-27.nix;
   emacs-socket-28 = ./emacs-socket-28.nix;
   emacs-default-editor = ./emacs-default-editor.nix;

tests/modules/services/emacs/emacs-service-28-after-graphical-session-target.nix

@@ -0,0 +1,40 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+{
+  config = {
+    nixpkgs.overlays = [
+      (self: super: rec {
+        emacs = pkgs.writeShellScriptBin "dummy-emacs-28.2" "" // {
+          outPath = "@emacs@";
+        };
+        emacsPackagesFor = _:
+          makeScope super.newScope (_: { emacsWithPackages = _: emacs; });
+      })
+    ];
+
+    programs.emacs.enable = true;
+    services.emacs.enable = true;
+    services.emacs.client.enable = true;
+    services.emacs.extraOptions = [ "-f" "exwm-enable" ];
+    services.emacs.startWithUserSession = "graphical";
+
+    nmt.script = ''
+      assertPathNotExists home-files/.config/systemd/user/emacs.socket
+      assertFileExists home-files/.config/systemd/user/emacs.service
+      assertFileExists home-path/share/applications/emacsclient.desktop
+
+      assertFileContent home-files/.config/systemd/user/emacs.service \
+                        ${
+                          pkgs.substituteAll {
+                            inherit (pkgs) runtimeShell;
+                            src =
+                              ./emacs-service-emacs-after-graphical-session-target.service;
+                          }
+                        }
+      assertFileContent home-path/share/applications/emacsclient.desktop \
+                        ${./emacs-28-emacsclient.desktop}
+    '';
+  };
+}

tests/modules/services/emacs/emacs-service-emacs-after-graphical-session-target.service

@@ -0,0 +1,15 @@
+[Install]
+WantedBy=graphical-session.target
+
+[Service]
+ExecStart=@runtimeShell@ -l -c "@emacs@/bin/emacs --fg-daemon '-f' 'exwm-enable'"
+Restart=on-failure
+SuccessExitStatus=15
+Type=notify
+
+[Unit]
+After=graphical-session.target
+Description=Emacs text editor
+Documentation=info:emacs man:emacs(1) https://gnu.org/software/emacs/
+PartOf=graphical-session.target
+X-RestartIfChanged=false