emacs: fix service environment

Emacs populates 'exec-path' at launch from the 'PATH' environment
variable. Likewise, the emacs derivation from nixpkgs populates
'load-path' from the 'NIX_PROFILES' variable. As neither of these are
available by default in the systemd user manager, revert to the
previous behavior of launching the Emacs daemon from a login shell.

Fixes #1354
Fixes #1340
PR #1355

modules/services/emacs.nix

@@ -97,13 +97,19 @@ in {
         };
 
         Service = {
-          ExecStart = "${emacsBinPath}/emacs --fg-daemon${
+          # We wrap ExecStart in a login shell so Emacs starts with the user's
+          # environment, most importantly $PATH and $NIX_PROFILES. It may be
+          # worth investigating a more targeted approach for user services to
+          # import the user environment.
+          ExecStart = ''
+            ${pkgs.runtimeShell} -l -c "${emacsBinPath}/emacs --fg-daemon${
             # In case the user sets 'server-directory' or 'server-name' in
             # their Emacs config, we want to specify the socket path explicitly
             # so launching 'emacs.service' manually doesn't break emacsclient
             # when using socket activation.
-              optionalString cfg.socketActivation.enable ''="${socketPath}"''
+              optionalString cfg.socketActivation.enable
-            }";
+              "=${escapeShellArg socketPath}"
+            }"'';
           # We use '(kill-emacs 0)' to avoid exiting with a failure code, which
           # would restart the service immediately.
           ExecStop = "${emacsBinPath}/emacsclient --eval '(kill-emacs 0)'";

tests/modules/services/emacs/emacs-service-emacs.service

@@ -2,7 +2,7 @@
 WantedBy=default.target
 
 [Service]
-ExecStart=@emacs@/bin/emacs --fg-daemon
+ExecStart=@runtimeShell@ -l -c "@emacs@/bin/emacs --fg-daemon"
 ExecStop=@emacs@/bin/emacsclient --eval '(kill-emacs 0)'
 Restart=on-failure
 

tests/modules/services/emacs/emacs-service.nix

@@ -24,7 +24,12 @@ with lib;
       assertFileExists home-path/share/applications/emacsclient.desktop
 
       assertFileContent home-files/.config/systemd/user/emacs.service \
-                        ${./emacs-service-emacs.service}
+                        ${
+                          pkgs.substituteAll {
+                            inherit (pkgs) runtimeShell;
+                            src = ./emacs-service-emacs.service;
+                          }
+                        }
       assertFileContent home-path/share/applications/emacsclient.desktop \
                         ${./emacs-emacsclient.desktop}
     '';

tests/modules/services/emacs/emacs-socket-26-emacs.service

@@ -1,5 +1,5 @@
 [Service]
-ExecStart=@emacs@/bin/emacs --fg-daemon="%T/emacs%U/server"
+ExecStart=@runtimeShell@ -l -c "@emacs@/bin/emacs --fg-daemon='%T/emacs%U/server'"
 ExecStop=@emacs@/bin/emacsclient --eval '(kill-emacs 0)'
 Restart=on-failure
 

tests/modules/services/emacs/emacs-socket-26.nix

@@ -27,7 +27,12 @@ with lib;
       assertFileContent home-files/.config/systemd/user/emacs.socket \
                         ${./emacs-socket-26-emacs.socket}
       assertFileContent home-files/.config/systemd/user/emacs.service \
-                        ${./emacs-socket-26-emacs.service}
+                        ${
+                          pkgs.substituteAll {
+                            inherit (pkgs) runtimeShell;
+                            src = ./emacs-socket-26-emacs.service;
+                          }
+                        }
       assertFileContent home-path/share/applications/emacsclient.desktop \
                         ${./emacs-emacsclient.desktop}
     '';

tests/modules/services/emacs/emacs-socket-27-emacs.service

@@ -1,5 +1,5 @@
 [Service]
-ExecStart=@emacs@/bin/emacs --fg-daemon="%t/emacs/server"
+ExecStart=@runtimeShell@ -l -c "@emacs@/bin/emacs --fg-daemon='%t/emacs/server'"
 ExecStop=@emacs@/bin/emacsclient --eval '(kill-emacs 0)'
 Restart=on-failure
 

tests/modules/services/emacs/emacs-socket-27.nix

@@ -29,7 +29,12 @@ in {
       assertFileContent home-files/.config/systemd/user/emacs.socket \
                         ${./emacs-socket-27-emacs.socket}
       assertFileContent home-files/.config/systemd/user/emacs.service \
-                        ${./emacs-socket-27-emacs.service}
+                        ${
+                          pkgs.substituteAll {
+                            inherit (pkgs) runtimeShell;
+                            src = ./emacs-socket-27-emacs.service;
+                          }
+                        }
       assertFileContent home-path/share/applications/emacsclient.desktop \
                         ${./emacs-emacsclient.desktop}
     '';