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

1 files changed, 9 insertions, 3 deletions

diff --git a/modules/services/emacs.nix b/modules/services/emacs.nix
index 70c8d0d7041..a73b750c513 100644
--- a/modules/services/emacs.nix
+++ b/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)'";