emacs: Fix socket activation

modules/services/emacs.nix

@@ -205,9 +205,21 @@ in {
           FileDescriptorName = "server";
           SocketMode = "0600";
           DirectoryMode = "0700";
+          # This prevents the service from immediately starting again
+          # after being stopped, due to the function
+          # `server-force-stop' present in `kill-emacs-hook', which
+          # calls `server-running-p', which opens the socket file.
+          FlushPending = true;
         };
 
-        Install = { WantedBy = [ "sockets.target" ]; };
+        Install = {
+          WantedBy = [ "sockets.target" ];
+          # Adding this Requires= dependency ensures that systemd
+          # manages the socket file, in the case where the service is
+          # started when the socket is stopped.
+          # The socket unit is implicitly ordered before the service.
+          RequiredBy = [ "emacs.service" ];
+        };
       };
     })
   ]);

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

@@ -1,9 +1,11 @@
 [Install]
+RequiredBy=emacs.service
 WantedBy=sockets.target
 
 [Socket]
 DirectoryMode=0700
 FileDescriptorName=server
+FlushPending=true
 ListenStream=%t/emacs/server
 SocketMode=0600