Emacs should only be the default editor if it is installed.

config/etc.nix

@@ -12,7 +12,6 @@ with lib;
   };
 
   environment.variables = mkIf (elem "etcvars" config.machine.conffiles) {
-    EDITOR="emacsclient -ca nano";
     NIXPKGS_ALLOW_UNFREE="1";
     WINEDLLOVERRIDES="winemenubuilder.exe=d";
     LC_CTYPE="zh_CN.UTF-8";

pkgs/pkgsets.nix

@@ -286,9 +286,10 @@ in {
                             ++ (optPkgs uniProgs "uniProgs")
                             ++ (optPkgs xpkgs "xpkgs");
 
-  services.emacs = {
-    enable = (elem "emacs" cfg.pkgs);
-    install = (elem "emacs" cfg.pkgs);
+  services.emacs = mkIf (elem "emacs" cfg.pkgs) {
+    defaultEditor = true;
+    enable = true;
+    install = true;
     package = emacs;
   };
 }