nixos/shells: Avoid overriding the environment for other child shells

nixos/modules/config/shells-environment.nix

@@ -162,8 +162,13 @@ in
         /bin/sh
       '';
 
-    system.build.setEnvironment = pkgs.writeText "set-environment"
+    environment.etc."set-environment".text =
        ''
+         # DO NOT EDIT -- this file has been generated automatically.
+
+         # Prevent this file from being sourced by child shells.
+         export __NIXOS_SET_ENVIRONMENT_DONE=1
+
          ${exportedEnvVars}
 
          ${cfg.extraInit}

nixos/modules/programs/bash/bash.nix

@@ -126,7 +126,9 @@ in
     programs.bash = {
 
       shellInit = ''
-        ${config.system.build.setEnvironment.text}
+        if [ -z "$__NIXOS_SET_ENVIRONMENT_DONE" ]; then
+          . /etc/set-environment
+        fi
 
         ${cfge.shellInit}
       '';

nixos/modules/programs/fish.nix

@@ -109,7 +109,9 @@ in
       set fish_function_path ${pkgs.fish-foreign-env}/share/fish-foreign-env/functions $__fish_datadir/functions
 
       # source the NixOS environment config
-      fenv source ${config.system.build.setEnvironment}
+      if [ -z "$__NIXOS_SET_ENVIRONMENT_DONE" ]
+        fenv source /etc/set-environment
+      end
 
       # clear fish_function_path so that it will be correctly set when we return to $__fish_datadir/config.fish
       set -e fish_function_path

nixos/modules/programs/zsh/zsh.nix

@@ -103,7 +103,9 @@ in
         if [ -n "$__ETC_ZSHENV_SOURCED" ]; then return; fi
         export __ETC_ZSHENV_SOURCED=1
 
-        ${config.system.build.setEnvironment.text}
+        if [ -z "$__NIXOS_SET_ENVIRONMENT_DONE" ]; then
+          . /etc/set-environment
+        fi
 
         ${cfge.shellInit}
 

nixos/modules/services/editors/emacs.nix

@@ -87,7 +87,7 @@ in {
 
       serviceConfig = {
         Type      = "forking";
-        ExecStart = "${pkgs.bash}/bin/bash -c 'source ${config.system.build.setEnvironment}; exec ${cfg.package}/bin/emacs --daemon'";
+        ExecStart = "${pkgs.bash}/bin/bash -c 'source /etc/set-environment; exec ${cfg.package}/bin/emacs --daemon'";
         ExecStop  = "${cfg.package}/bin/emacsclient --eval (kill-emacs)";
         Restart   = "always";
       };