Merge pull request #45784 from oxij/pull/44720-shell-env-edited

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

nixos/modules/config/shells-environment.nix

@@ -163,15 +163,24 @@ in
         /bin/sh
       '';
 
+    # For resetting environment with `. /etc/set-environment` when needed
+    # and discoverability (see motivation of #30418).
+    environment.etc."set-environment".source = config.system.build.setEnvironment;
+
     system.build.setEnvironment = pkgs.writeText "set-environment"
-       ''
-         ${exportedEnvVars}
+      ''
+        # DO NOT EDIT -- this file has been generated automatically.
 
-         ${cfg.extraInit}
+        # Prevent this file from being sourced by child shells.
+        export __NIXOS_SET_ENVIRONMENT_DONE=1
 
-         # ~/bin if it exists overrides other bin directories.
-         export PATH="$HOME/bin:$PATH"
-       '';
+        ${exportedEnvVars}
+
+        ${cfg.extraInit}
+
+        # ~/bin if it exists overrides other bin directories.
+        export PATH="$HOME/bin:$PATH"
+      '';
 
     system.activationScripts.binsh = stringAfter [ "stdio" ]
       ''