Added an error message when using enableFakechroot on Darwin (#327336)

* Added an error message when using enableFakechroot on Darwin

Co-authored-by: Valentin Gagarin <valentin@gagarin.work>

pkgs/build-support/docker/default.nix

@@ -24,6 +24,7 @@
 , runtimeShell
 , shadow
 , skopeo
+, stdenv
 , storeDir ? builtins.storeDir
 , substituteAll
 , symlinkJoin
@@ -922,6 +923,13 @@ rec {
       assert
       (lib.assertMsg (maxLayers > 1)
         "the maxLayers argument of dockerTools.buildLayeredImage function must be greather than 1 (current value: ${toString maxLayers})");
+      assert
+      (lib.assertMsg (enableFakechroot -> !stdenv.isDarwin) ''
+        cannot use `enableFakechroot` because `proot` is not portable to Darwin. Workarounds:
+              - use `fakeRootCommands` with the restricted `fakeroot` environment
+              - cross-compile your packages
+              - run your packages in a virtual machine
+              Discussion: https://github.com/NixOS/nixpkgs/issues/327311'');
       let
         baseName = baseNameOf name;