Support npm submodules

nix/default.nix

@@ -20,6 +20,8 @@
 , spagoPackages ? "${src}/spago-packages.nix"
   # Configuration that will be used to generate a `devShell` for the project
 , shell ? { }
+  # Path to submodule locations that needs to be copied when making node env
+, submodules ? [ ]
 , ...
 }:
 let
@@ -36,8 +38,15 @@ let
       } ''
       mkdir $out
       cd $out
-      cp ${packageLock} ./package-lock.json
-      cp ${packageJson} ./package.json
+      ${builtins.concatStringsSep "\n"
+        (builtins.map
+          (modulePath:
+            "cp ${modulePath} ./${builtins.baseNameOf (builtins.toString modulePath)} -r")
+          submodules
+        )
+       }
+      cp ${packageLock} ./package-lock.json -f
+      cp ${packageJson} ./package.json -f
       node2nix ${pkgs.lib.optionalString withDevDeps "--development" } \
         --lock ./package-lock.json -i ./package.json
     '')