fixup! Update nix-shell for Haskell.nix changes

nix/build-tools-overlay.nix

@@ -56,14 +56,11 @@ pkgs: super: let
   # A script for updating materialized files
   regenerateMaterialized = pkgs.writeShellScriptBin "regenerate-materialized-nix"
     (pkgs.lib.optionalString enableMaterialization
-      (pkgs.lib.concatStringsSep "\n" (pkgs.lib.mapAttrsToList (name: tool: ''
-        printf '\n\n\n*** Updating materialized nix for ${name} ***\n\n'
-        ${mkMaterialize name tool}
-      '') tools)));
-  mkMaterialize = name: args: let
-    plan = (mkTool name (args // { checkMaterialization = true; })).project.plan-nix;
-  in
-    plan.generateMaterialized or "echo fixme";
+      (pkgs.lib.concatStringsSep "\n" (pkgs.lib.mapAttrsToList (name: hsPkg: ''
+        echo 'Updating materialized nix for ${name}'
+        ${mkMaterialize hsPkg}
+      '') hsPkgs)));
+  mkMaterialize = hsPkg: hsPkg.project.plan-nix.passthru.updateMaterialized;
   # https://github.com/input-output-hk/nix-tools/issues/97
   enableMaterialization = pkgs.stdenv.isLinux;