Running into issues with chmod in my container registry module system.

container-module.nix

{ config, lib, pkgs, ... }:

with lib;
let
#   makeFiles = files:
#     let
#       files' = filter (f: f.enable) (attrValues files);
#     in pkgs.stdenvNoCC.mkDerivation {
#       name = "etc";
# 
#       builder = ./make-files.sh;
# 
#       preferLocalBuild = true;
#       allowSubstitutes = false;
# 
#       sources = map (x: x.source) files';
#       targets = map (x: x.target) files';
#       modes = map (x: x.mode) files';
#       isDirectory = map (x: if x.isDirectory then "1" else "0" ) files';
#   };
# 
  file-submodule = { name, config, ... }:
  {
    options = {
      enable = mkOption {
        type = types.bool;
        default = true;
        example = "true";
      };

      source = mkOption {
        type = types.nullOr types.path;
        default = null;
      };

      target = mkOption {
        type = types.str;
      };

      text = mkOption {
        type = types.lines;
        default = "";
      };

      mode = mkOption {
        type = types.str;
        example = "744";
        default = "744";
      };
    };

    config = {
      target = mkDefault "${name}";
      source = mkIf (config.text != "") (
        let name' = "file-" + baseNameOf name;
        in mkDefault (pkgs.writeText name' config.text));
    };
  };
in {
  options = {
    name = mkOption {
      type = types.str;
      example = "redis";
      description = "Image name";
    };

    tag = mkOption {
      type = types.str;
      default = "latest";
      example = "latest";
      description = "Image tag.";
    };

    file = mkOption {
      default = {};
      example = {};
      type = with types; loaOf (submodule [ file-submodule ]);
      description = "Extra files to place inside the image, relative to /.";
    };
  };
}

container-registry.nix

{ lib
, pkgs
, jq
, dockerTools
}:

let
  getConfig = module: (lib.evalModules {
      modules = [ module ./container-module.nix ];
      specialArgs = { inherit pkgs; };
    }).config;

  sanitize = file: file // {
    target = lib.removePrefix "/" file.target;
  };

  makeExtraFiles = { name, file }: pkgs.stdenvNoCC.mkDerivation {
    name = "extra-files";

    builder = ./make-files.sh;
    buildInputs = [ jq ];

    preferLocalBuild = true;
    allowSubstitutes = false;

    fileConfig = builtins.toJSON (map sanitize (builtins.attrValues file));
  };

  extraFiles = path:
  let
    config = getConfig path;
  in makeExtraFiles {
    inherit (config) name file;
  };
in extraFiles ./example-module.nix
#in {
#  buildModularImage = { module }:
#  let
#    config = getConfig module;
#    in dockerTools.buildLayeredImage {
#      inherit (config) name tag;
#      extraCommands = ''
#      '';
#  };
#}

example-module.nix

{ config, ... }:
{
  config = {
    name = "foo";
    file."/etc/nsswitch.conf".text =  ''
        hosts: files dns
    '';

    file."/data".mode = "777";
    file."/tmp".mode = "777";
  };
}

make-files.sh

source $stdenv/setup

mkdir -p $out

set +v
set +x
# Create directories:
echo $out
echo HELLO
echo $fileConfig | jq '.[] | select(.source == null) | "'${out}'/\(.target)"' | xargs -r mkdir -p
echo $fileConfig | jq '.[] | select(.source == null) | "'${out}'/\(.target)"' | xargs -r echo mkdir -p
echo $fileConfig | jq '.[] | select(.source == null) | "\(.mode) '${out}'/\(.target)"' | tr -d \" | xargs -r chmod -R

# Copy files:
mapfile -t cmds < <(echo $fileConfig | jq '.[] | select(.source != null) | "\(.mode) \(.source) \(.target)"' | tr -d \")
for ((k = 0; k < ${#cmds[@]}; k++)); do
  args=(${cmds[k]})
  mkdir -p $out/$(dirname ${args[2]})
  cp ${args[1]} $out/${args[2]}
  chmod ${args[0]} $out/${args[2]}
done