 
   defp do_overlay(_release, output_dir, {:mkdir, path}, vars) when is_binary(path) do
     with {:ok, path} <- template_str(path, vars),
+         _           <- Logger.debug("Applying mkdir overlay for #{path}"),
          expanded    <- Path.join(output_dir, path),
          :ok         <- File.mkdir_p(expanded),
       do: {:ok, path}

  relative to the project root, but overlay output paths are relative to the root directory for the current
  release, which is why the directory is created in `rel/my_release`, and not in the project root.
  """
  alias Mix.Releases.Release

  @typep overlay :: {:mkdir, String.t} |
                    {:copy, String.t, String.t} |

    with true             <- File.exists?(tmpl_path),
         {:ok, templated} <- template_file(tmpl_path, vars),
         expanded_to      <- Path.join(output_dir, to),
         _                <- Logger.debug("Applying template overlay with #{tmpl_path} to #{to}"),
         :ok              <- File.mkdir_p(Path.dirname(expanded_to)),
         :ok              <- File.write(expanded_to, templated),
      do: {:ok, to}
