Unhelpful Error when Attempting to Add Non-Existent Static Directory

[portrik]

Description

I have run into this issue accidentally when trying to bundle a non-existent static directory. Instead of getting some sensible error in the vein of StaticDirNotFound or something similar, I instead got CannotCreateTempDirectory(Enoent).

The error originates at the start of do_build, maybe just mapping the errors from simplifile more granularly could solve the issue? If possible, I could take a swing at a PR.

Reproduction Steps

The code below will echo the CannotCreateTempDirectory(Enoent) error.

import gleam/io
import lustre/element/html.{html}
import lustre/ssg

const build_directory = "./dist"

pub fn main() {
  let build_result =
    ssg.new(build_directory)
    // Adding the non-existent static dir produces `CannotCreateTempDirectory(Enoent)` in the echo below
    |> ssg.add_static_dir("./does-not-exist")
    |> ssg.add_static_route(
      "/",
      html([], [html.h1([], [html.text("This will never render")])]),
    )
    |> ssg.build

  case build_result {
    Ok(_) -> io.println("Success")

    Error(error) -> {
      echo error

	  Nil
    }
  }
}