Cross compilation with Elixir and Nim NIFs

compile.nim_nif.ex

# lib/mix/tasks/compile.nim_nif.ex

defmodule Mix.Tasks.Compile.NimNif do
  use Mix.Task.Compiler

  @bindings_dir Path.join(["lib", "native", "bindings"])
  @generated_dir Path.join(@bindings_dir, "generated")
  @hash_file Path.join(@generated_dir, ".nif_hash")

  defp ensure_directories_exist() do
    File.mkdir_p!(@bindings_dir)
    File.mkdir_p!(@generated_dir)
  end

  defp files_changed?() do
    current_hash = compute_total_hash()
    previous_hash = read_previous_hash()
    current_hash != previous_hash
  end

  defp compute_total_hash() do
    @generated_dir
    |> File.ls!()
    |> Enum.reject(&(&1 == ".nif_hash"))
    |> Enum.sort()
    |> Enum.map(&compute_file_hash(Path.join(@generated_dir, &1)))
    |> Enum.join()
    |> :erlang.md5()
    |> Base.encode16(case: :lower)
  end

  defp compute_file_hash(file_path) do
    file_path
    |> File.read!()
    |> :erlang.md5()
    |> Base.encode16(case: :lower)
  end

  defp read_previous_hash() do
    case File.read(@hash_file) do
      {:ok, hash} -> hash
      {:error, _} -> ""
    end
  end

  defp write_current_hash() do
    hash = compute_total_hash()
    File.write!(@hash_file, hash)
  end

  def run(_args) do
    ensure_directories_exist()

    if files_changed?() do
      compile_nif()
      write_current_hash()
      :ok
    else
      :noop
    end
  end

  defp compile_nif() do
    # Remove only .ex files in the bindings/generated directory
    if File.dir?(@generated_dir) do
      @generated_dir
      |> File.ls!()
      |> Enum.filter(&String.ends_with?(&1, ".ex"))
      |> Enum.each(fn file ->
        File.rm!(Path.join(@generated_dir, file))
      end)
    end

    # Generate the nimble bindings
    {result, _error_code} =
      System.cmd("nimble", ["bindings"], cd: "lib/native", stderr_to_stdout: true)

    Mix.shell().info(result)

    # Run mix format on the generated files
    {result, _error_code} =
      System.cmd("mix", ["format", "lib/native/bindings/generated/*.ex"], stderr_to_stdout: true)

    Mix.shell().info(result)
  end
end

mix.exs

defmodule NimlerElixir.MixProject do
  use Mix.Project

  def project do
    [
      app: :nimler_elixir,
      version: "0.1.0",
      elixir: "~> 1.17",
      start_permanent: Mix.env() == :prod,
      compilers: [:nim_nif] ++ Mix.compilers(),
      deps: deps()
    ]
  end

  # Run "mix help compile.app" to learn about applications.
  def application do
    [
      extra_applications: [:logger]
    ]
  end

  # Run "mix help deps" to learn about dependencies.
  defp deps do
    []
  end
end

nif.nimble

# lib/native/nif.nimble

# Package
version       = "0.1.0"
author        = "Tom"
description   = "A Nimble library for generating bindings using Nimler."
license       = "MIT"

# Dependencies
requires "nim >= 1.14.0"

# Tasks
import os, strutils

task bindings, "Generate Bindings":
  proc compile(libName: string, flags = "") =
    let extraFlags = case hostOS
      of "macosx": "--passL:'-undefined dynamic_lookup'"
      of "windows": "--app:lib"
      else: "--passL:'-shared'"
    
    let cmd = "nim c -f " & flags & " " & extraFlags & " -d:release --app:lib --gc:orc -d:nimlerGenWrapper --out:" & libName & " --outdir:bindings/generated nif.nim"
    echo "Executing: ", cmd
    exec cmd

  let (libPrefix, libExt) = case hostOS
    of "windows": ("", ".dll")
    of "linux": ("lib", ".so")
    of "macosx": ("lib", ".dylib.so")
    else: ("lib", ".so")

  let libName = libPrefix & "nif" & libExt
  let outputName = "bindings/generated/" & libName

  case hostOS
  of "windows":
    compile(libName)
  of "linux":
    compile(libName)
  of "macosx":
    when hostCPU == "arm64":
      compile(libName, "--cpu:arm64")
    else:
      compile(libName, "--cpu:amd64")
  else:
    echo "Unsupported operating system"
    quit(1)

  if fileExists(outputName):
    echo "Library compiled: " & libName
  else:
    echo "Compilation failed: " & outputName & " not found"
    quit(1)

nim.cfg

cc:gcc
verbosity:2
app:lib
mm:orc
define:noMain
define:noSignalHandler
opt:speed
stackTrace:off
lineTrace:off
warning[GcUnsafe]:off
hint[Exec]:off
hint[Link]:off
hint[Processing]:off
hint[GcStats]:off
hint[GlobalVar]:off
nimblepath:"$home/.nimble/pkgs2/"