moonbit-overlay

Binary distributed MoonBit toolchains.

NOTE: moonbit-compiler was already open sourced, BUT only wasm-gc backend is available. Considering this is an incomplete compiler and the version is quite lagging, this project will still only be able to use patched pre-built binaries for a long time.

Quick Start

Run moon in one line

nix run github:moonbit-community/moonbit-overlay#moon

List all available binaries

nix run github:moonbit-community/moonbit-overlay#<tab>

Create devshell from template

nix flake init -t github:moonbit-community/moonbit-overlay

Features

• build from source in future.
• versioning!
• patchelf works :)

Example

flake with overlay

{
  description = "A startup basic MoonBit project";

  inputs = {
    flake-parts.url = "github:hercules-ci/flake-parts";
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

    devshell.url = "github:numtide/devshell";
    moonbit-overlay.url = "github:moonbit-community/moonbit-overlay";
  };

  outputs = inputs@{ flake-parts, ... }:
    flake-parts.lib.mkFlake { inherit inputs; } {
      imports = [
        inputs.devshell.flakeModule
      ];

      perSystem = { inputs', system, pkgs, ... }: {
        _module.args.pkgs = import inputs.nixpkgs {
          inherit system;
          overlays = [ inputs.moonbit-overlay.overlays.default ];
        };

        devshells.default = {
            packages = with pkgs; [
              moonbit-bin.moonbit.latest
            ];
          };
      };

      systems = [
        "x86_64-linux"
        "aarch64-darwin"
        "x86_64-darwin"
      ];
    };
}

Moonbit Package Builder

buildMoonPackage builds a MoonBit project from source inside the Nix sandbox. It reads moon.mod.json to auto-detect version, preferred target, and source directory — minimal configuration is needed:

{
  description = "A startup basic MoonBit project";

  inputs = {
    flake-parts.url = "github:hercules-ci/flake-parts";
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";

    moonbit-overlay.url = "github:moonbit-community/moonbit-overlay";
    moon-registry = {
      url = "git+https://mooncakes.io/git/index";
      flake = false;
    };
  };

  outputs = inputs@{ flake-parts, ... }:
    flake-parts.lib.mkFlake { inherit inputs; } {

      perSystem = { inputs', system, pkgs, ... }: {
        _module.args.pkgs = import inputs.nixpkgs {
          inherit system;
          overlays = [ inputs.moonbit-overlay.overlays.default ];
        };

        packages.default = pkgs.moonPlatform.buildMoonPackage {
          src = ./.;
          moonModJson = ./moon.mod.json;
          moonRegistryIndex = inputs.moon-registry;
        };
      };

      systems = [
        "x86_64-linux"
        "aarch64-darwin"
        "x86_64-darwin"
      ];
    };
}

What it does automatically

• Resolves and caches all transitive dependencies from mooncakes.io registry
• Reads version, preferred-target, and source from moon.mod.json
• Builds with moon build --target <preferred-target> --release
• Installs all produced binaries to $out/bin/

Optional parameters

Parameter	Default	Description
name	from moon.mod.json	Derivation name (last component of mod name)
version	from moon.mod.json	Package version
moonTarget	preferred-target in moon.mod.json	Build target (native, js, wasm, etc.)
moonFlags	[]	Extra flags passed to moon build
buildPhase	auto-generated	Override the build phase
installPhase	auto-generated	Override the install phase
nativeBuildInputs	[]	Merged with moonbit toolchain

Public API

moonPlatform exposes three functions:

• buildMoonPackage — high-level builder (shown above)
• buildCachedRegistry — fetch and cache mooncakes.io dependencies
• bundleWithRegistry — create a complete MOON_HOME with toolchain + core + registry

Bundled MoonBit Toolchains

moonbit-bin.moonbit.latest

MoonBit LSP (distributed with compiler)

The moonbit-bin.moonbit.${version} package already includes moonbit-lsp.

moonbit-bin.moonbit.latest

Version

latest

moonbit-bin.moonbit.latest

nightly

moonbit-bin.moonbit.nightly

nightly is a rolling channel that tracks the upstream nightly build (the same one the official installer fetches with install.sh nightly).

specific version

moonbit-bin.moonbit.v0_1_20241031-7204facb6

Check available versions in the directory.

The original version of MoonBit is written as v0.1.20241031+7204facb6, for convenience, we escape it to format like v0_1_20241031-7204facb6.

legacyPackages & packages

The overlay now provides both legacyPackages and packages attributes:

• legacyPackages: This is the original, structured attribute set. Packages are grouped by type (e.g., moonbit, cli, core) and version, making it easier to navigate the package hierarchy.
• packages: This is a flattened attribute set, where each package is exposed as a single attribute (e.g., moonbit_latest, cli_v0_1_20241031-7204facb6). This structure is required for nix flake check to work correctly, as it expects all packages to be directly accessible under the packages attribute.

Both are provided to maintain compatibility and usability: use legacyPackages for structured access, and packages for flake checks and direct access.

Some deprecated packages are still exposed for compatibility; attempting to use them will show a warning and prevent building.

TODO

• overridable
• build from source (core) see pull#10
• re-support legacy default.nix

Inspiration

The moonbit-overlay is heavily inspired by rust-overlay.

License

This project is licensed under the MIT License. See the LICENSE file for details.