roc-overlay

A Nix flake for the Roc new-compiler nightly binaries. Inspired by Mitchell Hashimoto's zig-overlay.

This flake just mirrors prebuilt official Roc binaries; it does not build Roc from source. At present, it only provides nightly releases, as the new Zig compiler has no stable release yet.

Not using Nix? roc-lang/setup-roc is the official GitHub Action for installing Roc on CI, and it also covers Windows.

This repo was originally created by @thebrandonlucas, thanks Brandon :heart:

Usage

Quickstart from shell

# To get the latest nightly:

# Create a shell with the compiler.
nix shell github:roc-lang/roc-overlay
roc version

# Run one off commands directly from the flake.
nix run github:roc-lang/roc-overlay -- version

# For a pinned Roc release:
nix shell 'github:roc-lang/roc-overlay#nightly-2026-08-07-8d23662'

Release tags up to nightly-2026-August-05-24f0b47 spell the month out in English; from nightly-2026-08-06-61bbb59 onwards they use a two-digit month. Both forms are recorded and can be selected as shown above.

As a package in your own flake.nix

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    roc-overlay.url = "github:roc-lang/roc-overlay";
    roc-overlay.inputs.nixpkgs.follows = "nixpkgs";
  };

  outputs = {nixpkgs, roc-overlay, ...}: let
    system = "x86_64-linux";
    pkgs = nixpkgs.legacyPackages.${system};
  in {
    devShells.${system}.default = pkgs.mkShell {
      packages = [
        roc-overlay.packages.${system}.nightly
      ];
    };
  };
}

Select a historical package with roc-overlay.packages.${system}."<release-tag>".

As an overlay

{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
    roc-overlay.url = "github:roc-lang/roc-overlay";
    roc-overlay.inputs.nixpkgs.follows = "nixpkgs";
  };

  outputs = {nixpkgs, roc-overlay, ...}: let
    system = "x86_64-linux";
    pkgs = import nixpkgs {
      inherit system;
      overlays = [roc-overlay.overlays.default];
    };
  in {
    devShells.${system}.default = pkgs.mkShell {
      packages = [
        pkgs.rocpkgs.nightly
      ];
    };
  };
}

Updating

The consumer's flake.lock pins the selected overlay commit, so Roc updates are explicit:

nix flake update roc-overlay

Supported systems

• x86_64-linux
• aarch64-linux
• x86_64-darwin
• aarch64-darwin

Intel macOS packages use the last compatible Nixpkgs Darwin release branch (Nixpkgs 26.05) because current unstable Nixpkgs has dropped that system.

default and nightly point to the newest release in sources.json. Every recorded release also remains available under its complete release tag.

On Linux, roc is wrapped with Nix's C toolchain and core utilities so it can locate libc in Nix-managed environments, especially NixOS. Ordinary platform apps and roc version alone do not expose that requirement. On macOS, the package installs Roc's bundled minimal Darwin sysroot next to the executable.

Updating sources.json

./update.sh
./update.sh nightly-2026-08-07-8d23662
./update.sh nightly-2026-July-14-c9147c2

The optional argument selects a specific release; otherwise the script uses GitHub's latest-release API. It validates the immutable release, all four expected assets, tag/commit consistency, URLs, and API-provided SHA-256 digests.

Maintainer checks:

nix fmt -- --check
nix flake check --all-systems --no-build
nix flake check
nix run . -- version