opam-nix

Turn opam-based OCaml projects into Nix derivations, automatically resolving both OCaml and system dependencies.

opam-nix can build packages

• from opam and dune-project files,
• for Linux and macOS,
• on x86_64 and aarch64 (including M1 macs),
• using a compiler from nixpkgs or from opam-repository,
• with either dynamic or static linking.

It also comes with the power of Nix, allowing you to effortlessly manage multiple projects with different dependency versions, override dependencies, cache builds, and more.

Quick start

For a quick introduction to opam-nix and a guide to get you started, read this blog post on the Tweag blog.

Templates

opam-nix comes with some templates that can help you package opam packages with Nix.

Note

All of these templates assume that you already have an OCaml project packaged with opam, and just want to package it with Nix. If you're starting from scratch, you have to set up the opam files separately. The easiest way to do this is by running nix-shell -p dune_3 --run "dune init project <project_name> ."

• A simple package build, no frills: nix flake init -t github:tweag/opam-nix
• A more featured flake, building an executable and providing a shell in which you can conveniently work on it: nix flake init -t github:tweag/opam-nix#executable
• Build multiple packages from the same workspace, and have a shell in which you can work on them: nix flake init -t github:tweag/opam-nix#multi-package

Note

If you're using Git, you should git add flake.nix after initializing, as Nix operates on the git index contents.

Examples

There are also some examples which can give you some ideas of what is possible with opam-nix:

• Building a package from opam-repository
• Building a package from a custom github repository
• Building a package from a multi-package github repository with submodules
• Building a Rocq package
• Building a static version of a package using compiler from nixpkgs
• Building a static version of a package using the compiler from opam
• Building a GUI package
• Building the entirety of Tezos

All examples are checks and packages, so you can do e.g. nix build github:tweag/opam-nix#opam-ed to try them out individually, or nix flake check github:tweag/opam-nix to build them all.

Building packages from opam-repository with Nix

opam-nix provides all packages from opam-repository in its legacyPackages flake output. You can use this to quickly check out some package, or get a shell with particular version without messing with opam switches.

For example:

• nix build 'github:tweag/opam-nix#utop."2.10.0"' to build a specific version of utop (available in ./result),
• nix shell github:tweag/opam-nix#camyll.latest to get a shell with the latest version of camyll.

Complete documentation

Complete documentation for opam-nix is available in the DOCUMENTATION.md file.

Questions? Problems?

You can reach out to us via the Discussions page or directly to the maintainer via email.

Related projects

• Nix: A powerful package manager that makes package management reliable and reproducible;
• opam: the OCaml package manager;
• hillingar: Tool for building MirageOS unikernels with opam-nix.