Lix NixOS module

See the official installation guide for details on usage of release versions.

See the beta guide for a setup guide on how to use HEAD:

What does this do?

This is an overlay wrapped in a NixOS module that will replace CppNix with Lix in nixpkgs. This is useful so that nixos-rebuild, nix-direnv and similar will use Lix.

Optionally, it can build Lix from source.

Versioning with Lix

The version of this overlay should match the major Lix version, and if running HEAD, it should be the latest available version of the overlay. Breaking changes to the overlay are shamelessly done on HEAD.

The version of Lix pinned in this flake's flake.lock is a version of Lix that is expected to work, however if running HEAD, it can be assumed to work with HEAD as well if both lix-nixos-module and lix are the latest version.

Common pitfalls

Various flake frameworks such as flake-parts and snowfall (and possibly Colmena in the future if they do a similar optimization) manage overlays separately from NixOS, since they provide pkgs pre-imported to NixOS. This saves a couple of seconds of evaluation time and resources, but it means that the NixOS option nixpkgs.overlays is completely ignored on these frameworks.

If you are using such a framework, add overlays.default to the overlays list for said framework.

Flake structure and usage

The flake here has two inputs of note:

nixpkgs, which is unused for most people. It is purely used for checks in developing lix-nixos-module itself.

The installation instructions make it follows to make flake.lock less confusing, but it is nonetheless unused.
lix, which determines the version of Lix to do source builds for, if doing source builds.

These are the most relevant outputs for most people:

nixosModules.lixFromNixpkgs - uses Lix from nixpkgs and installs the overlay to use Lix on a NixOS system. This is only useful for a stable version of Lix, and cannot be used for running HEAD.
nixosModules.default - uses Lix from source and installs the overlay to use Lix on a NixOS system.
overlays.lixFromNixpkgs - overlay to use Lix from nixpkgs in place of Nix.
overlays.default - overlay to use Lix from source in place of Nix.

Non-flake usage

Import module.nix or overlay.nix as desired, with the arguments lix (derivation-like attribute set with the Lix sources, or null to use Lix from nixpkgs) and versionSuffix (optional string).

It's desirable to also include a versionSuffix like the following while building HEAD from source, to have nix --version include date and commit information. To get such metadata, it depends on which pinning system is in use, but builtins.fetchGit will provide the necessary metadata for the following to work:

versionSuffix = "pre${builtins.substring 0 8 lix.lastModifiedDate}-${lix.shortRev or lix.dirtyShortRev}";

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