nixos-module/overlay.nix

{ lix, versionSuffix ? "" }:
final: prev:
let
  boehmgc-patched = ((final.boehmgc.override {
    enableLargeConfig = true;
  }).overrideAttrs (o: {
    # cherrypick: boehmgc: disable tests on aarch64-linux
    # https://github.com/NixOS/nixpkgs/pull/309418
    doCheck = !((final.stdenv.isDarwin && final.stdenv.isx86_64) || (final.stdenv.isLinux && final.stdenv.isAarch64));

    patches = (o.patches or [ ]) ++ [
      # for clown reasons this version is newer than the one in lix, we should
      # fix this and update our nixpkgs pin
      (prev.path + "/pkgs/tools/package-management/nix/patches/boehmgc-coroutine-sp-fallback.patch")
    ] ++ final.lib.optionals (final.lib.versionOlder o.version "8.2.6") [
      # https://github.com/ivmai/bdwgc/pull/586
      (builtins.path { path = lix + "/boehmgc-traceable_allocator-public.diff"; name = "boehmgc-traceable_allocator-public.patch"; })
    ];
  })
  );

  lixFunctionArgs = builtins.functionArgs (import (lix + "/package.nix"));
  # fix up build-release-notes being required in older versions of Lix.
  lixPackageBuildReleaseNotes =
      if lixFunctionArgs.build-release-notes or true
      then { }
      else { build-release-notes = null; };

  # This is kind of scary to not override the nix version to pretend to be
  # 2.18 since nixpkgs can introduce new breakage in its Nix unstable CLI
  # usage.
  # https://github.com/nixos/nixpkgs/blob/6afb255d976f85f3359e4929abd6f5149c323a02/nixos/modules/config/nix.nix#L121
  lixPkg = final.callPackage (lix + "/package.nix") ({
    versionSuffix = "-lix${versionSuffix}";
    boehmgc-nix = boehmgc-patched;
  } // lixPackageBuildReleaseNotes);

  # These packages depend on Nix features that Lix does not support
  overridelist_2_18 = [
    "attic-client"
    "nix-du"
    "nix-init"
    "nix-prefetch-git"
    "nixos-option"
    "nurl"
    "prefetch-yarn-deps" # force these onto upstream so we are not regularly rebuilding electron
  ];
  override_2_18 = prev.lib.genAttrs overridelist_2_18 (
    name: prev.${name}.override {
      nix = final.nixVersions.nix_2_18_upstream;
    });

  inherit (prev) lib;

  prefetch-npm-deps-args = lib.functionArgs prev.prefetch-npm-deps.override;
in
override_2_18 //
{
  # used for things that one wouldn't necessarily want to update, but we
  # nevertheless shove it in the overlay and fixed-point it in case one *does*
  # want to do that.
  lix-sources = import ./pins.nix;

  nixVersions = prev.nixVersions // rec {
    # FIXME: do something less scuffed
    nix_2_18 = lixPkg;
    stable = nix_2_18;
    nix_2_18_upstream = prev.nixVersions.nix_2_18;
  };

  nix-eval-jobs = (prev.nix-eval-jobs.override {
    # lix
    nix = final.nixVersions.nix_2_18;
  }).overrideAttrs (old: {
    # FIXME: should this be patches instead?
    src = final.lix-sources.nix-eval-jobs;

    mesonBuildType = "debugoptimized";

    ninjaFlags = old.ninjaFlags or [ ] ++ [ "-v" ];
  });

  # support both having and missing https://github.com/NixOS/nixpkgs/pull/304913
  prefetch-npm-deps =
    if (prefetch-npm-deps-args ? nix) || (prefetch-npm-deps-args == {})
    then prev.prefetch-npm-deps.override {
      nix = final.nixVersions.nix_2_18_upstream;
    }
    else prev.prefetch-npm-deps;

  nix-doc = prev.callPackage ./nix-doc/package.nix { withPlugin = false; };
}