os/doc/outputs/overlays.md

Overlays

Writing overlays is a common occurence when using a NixOS system. Therefore, we want to keep the process as simple and straightforward as possible.

Any .nix files declared in this directory will be assumed to be a valid overlay, and will be automatically imported into all hosts, and exported via overlays.<file-basename> as well as packages.<system>.<pkgName> (for valid systems), so all you have to do is write it.

Example

overlays/kakoune.nix:

final: prev: {
  kakoune = prev.kakoune.override {
    configure.plugins = with final.kakounePlugins; [
      (kak-fzf.override { fzf = final.skim; })
      kak-auto-pairs
      kak-buffers
      kak-powerline
      kak-vertical-selection
    ];
  };
}