gen-aspects

gen-aspects is aspect-oriented composition types for Nix module systems: a category-keyed option type that lets a caller declare which keys of an attrset are class content, which are nested sub-aspects, and how includes compose.

The problem it owns: a framework wants to let a value be “networking config” in one branch and “a nested aspect that includes other aspects” in another, classified by a declared key rather than by guessing from shape. gen-aspects is that classification surface — aspectsType, parameterized by the key semantics a framework supplies.

Its type system is re-hosted on gen-merge rather than on nixpkgs: evalModuleTree, the structural types and mkOption/mkMerge stand where lib.types and lib.evalModules used to, with leaf checkers arriving from gen-types through merge. The grammar produces the aspect node set without evalModules at all. It builds on gen-identity, gen-merge, gen-prelude and gen-schema. One roster member builds on gen-aspects: gen-link, for cross-flake federation over the same category classification.

Take it alone

flake.nix

{
  inputs.gen-aspects.url = "github:sini/gen-aspects";
  outputs = { gen-aspects, ... }: {
    lib.aspects = gen-aspects.lib;   # lib + gen-schema are wired in by the flake
  };
}

eval = lib.evalModules {
  modules = [{
    options.aspects = lib.mkOption {
      type = aspects.aspectsType {
        keySemantics = {
          nixos = { category = "class"; };
          homeManager = { category = "class"; };
        };
      };
      default = { };
    };
    config.aspects.networking = {
      nixos.networking.hostName = "myhost";
      nixos.networking.firewall.enable = true;
    };
  }];
};