gen-schema

gen-schema is a typed record registry for Nix with extension points, strict validation, refinement contracts, identity hashing, cross-instance references, first-class mixins, introspection, and declarative methods — built on the pure-gen module system, with no nixpkgs.lib dependency.

The problem it owns: a fleet of typed instances — hosts, users, anything with a declared shape and a registry of concrete values — needs one place that validates them, hashes them for identity, and lets one instance reference another by that identity. gen-schema is that place.

It depends on gen-algebra, gen-identity, gen-merge, and gen-prelude. That gen-merge dependency is the roster’s one ruled exception to the strata ordering: gen-schema sits in substrate by role, but it declares kinds whose fields are options, so it’s written in the module system’s language and reaches sideways into gen-merge. Four roster members build on gen-schema in turn: gen-aspects, gen-link, gen-scope, and gen-settings.

Take it alone

flake.nix

{
  inputs.gen-schema.url = "github:sini/gen-schema";
  inputs.flake-parts.url = "github:hercules-ci/flake-parts";

  outputs = inputs: inputs.flake-parts.lib.mkFlake { inherit inputs; } {
    imports = [ inputs.gen-schema.flakeModules.default ];

    schema.host = {
      options.addr = lib.mkOption { type = lib.types.str; };
      options.role = lib.mkOption { type = lib.types.str; default = "worker"; };
    };

    options.hosts = genSchema.mkInstanceRegistry config.schema.host { };
    hosts.igloo = { addr = "10.0.1.1"; role = "web"; };
    hosts.iceberg = { addr = "10.0.2.1"; };  # role defaults to "worker"

    flake.fleet = {
      iglooAddr = config.hosts.igloo.addr;     # → "10.0.1.1"
      iglooHash = config.hosts.igloo.id_hash;  # → "host:<deterministic SHA-256>"
    };
  };
}

The flake-parts module ships default settings (strict = true, no baseModule). For a custom strict, baseModule, collections, or computed, use the programmatic API directly.