gen-settings

gen-settings resolves an aspect’s settings — a static, introspectable schema of { default; merge } leaves — against an ordered list of override layers, producing a resolved value plus a full per-field provenance chain.

The problem it owns: “why does this field have this value” needs a real answer once more than one layer can set it — env defaults, host overrides, an explicit per-node value. gen-settings resolves the merge and keeps the chain that produced it, so the answer to “why” is a lookup, not an investigation.

Marked experimental

This hub’s own summary table marks gen-settings experimental, subject to replacement. It works today — the schema/resolution surface below is real and current — but it isn’t the settled framework interface, and building tooling that assumes its shape won’t change is premature.

It has the largest dependency footprint on the roster: gen-algebra, gen-bind, gen-graph, gen-identity, gen-prelude, gen-schema, and gen-types. No roster member currently builds on gen-settings.

Take it alone

let
  genSettings = (import ./lib) {
    prelude = gen-prelude.lib;
    algebra = gen-algebra.lib;
    bind = gen-bind.lib;
    graph = gen-graph.lib;
  };
  inherit (genSettings) mkSchema resolveOne;

  schema = mkSchema {
    aspect = config.aspects.firewall;      # a registry entry (carries id_hash)
    fields = {
      "allowed-tcp" = { default = [ 22 ]; merge = "append"; };
      hostname = { default = "unset"; };   # replace (implicit)
    };
  };

  resolved = resolveOne {
    inherit schema;
    layers = [
      { scope = { env = config.envs.prod; }; rendered = "prod"; via = null;
        value = { "allowed-tcp" = [ 80 ]; }; }
      { scope = { host = den.hosts.axon-01; }; rendered = "axon-01"; via = null;
        value = { "allowed-tcp" = [ 443 ]; hostname = "axon-01"; }; }
    ];
  };
in
resolved.value    # => { "allowed-tcp" = [ 22 80 443 ]; hostname = "axon-01"; }