A declarative family catalog for a family-rich mutator's configuration.

A plugin that emits many mutation kinds under one mutator module usually exposes a families: option so users can narrow the catalog. This module generates that option's selection-and-validation machinery from one declaration, so every such plugin parses the same grammar — the one Mutare's own {:builtins, except: […]} uses — and fails loudly in the same shapes:

defmodule MyPlugin.Config do
  use Mutare.Mutator.Families,
    plugin: "MyPlugin",
    all: ~w(comparison connective null_predicate string_literal)a,
    opt_in: ~w(string_literal)a
end

use options:

• :all (required) — every family the mutator can emit, ordered; duplicates rejected.
• :opt_in (default []) — the subset excluded from the default set; each must be in :all.
• :plugin (default the using module's name) — the name error messages blame, e.g. "Mutare.Ecto".

The declaration generates, all overridable:

• all_families/0 — the :all list;
• default_families/0 — all -- opt_in, the set used when families: is unset;
• parse_families!/1 — a configured families: value (:default, :all, an explicit list, or {:all | :default, except: […]}) to the enabled MapSet, raising ArgumentError on an unknown family or a malformed except:;
• family_enabled?/2 — whether a family is in a parsed set, or in the set a raw keyword list's families: value parses to;
• @type family — the union of the declared family atoms.

Only selection and validation are generated. What each family means — notes, variant labels, delivery — stays the plugin's, typically alongside this use in its config module. Parse once per run by calling parse_families!/1 from the mutator's Mutare.Mutator.init/1 and reading the result back from context.config; then apply the selection once, in Mutare.Mutator.finalize/2 — Mutare runs it on every produced mutation, on both delivery paths, so producers stay pure and no delivery site can forget the filter.