Extends a type recursively

types.ts

/**
 * Extends a type recursively.
 *
 * @template T - The base recursive type to be extended.
 * @template Ext - An additional set of properties to be merged into the type.
 * @template Key - The key of the recursive property in T.
 *
 * @example
 * ```ts
 * type Node = {
 *   label: string;
 *   nodes: Node[];
 * };
 *
 * type NodeWithId = ExtendRecursive<Node, { id: string }, "nodes">;
 *
 * // NodeWithId is equivalent to:
 * // {
 * //   label: string;
 * //   id: string;
 * //   nodes: NodeWithId[];
 * // }
 * ```
 */
export type ExtendRecursive<
  T extends Record<string, unknown>,
  Ext extends Record<string, unknown>,
  Key extends keyof T
> = Ext &
  Omit<T, Key> & {
    [K in Key]: ExtendRecursive<T, Ext, Key>[];
  };