타입스크립트로 인터페이스 속성에서 꼭 하나는 주어져야하는, 또는 꼭 하나만 주어져야하는 타입 만드는 방법

require.ts

interface ITestObject  {
    a: string
    b: number
    c: Function
    d: string[]
}

type RequireAtLeastOne<T, Keys extends keyof T = keyof T> =
    Pick<T, Exclude<keyof T, Keys>> 
    & {
        [K in Keys]-?: Required<Pick<T, K>> & Partial<Pick<T, Exclude<Keys, K>>>
    }[Keys]

type RequireOnlyOne<T, Keys extends keyof T = keyof T> =
    Pick<T, Exclude<keyof T, Keys>>
    & {
        [K in Keys]-?:
            Required<Pick<T, K>>
            & Partial<Record<Exclude<Keys, K>, undefined>>
    }[Keys]

let needToBeLeastOne: RequireAtLeastOne<ITestObject> = {a: ''}
let needToBeOnlyOne: RequireOnlyOne<ITestObject> = {a: ''}

typescript object conditional optional property type

type RemoveCommonValues<T, TOmit> = {
  [P in keyof T]: TOmit extends Record<P, infer U> ? Exclude<T[P], U> : T[P];
};
type Id<T> = {} & { [P in keyof T]: T[P] }; // flatens out the types to make them more readable can be removed
type ConditionalProps<T, TKey extends keyof TCase, TCase extends Partial<T>> =
  | Id<Omit<T, keyof TCase> & TCase>
  | Id<RemoveCommonValues<T, Pick<TCase, TKey>>>;

type Button = ConditionalProps<
  {
    size: "small" | "large";
    appearance: "solid" | "outline" | "minimal";
    isDisabled?: boolean;
  },
  "appearance" | "size",
  | {
      appearance: "outline";
      size: "small";
      isDisabled: false;
      hasFancyOutline?: boolean;
    }
  | {
      appearance: "minimal";
      size: "small";
      isDisabled: false;
      hasFancyOutline?: boolean;
    }
>;

//  same as
// type Button =
//   | {
//       appearance: "outline";
//       size: "small";
//       isDisabled: false;
//       hasFancyOutline?: boolean | undefined;
//     }
//   | {
//       appearance: "minimal";
//       size: "small";
//       isDisabled: false;
//       hasFancyOutline?: boolean | undefined;
//     }
//   | {
//       size: "large";
//       appearance: "solid";
//       isDisabled?: boolean | undefined;
//     };