Valid numerical index tuple

index_tuple.ts

type IndexesKeysOfTuple<T extends any[]> = Exclude<
  keyof T & string,
  keyof any[]
>;

type NumberToString<N extends number | bigint> = `${N}`;

type ValidIndex<T extends any[], I extends number> = any[] extends T
  ? number // T is an array but not a tuple type
  : NumberToString<I> extends IndexesKeysOfTuple<T>
  ? I
  : never;

function fn<T extends any[], I extends number>(
  t: readonly [...T],
  i: ValidIndex<T, I>
): void {
  // ...
}

fn(["hi", "how", "are", "you", "?"] as const, 2);
fn(["hi", "how", "are", "you", "?"], 5); // error

fn(["hi", "how", "are", "you", "?"] as Array<string>, 2);
fn(["hi", "how", "are", "you", "?"] as Array<string>, 5);