export type ConditionalKeys<Base, Condition> = NonNullable<
  // Wrap in `NonNullable` to strip away the `undefined` type from the produced union.
  {
    // Map through all the keys of the given base type.
    [Key in keyof Base]: Base[Key] extends Condition // Pick only keys with types extending the given `Condition` type.
      ? // Retain this key since the condition passes.
        Key
      : // Discard this key since the condition fails.
        never

    // Convert the produced object into a union type of the keys which passed the conditional test.
  }[keyof Base]
>

export type ConditionalPick<Base, Condition> = Pick<
  Base,
  ConditionalKeys<Base, Condition>
>