describe-object.ts

type IfEquals<X, Y, A, B> = (<T>() => T extends X ? 1 : 2) extends (<T>() => T extends Y ? 1 : 2) ? A : B;
type ReadonlyKeys<U, T = { [K in keyof U]-?: U[K] }> = {
  [P in keyof T]: IfEquals<{ [Q in P]: T[P] }, { -readonly [Q in P]: T[P] }, never, P>
}[keyof T];
type Full<T, R = ReadonlyKeys<T>> = {
  -readonly [K in keyof T]-?: {
    type: T[K],
    optional: T extends Record<K, any> ? false : true,
    readonly: K extends R ? true : false,
  }
}
type Unfuck<T> = T extends infer R ? {[K in keyof R]: R[K]} : never;
type Test<T> = {a?: any} extends { [K in keyof T as 'a']: T[K] } ? 'bar' : 'foo'
type First<U> = {
  [K in keyof U as Test<Partial<U> & Record<K, U[K]>>]: K
} extends {foo: infer R} ? R : 1
type DescribeIter<T, R = First<T>> = R extends string
  ? T extends Record<R, any>
    ? [
      Unfuck<{name: R} & T[R]>,
      ...DescribeIter<Unfuck<Omit<T, R>>>
    ]
    : never
  : []
type Describe<T> = DescribeIter<Full<T>>

type R = Describe<{
  a?: number, 
  b: string, 
  readonly c: boolean, 
  readonly d?: 'e',
}>