testing https://stackoverflow.com/a/55480598/2410656

gistfile1.txt

// see https://repl.it/repls/TemporalFrigidScientificcomputing
type DataPropertyNames<T> = {
  [K in keyof T]: T[K] extends Function ? never : K;
}[keyof T];

type DataPropertiesOnly<T> = {
  [P in DataPropertyNames<T>]?: T[P] extends object ? DTO<T[P]> : T[P]
};

export type DTO<T> = DataPropertiesOnly<T>;

interface X {
    duration_msec: number;
    available(now: number): boolean;
}

let x:DTO<X> = {
  // this should be an error
  // because it is missing
  // duration_msec.
};
let y:X = {
  ...x
}
console.log("x", x);
console.log("y", y);