Trial of typing for https://gist.github.com/hikarinotomadoi/8e61fcfa22deaafcd99c0952e52c5c28

dig.ts

type Digged<T, Keys extends string[]> = DigFunI<T, (...args: Keys) => void>[0];

interface DigFunI<T, F> extends Array<F extends (()=>void) ? T :
  F extends ((key: infer K, ...rest: infer Rest) => void) ?
  K extends keyof T ? (DigFunI<T[K],((...args: Rest)=>void)> extends Array<infer E> ? E : unknown)
  : unknown : unknown>{
}

function dig<T, Keys extends string[]>(obj: T, ...keys: Keys): Digged<T, Keys> {
    let result: any= obj;
    for (const k of keys) {
        result = result[k];
    }
    return result;
}

const y = {
    a: {
      b: {
        c: 10
      }
    }
  }

let f: DigFunI<typeof y, (arg: 'a')=>void>[0];


const a = dig(y, 'a');
console.log(a.b);
const b = dig(y, 'a', 'b');
const c = dig(y, 'a','b','c');
const d = dig(y, 'a','b','xxxxxx');