Smoosh Typed

type UnionToIntersection<U> = (
  U extends any ? (k: U) => void : never
) extends (k: infer I) => void
  ? I
  : never

type SubpropertyMerge<T> = (
  T extends object ? (
    T extends string | number | ((...args: any) => any) | symbol | boolean ? T
    : { [K in keyof T]: SubpropertyMerge<T[K]> }
  ) : T
);


function smoosh<T extends object>(objs: T[]): SubpropertyMerge<UnionToIntersection<T>> {
  let out = {} as any;
  Object.entries(objs).forEach(([key, value]) => {
    if (typeof value === "object" && out[key]) {
      out[key] = smoosh([out[key], value]);
    } else {
      out[key] = value;
    }
  })
  return out;
}

// if you don't define the generic, this won't work
const eg = smoosh<
  { foo: {a: 1}}
  | { foo: {b: 2}}
>([
  { foo: {a: 1}},
  { foo: {b: 2}}
]);

eg.foo.a
eg.foo.b