Not inferring return type for Object.prototype extension

[dyst5422]

TypeScript Version: 2.3.2

Code

code.ts

Object.prototype.myGet = function myGet() {
  return this
};

const a = { prop1: 2 };

console.log(a.myGet().prop1);

types.d.ts

interface Object {
  myGet(): this;
}

Expected behavior:
Should be able to have correct type on the return of a.get() such that it should know that prop1 exists
Actual behavior:
on compile
TSError: Property 'prop1' does not exist on type 'Object'

[dyst5422]

just found #12507 closing