TypeScript Version: 2.1.1

Code

function dec(): Function
{
  return function (target: any, propKey: string, descr: PropertyDescriptor): void
  {
    console.log(target[propKey]);
    //logs undefined
    //propKey has three underscores as prefix, but the method has only two underscores
  };
}

class A
{
  @dec()
  private __foo(bar: string): void
  {
    // do something with bar
  }
}

Expected behavior:
target[propKey] should point to the decorated method

Actual behavior:
target[propKey] is undefined

My workaround is checking the property key in the decorator and deleting the first one underscore at the moment.

As far as I can tell the problem exists since typescript 2.1

Edit: updated code to reproduce problem when compiling