Decorator expression evaluation order (not descriptor processing order)

[loganfsmyth]

@sebmck wanted me to verify this over here first, since the spec desugaring examples imply it, but it's non-obvious and Babel currently doesn't seem to follow the implied behavior. I originally noticed this over in #20 but it's separate.

Decorator functions are applied to descriptors bottom-up and are thought of as wrappers. My question is about the order of evaluation of the decorator expression themselves. Are they also meant to be evaluated bottom-up, or top-down? In Python for example, while decorators are applied bottom-up, the expressions are evaluated top-down. To demonstrate:

function fn(arg){
  console.log('evaluated', arg);
  return function(){
    console.log('called', arg)
  };
}


class Example {
  @fn(1)
  @fn(2)
  method(){}
}

would the expected output be

evaluated 1
evaluated 2
called 2
called 1

or

evaluated 2
evaluated 1
called 2
called 1

Babel's current implementation results in #2, which is the opposite of Python's behavior, and also the opposite of the desugared examples, e.g.

fn(1)(fn(2)(...))

which will execute fn(1) first, but will call the result of fn(2) first.

[silkentrance]

+1 for this from me, the order by which the decorators are applied is important and should be bottom up as @loganfsmyth did implement in the interim legacy decorators plugin, which I think should be the basis for any future work.