Issue with __nextSuper - ember.js

Question

Moving from Ember 1.5.1 to 1.6.0, I've run into an issue with __nextSuper (which has been changing in the last few versions). You can see the offending code here.
And here's the relevant Ember code:
function wrap(func, superFunc) {
function superWrapper() {
var ret, sup = this.__nextSuper; // THIS LINE
this.__nextSuper = superFunc;
ret = apply(this, func, arguments);
this.__nextSuper = sup;
return ret;
}
superWrapper.wrappedFunction = func;
superWrapper.wrappedFunction.__ember_arity__ = func.length;
superWrapper.__ember_observes__ = func.__ember_observes__;
superWrapper.__ember_observesBefore__ = func.__ember_observesBefore__;
superWrapper.__ember_listens__ = func.__ember_listens__;
return superWrapper;
};
What happens is, at some point, the superWrapper function gets called with window as the this value. So when I reach the line marked above, this.__nextSuper comes out to be undefined. But rather than sup simply being undefined, it throws the following error:
TypeError: Cannot read property '__nextSuper' of undefined
The thing is, when I pause in the debugger, this is defined (it's the window object). And when I paste var ret, sup = this.__nextSuper; into the console, it works as expected. And, if I go up the stack frame and check the this value, it's exactly what I expect. So I have no idea why superWrapper suddenly has a bad this value.
Finally, the most interesting part, this only happens in the browser; it works fine in PhantomJS. The changelog didn't seem to list anything to do with __nextSuper as a breaking bugfix, but obviously something has changed. How can I solve this issue?

Answer 1

Ember 1.6 looks to have a requirement on super method being called from the scope of the object hosting the super method (probably a bug, but I'm not positive). In your case you'd want to keep track of the scope, then call the super method using it:
(scope is the object that houses isEqual)
var scope = meta.isEqual ? meta : this.get('store').attributeTypeFor(meta.type);
if (scope.isEqual(server, value)) { ...
instead of (scope is window and explodes in 1.6+)
var isEqual = meta.isEqual || this.get('store').attributeTypeFor(meta.type).isEqual;
if (isEqual(server, value)) { ...
Here's a super simple example showing the problem (1.6+): http://emberjs.jsbin.com/yelesahe/1/edit
And working in 1.5.1: http://emberjs.jsbin.com/zedevudo/1/edit
Issue: https://github.com/emberjs/ember.js/issues/5198