Extra _ref variable created for no reason

[devongovett]

If I compile this with the latest version of CoffeeScript:

Array.isArray ?= (object) ->
    Object.prototype.toString.call(object) is '[object Array]'

I get this:

var _ref;

if ((_ref = Array.isArray) == null) {
  Array.isArray = function(object) {
    return Object.prototype.toString.call(object) === '[object Array]';
  };
}

Which has an extra _ref variable that is never used. Probably should just simplify that to:

if (Array.isArray == null) {
  Array.isArray = function(object) {
    return Object.prototype.toString.call(object) === '[object Array]';
  };
}

[michaelficarra]

Confirmed. Minimal test case: a.b ?= c

var _ref;

if ((_ref = a.b) == null) a.b = c;

edit: To whoever works on this: be careful because _ref is used when the result of the existential assignment is used:

$ coffee -bep 'a = (b.c ?= d)'
var a, _ref;

a = ((_ref = b.c) != null ? _ref : b.c = d);

[jashkenas]

The above commit should fix this case -- where the existential assignment occurs at the top level, we know that there's no need to cache the ref.

[haberbyte]

This reoccurs in current master, is there a reason the commit got revoked?

[haberbyte]

@jashkenas : This issue appears to be related!

#2197

There is a fix in there that causes this "useless" _ref variable to reappear.
Is there a way to fix both issues?