Invalid JS: `[a?.b…]` compiles to invalid JavaScript

[maxnordlund]

I found this today, below is the reduced code to reproduce this error on coffeescript.org.

handler = (error) =>
  if error instanceof Error
    arr.push(error)
  else
    arr.push(error.data?.errors...)
  @showErrors = !!foo.length

var handler;

handler = (function(_this) {
  return function(error) {
    var ref;
    if (error instanceof Error) {
      arr.push(error);
    } else {
      // The loose if-statement is the error
      arr.push.apply(_this,       if ((ref = error.data) != null) {
        ref.errors;
      });
    }
    return _this.showErrors = !!foo.length;
  };
})(this);

[vendethiel]

Whoops, good catch...

[lydell]

Minimal case:

coffee -bpe '[a?.b...]'
var slice = [].slice;

slice.call(  if (typeof a !== "undefined" && a !== null) {
    a.b;
  });

[GeoffreyBooth]

Either a duplicate or else very closely related to #1349.

[GeoffreyBooth]

Fixed by #4644.