wrong warning: side-effects from mutating the binding

[NTillmann]

Prepacking this program...

(function() {
  function fn(arg) {
    if (arg) return undefined;
    let f = 42;
    return f;
  }
  __optimize(fn);
})();

gives the following warning:

side-effects from mutating the binding "f" at location: 4:12 - 4:4

Why?

[trueadm]

Looks like an ES6 feature bug. Do we have a tag for ES6 features?

[NTillmann]

Yes, we do :-) Not sure if it's just ES6 related. The warning goes away when I remove the if statement.