Argument names cannot be renamed in sub macro

Created by: tuchida

example:

macro main {
  case ($a) => {
    (function(foo) {
      var bar = 1 + foo;
      return sub($a);
    })(2);
  }
}

macro sub {
  case ($a) => {
    foo + bar + $a
  }
}

main(3);

output:

(function (foo$1) {
    var bar = 1 + foo$1;
    return foo + bar + 3;
}(2));
;

I expect return foo$1 + bar + 3; or do not rename of the foo.

(I read expander.js, but I did not find how to fix this issue. Probably, variable identifiers is not to renamed. Because getVarIdentifiers is returning an empty array.)