cpp: how to use macro argument as dataflow sink

[k4lizen]

I would like to do something like this:

  predicate isSink(DataFlow::Node sink) {
    exists(MacroInvocation m |
      sink.asExpr() = m.getArgument(0)
      and m.getTarget().getName() = "my_cool_macro"
    )
  }

But getArgument is not defined, and getExpandedArgument returns a string. Doing sink.asExpr().toString() = m.getExpandedArgument(0) returns zero matches.

How do I use macros in dataflow?