Unused JS conditional var in unused function crashes QQmlEngine

Reproduced on a variety of platforms:

import QtQuick 2.7
import QtQuick.Window 2.2

Window {
  id: main
  visible: true
  width: 500
  height: 300

  function foo() {
    var c = main.width > 1 ? 27 : -147
  }
}

The conditional has to be used and the var has to be unused, otherwise it doesn't crash. The function doesn't need to be executed, it crashes during QQmlEngine.load()