// custom mainClass only works with hotwire_here
static Class<?> hotwire(S src, IF1<ClassLoader, S> calculateMainClass default lambda1 mainClassNameForClassLoader) {
  assertFalse(_inCore());
  Class j = getJavaX();
  if (isAndroid()) {
    synchronized(j) { // hopefully this goes well...
      List<File> libraries = new ArrayList<File>();
      File srcDir = (File) call(j, "transpileMain", src, libraries);
      if (srcDir == null)
        fail("transpileMain returned null (src=" + quote(src) + ")");
    
      Object androidContext = get(j, "androidContext");
      return (Class) call(j, "loadx2android", srcDir, src);
    }
  } else {
    ifdef hotwire_here
    ret hotwire_overInternalBot(src, calculateMainClass);
    endifdef
    ifndef hotwire_here
    Class c = cast call(j, "hotwire", src);
    hotwire_copyOver(c);
    ret c;
    endifndef
  }
}

Began life as a copy of #1000963