Func A($query)
  $a = "test";
  $query->whereHas('rel', Func ($query) use ($a)
    $query->where('col', $a)
  EndFunc)
EndFunc

becomes

Func A($query)
  $query->whereHas('rel', B)
EndFunc

Func B($query, $au3p_use);B would be a autogenerated name
  ;unpack vars here from $au3p_use with for and assign, we exspect map or array [*][2] [0]=key [1]=value

  $query->where('col', $a)
EndFunc