You can just say that this feature is only local to the current file and does not affect included files, nor files that this one is included in. There are alrea

You can just say that this feature is only local to the current file and does not affect included files, nor files that this one is included in. There are already some preprocessor features that act like that, e.g. __FILE__, which contains the name of the current file being parsed and obviously is local to it; or "#pragma once", which indicates the current file should not be parsed if it has already been included once. The information for which file is being parsed currently is not lost after the preprocessor stage, so you can have file-local directives.