The language I'm using doesn't let me express the public/private divide I wish to make correctly (e.g. "private" implementation functions for a public C macro.)

The language I'm using doesn't let me express the public/private divide I wish to make correctly (e.g. "private" implementation functions for a public C macro.) The API is 100% intended for internal use only, but someone insists on ignoring that and consuming the private API anyways. Instead of forcing them to write their own headers which silently break at runtime when function signatures change in certain calling conventions which don't check those signatures, I instead allow them to include headers with a few keywords like "private", "internal", "do_not_use", or "i_am_voiding_my_semver_warranty" in the path, perhaps only after they make some similarly scary #define s, so it's at least a build failure.