It's relevant if I have a requirement that if a file happens to be duplicated, then the once-include mechanism should treat those copies as one object.
This could arise if the code is originally on a system where some header files are symlinks to a common file. These symlinks happen to break (due to the way the code is archived, or on some system that doesn't have symlinks or whatever); they turn into separate copies.
Exclusion that is keyed to a symbol that is encoded in the file has no problem with this; filesystem-id-based excusion doesn't handle the case.
> It's relevant if I have a requirement that if a file happens to be duplicated, then the once-include mechanism should treat those copies as one object.
