`port provides` equivalent in Portfile?

[René J.V. Bertin]

Hi,

There's a PortGroup that allows a Portfile to verify which variant of a given other port is active. Is it possible too to do the equivalent operation of `port provides` from inside a Portfile .
Context: 2 port families (KDE4 and KF5) that have partial overlaps. Not much one can do about it if a hard conflict isn't justified, so I provide *compat variants where possible, to use components installed by the one port in the other.
That works well enough, but I'd like to be able to print a warning that that variant isn't required by checking if at least one of those overlap files exist and do not belong to (a previous version of) the current port.

NB: `port provides` itself doesn't work for me for some reason, but when conflicts arise when I active a port it turns out that the underlying information is available after all (file "f" belongs to port "p").

Thanks,
R.