From #2055 :

We currently report about suppressed violations, but we don't report about "unused suppression markers"

More generally, it would be nice to have a rule to detect unused @SuppressWarnings. Eg a @SuppressWarnings("unchecked") when a compiler wouldn't report any unchecked warning anyway.

I was thinking, whether this could be part of this ViolationSuppressor interface? Something like getAllSuppressionMarkers() for a file. So that this functionality needs to be provided as part of the language implementation. We would then somehow figure out afterwards, which of the markers have been used...