revlog: move censor logic into main revlog class Previously, the revlog class implemented dummy methods for various censor-related functionality. Revision censoring was (and will continue to be) only possible on filelog instances. So filelog implemented these methods to perform something reasonable. A problem with implementing censoring on filelog is that it assumes filelog is a revlog. Upcoming work to formalize the filelog interface will make this not true. Furthermore, the censoring logic is security-sensitive. I think action-at-a-distance with custom implementation of core revlog APIs in derived classes is a bit dangerous. I think at a minimum the censor logic should live in revlog.py. I was tempted to created a "censored revlog" class that basically pulled these methods out of filelog. But, I wasn't a huge fan of overriding core methods in child classes. A reason to do that would be performance. However, the censoring code only comes into play when: * hash verification fails * delta generation * applying deltas from changegroups The new code is conditional on an instance attribute. So the overhead for running the censored code when the revlog isn't censorable is an attribute lookup. All of these operations are at least a magnitude slower than a Python attribute lookup. So there shouldn't be a performance concern. Differential Revision: https://phab.mercurial-scm.org/D3151