filecache: unimplement __set__() and __delete__() (API) Implementing __set__() implies that the descriptor can't be overridden by obj.__dict__, which means any property access involves slow function call. "Data descriptors with __set__() and __get__() defined always override a redefinition in an instance dictionary. In contrast, non-data descriptors can be overridden by instances." https://docs.python.org/2.7/reference/datamodel.html#invoking-descriptors This patch basically backs out 236bb604dc39, "scmutil: update cached copy when filecached attribute is assigned (issue3263)." The problem described in issue3263 (which is #3264 in Bugzilla) should no longer happen since repo._bookmarkcurrent has been moved to repo._bookmarks.active. We still have a risk of introducing similar bugs, but I think that's the cost we have to pay. $ hg perfrevset 'branch(tip)' -R mercurial (orig) wall 0.139511 comb 0.140000 user 0.140000 sys 0.000000 (best of 66) (prev) wall 0.114195 comb 0.110000 user 0.110000 sys 0.000000 (best of 81) (this) wall 0.099038 comb 0.110000 user 0.100000 sys 0.010000 (best of 93)