revset: add startdepth limit to ancestors() as internal option This is necessary to implement the set{gen} (set subscript) operator. For example, set{-n} will be translated to ancestors(set, depth=n, startdepth=n). https://www.mercurial-scm.org/wiki/RevsetOperatorPlan#ideas_from_mpm The UI is undecided and I doubt if the startdepth option would be actually useful, so the option is hidden for now. 'depth' could be extended to take min:max range, in which case, integer depth should select a single generation. ancestors(set, depth=:y) # scan up to y-th generation ancestors(set, depth=x:) # skip until (x-1)-th generation ancestors(set, depth=x) # select only x-th generation Any ideas are welcomed. # reverse(ancestors(tip)) using hg repo 3) 0.075951 4) 0.076175