revset: make descendants() lazier Previously descendants() would force the provided subset to become a set. In the case of revsets like '(%ld::) - (%ld)' (as used by histedit) this would force the '- (%ld)' set to be evaluated, which produced a set containing every commit in the repo (except %ld). This takes 0.6s on large repos. This changes descendants to trust the subset to implement __contains__ efficiently, which improves the above revset to 0.16s. Shaving 0.4 seconds off of histedit. revset #27: (20000::) - (20000) 0) obsolete feature not enabled but 54243 markers found! ! wall 0.023640 comb 0.020000 user 0.020000 sys 0.000000 (best of 100) 1) obsolete feature not enabled but 54243 markers found! ! wall 0.019589 comb 0.020000 user 0.020000 sys 0.000000 (best of 100) This commit removes the final revset related perf hotspot from histedit. Combined with the previous two patches, they shave a little over 3 seconds off histedit on large repos.