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
$ rm -rf a
$ hg init a
$ cd a
$ echo a > a
$ hg ci -Am0
adding a
$ hg tag t1 # 1
$ hg tag --remove t1 # 2
$ hg co 1
1 files updated, 0 files merged, 0 files removed, 0 files unresolved
$ hg tag -f -r0 t1
$ hg tags
tip 3:a49829c4fc11
t1 0:f7b1eb17ad24
$ cd ..