revset: add depth limit to descendants() (
issue5374)
This is naive implementation using two-pass scanning. Tracking descendants
isn't an easy problem if both start and stop depths are specified. It's
impractical to remember all possible depths of each node while scanning from
roots to descendants because the number of depths explodes. Instead, we could
cache (min, max) depths as a good approximation and track ancestors back when
needed, but that's likely to have off-by-one bug.
Since this implementation appears not significantly slower, and is quite
straightforward, I think it's good enough for practical use cases. The time
and space complexity is O(n) ish.
revisions:
0) 1-pass scanning with (min, max)-depth cache (worst-case quadratic)
1) 2-pass scanning (this version)
repository:
mozilla-central
# descendants(0) (for reference)
*) 0.430353
# descendants(0, depth=1000)
0) 0.264889
1) 0.398289
# descendants(limit(tip:0, 1, offset=10000), depth=1000)
0) 0.025478
1) 0.029099
# descendants(0, depth=2000, startdepth=1000)
0) painfully slow (due to quadratic backtracking of ancestors)
1) 1.531138
dagop: make walk direction switchable so it can track descendants
# ancestors(tip) using hg repo
2) 0.068527
3) 0.069097
dagop: factor out generator of ancestor nodes
# ancestors(tip) using hg repo
1) 0.068976
2) 0.068527
dagop: factor out pfunc from revancestors() generator
This generator will be reused for tracking descendants with depth limit.
# ancestors(tip) using hg repo
0) 0.065868
1) 0.068976
dagop: use smartset.min() in revdescendants() generator
All callers pass the result of revset.getset(), which should be a smartset.
dagop: change revdescendants() to include all root revisions
Prepares for adding depth support. I want to process depth=0 in
revdescendants() to make things simpler.
only() also calls dagop.revdescendants(), but it filters out root revisions
explicitly. So this should cause no problem.
# descendants(0) using hg repo
0) 0.052380
1) 0.051226
# only(tip) using hg repo
0) 0.001433
1) 0.001425
test-revset: add a few more tests of descendants()
I'll add depth support to descendants().