subsetmaker: stabilize the computation of `scratch` subset

`heads` is set, order of the element are not deterministic and we need to
stabilize that if we want to get reproducible results.

Differential Revision: https://phab.mercurial-scm.org/D12394

contrib/perf-utils/subsetmaker.py

@@ -1,170 +1,172 b''
 """revset to select sample of repository
 
 Hopefully this is useful to create interesting discovery cases.
 """
 
 import collections
 import random
 
 from mercurial.i18n import _
 
 from mercurial import (
     registrar,
     revset,
     revsetlang,
     smartset,
 )
 
 revsetpredicate = registrar.revsetpredicate()
 
 
 @revsetpredicate(b'subsetspec("<spec>")')
 def subsetmarkerspec(repo, subset, x):
     """use a shorthand spec as used by search-discovery-case
 
     Supported format are:
 
     - "scratch-count-seed": not scratch(all(), count, "seed")
     - "randomantichain-seed": ::randomantichain(all(), "seed")
     - "rev-REV": "::REV"
     """
     args = revsetlang.getargs(
         x, 0, 1, _(b'subsetspec("spec") required an argument')
     )
 
     spec = revsetlang.getstring(args[0], _(b"spec should be a string"))
     case = spec.split(b'-')
     t = case[0]
     if t == b'scratch':
         spec_revset = b'not scratch(all(), %s, "%s")' % (case[1], case[2])
     elif t == b'randomantichain':
         spec_revset = b'::randomantichain(all(), "%s")' % case[1]
     elif t == b'rev':
         spec_revset = b'::%d' % case[1]
     else:
         assert False, spec
 
     selected = repo.revs(spec_revset)
 
     return selected & subset
 
 
 @revsetpredicate(b'scratch(REVS, <count>, [seed])')
 def scratch(repo, subset, x):
     """randomly remove <count> revision from the repository top
 
     This subset is created by recursively picking changeset starting from the
     heads. It can be summarized using the following algorithm::
 
         selected = set()
         for i in range(<count>):
             unselected = repo.revs("not <selected>")
             candidates = repo.revs("heads(<unselected>)")
             pick = random.choice(candidates)
             selected.add(pick)
     """
     m = _(b"scratch expects revisions, count argument and an optional seed")
     args = revsetlang.getargs(x, 2, 3, m)
     if len(args) == 2:
         x, n = args
         rand = random
     elif len(args) == 3:
         x, n, seed = args
         seed = revsetlang.getinteger(seed, _(b"seed should be a number"))
         rand = random.Random(seed)
     else:
         assert False
 
     n = revsetlang.getinteger(n, _(b"scratch expects a number"))
 
     selected = set()
     heads = set()
     children_count = collections.defaultdict(lambda: 0)
     parents = repo.changelog._uncheckedparentrevs
 
     baseset = revset.getset(repo, smartset.fullreposet(repo), x)
     baseset.sort()
     for r in baseset:
         heads.add(r)
 
         p1, p2 = parents(r)
         if p1 >= 0:
             heads.discard(p1)
             children_count[p1] += 1
         if p2 >= 0:
             heads.discard(p2)
             children_count[p2] += 1
 
     for h in heads:
         assert children_count[h] == 0
 
     selected = set()
     for x in range(n):
         if not heads:
             break
-        pick = rand.choice(list(heads))
+        pickable = list(heads)
+        pickable.sort()
+        pick = rand.choice(pickable)
         heads.remove(pick)
         assert pick not in selected
         selected.add(pick)
         p1, p2 = parents(pick)
         if p1 in children_count:
             assert p1 in children_count
             children_count[p1] -= 1
             assert children_count[p1] >= 0
             if children_count[p1] == 0:
                 assert p1 not in selected, (r, p1)
                 heads.add(p1)
         if p2 in children_count:
             assert p2 in children_count
             children_count[p2] -= 1
             assert children_count[p2] >= 0
             if children_count[p2] == 0:
                 assert p2 not in selected, (r, p2)
                 heads.add(p2)
 
     return smartset.baseset(selected) & subset
 
 
 @revsetpredicate(b'randomantichain(REVS, [seed])')
 def antichain(repo, subset, x):
     """Pick a random anti-chain in the repository
 
     A antichain is a set of changeset where there isn't any element that is
     either a descendant or ancestors of any other element in the set. In other
     word, all the elements are independant. It can be summarized with the
     following algorithm::
 
     selected = set()
     unselected = repo.revs('all()')
     while unselected:
         pick = random.choice(unselected)
         selected.add(pick)
         unselected -= repo.revs('::<pick> + <pick>::')
     """
 
     args = revsetlang.getargs(
         x, 1, 2, _(b"randomantichain expects revisions and an optional seed")
     )
     if len(args) == 1:
         (x,) = args
         rand = random
     elif len(args) == 2:
         x, seed = args
         seed = revsetlang.getinteger(seed, _(b"seed should be a number"))
         rand = random.Random(seed)
     else:
         assert False
 
     selected = set()
 
     baseset = revset.getset(repo, smartset.fullreposet(repo), x)
     undecided = baseset
 
     while undecided:
         pick = rand.choice(list(undecided))
         selected.add(pick)
         undecided = repo.revs(
             '%ld and not (::%ld or %ld::head())', baseset, selected, selected
         )
 
     return smartset.baseset(selected) & subset