hbisect: use a defaultdict to avoid large allocations for a large changelogs

We can avoid a SPACE(len(changelog)) allocation by using a defaultdict.

Test Plan:
    python run-tests.py test-bisect*

Differential Revision: https://phab.mercurial-scm.org/D1499

mercurial/hbisect.py

@@ -1,300 +1,300
 # changelog bisection for mercurial
 #
 # Copyright 2007 Matt Mackall
 # Copyright 2005, 2006 Benoit Boissinot <[e-mail]>
 #
 # Inspired by git bisect, extension skeleton taken from mq.py.
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 from __future__ import absolute_import
 
 import collections
 
 from .i18n import _
 from .node import (
     hex,
     short,
 )
 from . import (
     error,
 )
 
 def bisect(repo, state):
     """find the next node (if any) for testing during a bisect search.
     returns a (nodes, number, good) tuple.
 
     'nodes' is the final result of the bisect if 'number' is 0.
     Otherwise 'number' indicates the remaining possible candidates for
     the search and 'nodes' contains the next bisect target.
     'good' is True if bisect is searching for a first good changeset, False
     if searching for a first bad one.
     """
 
     changelog = repo.changelog
     clparents = changelog.parentrevs
     skip = set([changelog.rev(n) for n in state['skip']])
 
     def buildancestors(bad, good):
         badrev = min([changelog.rev(n) for n in bad])
-        ancestors = [None] * (len(changelog) + 1)
+        ancestors = collections.defaultdict(lambda: None)
         for rev in repo.revs("descendants(%ln) - ancestors(%ln)", good, good):
             ancestors[rev] = []
         if ancestors[badrev] is None:
             return badrev, None
         return badrev, ancestors
 
     good = False
     badrev, ancestors = buildancestors(state['bad'], state['good'])
     if not ancestors: # looking for bad to good transition?
         good = True
         badrev, ancestors = buildancestors(state['good'], state['bad'])
     bad = changelog.node(badrev)
     if not ancestors: # now we're confused
         if (len(state['bad']) == 1 and len(state['good']) == 1 and
             state['bad'] != state['good']):
             raise error.Abort(_("starting revisions are not directly related"))
         raise error.Abort(_("inconsistent state, %s:%s is good and bad")
                          % (badrev, short(bad)))
 
     # build children dict
     children = {}
     visit = collections.deque([badrev])
     candidates = []
     while visit:
         rev = visit.popleft()
         if ancestors[rev] == []:
             candidates.append(rev)
             for prev in clparents(rev):
                 if prev != -1:
                     if prev in children:
                         children[prev].append(rev)
                     else:
                         children[prev] = [rev]
                         visit.append(prev)
 
     candidates.sort()
     # have we narrowed it down to one entry?
     # or have all other possible candidates besides 'bad' have been skipped?
     tot = len(candidates)
     unskipped = [c for c in candidates if (c not in skip) and (c != badrev)]
     if tot == 1 or not unskipped:
         return ([changelog.node(c) for c in candidates], 0, good)
     perfect = tot // 2
 
     # find the best node to test
     best_rev = None
     best_len = -1
     poison = set()
     for rev in candidates:
         if rev in poison:
             # poison children
             poison.update(children.get(rev, []))
             continue
 
         a = ancestors[rev] or [rev]
         ancestors[rev] = None
 
         x = len(a) # number of ancestors
         y = tot - x # number of non-ancestors
         value = min(x, y) # how good is this test?
         if value > best_len and rev not in skip:
             best_len = value
             best_rev = rev
             if value == perfect: # found a perfect candidate? quit early
                 break
 
         if y < perfect and rev not in skip: # all downhill from here?
             # poison children
             poison.update(children.get(rev, []))
             continue
 
         for c in children.get(rev, []):
             if ancestors[c]:
                 ancestors[c] = list(set(ancestors[c] + a))
             else:
                 ancestors[c] = a + [c]
 
     assert best_rev is not None
     best_node = changelog.node(best_rev)
 
     return ([best_node], tot, good)
 
 def extendrange(repo, state, nodes, good):
     # bisect is incomplete when it ends on a merge node and
     # one of the parent was not checked.
     parents = repo[nodes[0]].parents()
     if len(parents) > 1:
         if good:
             side = state['bad']
         else:
             side = state['good']
         num = len(set(i.node() for i in parents) & set(side))
         if num == 1:
             return parents[0].ancestor(parents[1])
     return None
 
 def load_state(repo):
     state = {'current': [], 'good': [], 'bad': [], 'skip': []}
     for l in repo.vfs.tryreadlines("bisect.state"):
         kind, node = l[:-1].split()
         node = repo.lookup(node)
         if kind not in state:
             raise error.Abort(_("unknown bisect kind %s") % kind)
         state[kind].append(node)
     return state
 
 
 def save_state(repo, state):
     f = repo.vfs("bisect.state", "w", atomictemp=True)
     with repo.wlock():
         for kind in sorted(state):
             for node in state[kind]:
                 f.write("%s %s\n" % (kind, hex(node)))
         f.close()
 
 def resetstate(repo):
     """remove any bisect state from the repository"""
     if repo.vfs.exists("bisect.state"):
         repo.vfs.unlink("bisect.state")
 
 def checkstate(state):
     """check we have both 'good' and 'bad' to define a range
 
     Raise Abort exception otherwise."""
     if state['good'] and state['bad']:
         return True
     if not state['good']:
         raise error.Abort(_('cannot bisect (no known good revisions)'))
     else:
         raise error.Abort(_('cannot bisect (no known bad revisions)'))
 
 def get(repo, status):
     """
     Return a list of revision(s) that match the given status:
 
     - ``good``, ``bad``, ``skip``: csets explicitly marked as good/bad/skip
     - ``goods``, ``bads``      : csets topologically good/bad
     - ``range``              : csets taking part in the bisection
     - ``pruned``             : csets that are goods, bads or skipped
     - ``untested``           : csets whose fate is yet unknown
     - ``ignored``            : csets ignored due to DAG topology
     - ``current``            : the cset currently being bisected
     """
     state = load_state(repo)
     if status in ('good', 'bad', 'skip', 'current'):
         return map(repo.changelog.rev, state[status])
     else:
         # In the following sets, we do *not* call 'bisect()' with more
         # than one level of recursion, because that can be very, very
         # time consuming. Instead, we always develop the expression as
         # much as possible.
 
         # 'range' is all csets that make the bisection:
         #   - have a good ancestor and a bad descendant, or conversely
         # that's because the bisection can go either way
         range = '( bisect(bad)::bisect(good) | bisect(good)::bisect(bad) )'
 
         _t = repo.revs('bisect(good)::bisect(bad)')
         # The sets of topologically good or bad csets
         if len(_t) == 0:
             # Goods are topologically after bads
             goods = 'bisect(good)::'    # Pruned good csets
             bads  = '::bisect(bad)'     # Pruned bad csets
         else:
             # Goods are topologically before bads
             goods = '::bisect(good)'    # Pruned good csets
             bads  = 'bisect(bad)::'     # Pruned bad csets
 
         # 'pruned' is all csets whose fate is already known: good, bad, skip
         skips = 'bisect(skip)'                 # Pruned skipped csets
         pruned = '( (%s) | (%s) | (%s) )' % (goods, bads, skips)
 
         # 'untested' is all cset that are- in 'range', but not in 'pruned'
         untested = '( (%s) - (%s) )' % (range, pruned)
 
         # 'ignored' is all csets that were not used during the bisection
         # due to DAG topology, but may however have had an impact.
         # E.g., a branch merged between bads and goods, but whose branch-
         # point is out-side of the range.
         iba = '::bisect(bad) - ::bisect(good)'  # Ignored bads' ancestors
         iga = '::bisect(good) - ::bisect(bad)'  # Ignored goods' ancestors
         ignored = '( ( (%s) | (%s) ) - (%s) )' % (iba, iga, range)
 
         if status == 'range':
             return repo.revs(range)
         elif status == 'pruned':
             return repo.revs(pruned)
         elif status == 'untested':
             return repo.revs(untested)
         elif status == 'ignored':
             return repo.revs(ignored)
         elif status == "goods":
             return repo.revs(goods)
         elif status == "bads":
             return repo.revs(bads)
         else:
             raise error.ParseError(_('invalid bisect state'))
 
 def label(repo, node):
     rev = repo.changelog.rev(node)
 
     # Try explicit sets
     if rev in get(repo, 'good'):
         # i18n: bisect changeset status
         return _('good')
     if rev in get(repo, 'bad'):
         # i18n: bisect changeset status
         return _('bad')
     if rev in get(repo, 'skip'):
         # i18n: bisect changeset status
         return _('skipped')
     if rev in get(repo, 'untested') or rev in get(repo, 'current'):
         # i18n: bisect changeset status
         return _('untested')
     if rev in get(repo, 'ignored'):
         # i18n: bisect changeset status
         return _('ignored')
 
     # Try implicit sets
     if rev in get(repo, 'goods'):
         # i18n: bisect changeset status
         return _('good (implicit)')
     if rev in get(repo, 'bads'):
         # i18n: bisect changeset status
         return _('bad (implicit)')
 
     return None
 
 def shortlabel(label):
     if label:
         return label[0].upper()
 
     return None
 
 def printresult(ui, repo, state, displayer, nodes, good):
     if len(nodes) == 1:
         # narrowed it down to a single revision
         if good:
             ui.write(_("The first good revision is:\n"))
         else:
             ui.write(_("The first bad revision is:\n"))
         displayer.show(repo[nodes[0]])
         extendnode = extendrange(repo, state, nodes, good)
         if extendnode is not None:
             ui.write(_('Not all ancestors of this changeset have been'
                        ' checked.\nUse bisect --extend to continue the '
                        'bisection from\nthe common ancestor, %s.\n')
                      % extendnode)
     else:
         # multiple possible revisions
         if good:
             ui.write(_("Due to skipped revisions, the first "
                     "good revision could be any of:\n"))
         else:
             ui.write(_("Due to skipped revisions, the first "
                     "bad revision could be any of:\n"))
         for n in nodes:
             displayer.show(repo[n])
     displayer.close()