rebase: only store collapse message once

The message is determined by the user passing --message or --log when
the rebase is started. There's no need to write it to a file for each
rebased commit; writing it once at the start of the rebase is enough.

Differential Revision: https://phab.mercurial-scm.org/D2712

hgext/rebase.py

@@ -1,1867 +1,1867
 # rebase.py - rebasing feature for mercurial
 #
 # Copyright 2008 Stefano Tortarolo <stefano.tortarolo at gmail dot com>
 #
 # This software may be used and distributed according to the terms of the
 # GNU General Public License version 2 or any later version.
 
 '''command to move sets of revisions to a different ancestor
 
 This extension lets you rebase changesets in an existing Mercurial
 repository.
 
 For more information:
 https://mercurial-scm.org/wiki/RebaseExtension
 '''
 
 from __future__ import absolute_import
 
 import errno
 import os
 
 from mercurial.i18n import _
 from mercurial.node import (
     nullid,
     nullrev,
     short,
 )
 from mercurial import (
     bookmarks,
     cmdutil,
     commands,
     copies,
     destutil,
     dirstateguard,
     error,
     extensions,
     hg,
     lock,
     merge as mergemod,
     mergeutil,
     obsolete,
     obsutil,
     patch,
     phases,
     pycompat,
     registrar,
     repair,
     revset,
     revsetlang,
     scmutil,
     smartset,
     util,
 )
 
 release = lock.release
 
 # The following constants are used throughout the rebase module. The ordering of
 # their values must be maintained.
 
 # Indicates that a revision needs to be rebased
 revtodo = -1
 revtodostr = '-1'
 
 # legacy revstates no longer needed in current code
 # -2: nullmerge, -3: revignored, -4: revprecursor, -5: revpruned
 legacystates = {'-2', '-3', '-4', '-5'}
 
 cmdtable = {}
 command = registrar.command(cmdtable)
 # Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
 # extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
 # be specifying the version(s) of Mercurial they are tested with, or
 # leave the attribute unspecified.
 testedwith = 'ships-with-hg-core'
 
 def _nothingtorebase():
     return 1
 
 def _savegraft(ctx, extra):
     s = ctx.extra().get('source', None)
     if s is not None:
         extra['source'] = s
     s = ctx.extra().get('intermediate-source', None)
     if s is not None:
         extra['intermediate-source'] = s
 
 def _savebranch(ctx, extra):
     extra['branch'] = ctx.branch()
 
 def _makeextrafn(copiers):
     """make an extrafn out of the given copy-functions.
 
     A copy function takes a context and an extra dict, and mutates the
     extra dict as needed based on the given context.
     """
     def extrafn(ctx, extra):
         for c in copiers:
             c(ctx, extra)
     return extrafn
 
 def _destrebase(repo, sourceset, destspace=None):
     """small wrapper around destmerge to pass the right extra args
 
     Please wrap destutil.destmerge instead."""
     return destutil.destmerge(repo, action='rebase', sourceset=sourceset,
                               onheadcheck=False, destspace=destspace)
 
 revsetpredicate = registrar.revsetpredicate()
 
 @revsetpredicate('_destrebase')
 def _revsetdestrebase(repo, subset, x):
     # ``_rebasedefaultdest()``
 
     # default destination for rebase.
     # # XXX: Currently private because I expect the signature to change.
     # # XXX: - bailing out in case of ambiguity vs returning all data.
     # i18n: "_rebasedefaultdest" is a keyword
     sourceset = None
     if x is not None:
         sourceset = revset.getset(repo, smartset.fullreposet(repo), x)
     return subset & smartset.baseset([_destrebase(repo, sourceset)])
 
 def _ctxdesc(ctx):
     """short description for a context"""
     desc = '%d:%s "%s"' % (ctx.rev(), ctx,
                            ctx.description().split('\n', 1)[0])
     repo = ctx.repo()
     names = []
     for nsname, ns in repo.names.iteritems():
         if nsname == 'branches':
             continue
         names.extend(ns.names(repo, ctx.node()))
     if names:
         desc += ' (%s)' % ' '.join(names)
     return desc
 
 class rebaseruntime(object):
     """This class is a container for rebase runtime state"""
     def __init__(self, repo, ui, inmemory=False, opts=None):
         if opts is None:
             opts = {}
 
         # prepared: whether we have rebasestate prepared or not. Currently it
         # decides whether "self.repo" is unfiltered or not.
         # The rebasestate has explicit hash to hash instructions not depending
         # on visibility. If rebasestate exists (in-memory or on-disk), use
         # unfiltered repo to avoid visibility issues.
         # Before knowing rebasestate (i.e. when starting a new rebase (not
         # --continue or --abort)), the original repo should be used so
         # visibility-dependent revsets are correct.
         self.prepared = False
         self._repo = repo
 
         self.ui = ui
         self.opts = opts
         self.originalwd = None
         self.external = nullrev
         # Mapping between the old revision id and either what is the new rebased
         # revision or what needs to be done with the old revision. The state
         # dict will be what contains most of the rebase progress state.
         self.state = {}
         self.activebookmark = None
         self.destmap = {}
         self.skipped = set()
 
         self.collapsef = opts.get('collapse', False)
         self.collapsemsg = cmdutil.logmessage(ui, opts)
         self.date = opts.get('date', None)
 
         e = opts.get('extrafn') # internal, used by e.g. hgsubversion
         self.extrafns = [_savegraft]
         if e:
             self.extrafns = [e]
 
         self.keepf = opts.get('keep', False)
         self.keepbranchesf = opts.get('keepbranches', False)
         self.obsoletenotrebased = {}
         self.obsoletewithoutsuccessorindestination = set()
         self.inmemory = inmemory
 
     @property
     def repo(self):
         if self.prepared:
             return self._repo.unfiltered()
         else:
             return self._repo
 
     def storestatus(self, tr=None):
         """Store the current status to allow recovery"""
         if tr:
             tr.addfilegenerator('rebasestate', ('rebasestate',),
                                 self._writestatus, location='plain')
         else:
             with self.repo.vfs("rebasestate", "w") as f:
                 self._writestatus(f)
 
     def _writestatus(self, f):
         repo = self.repo
         assert repo.filtername is None
         f.write(repo[self.originalwd].hex() + '\n')
         # was "dest". we now write dest per src root below.
         f.write('\n')
         f.write(repo[self.external].hex() + '\n')
         f.write('%d\n' % int(self.collapsef))
         f.write('%d\n' % int(self.keepf))
         f.write('%d\n' % int(self.keepbranchesf))
         f.write('%s\n' % (self.activebookmark or ''))
         destmap = self.destmap
         for d, v in self.state.iteritems():
             oldrev = repo[d].hex()
             if v >= 0:
                 newrev = repo[v].hex()
             else:
                 newrev = "%d" % v
             destnode = repo[destmap[d]].hex()
             f.write("%s:%s:%s\n" % (oldrev, newrev, destnode))
         repo.ui.debug('rebase status stored\n')
 
     def restorestatus(self):
         """Restore a previously stored status"""
         self.prepared = True
         repo = self.repo
         assert repo.filtername is None
         keepbranches = None
         legacydest = None
         collapse = False
         external = nullrev
         activebookmark = None
         state = {}
         destmap = {}
 
         try:
             f = repo.vfs("rebasestate")
             for i, l in enumerate(f.read().splitlines()):
                 if i == 0:
                     originalwd = repo[l].rev()
                 elif i == 1:
                     # this line should be empty in newer version. but legacy
                     # clients may still use it
                     if l:
                         legacydest = repo[l].rev()
                 elif i == 2:
                     external = repo[l].rev()
                 elif i == 3:
                     collapse = bool(int(l))
                 elif i == 4:
                     keep = bool(int(l))
                 elif i == 5:
                     keepbranches = bool(int(l))
                 elif i == 6 and not (len(l) == 81 and ':' in l):
                     # line 6 is a recent addition, so for backwards
                     # compatibility check that the line doesn't look like the
                     # oldrev:newrev lines
                     activebookmark = l
                 else:
                     args = l.split(':')
                     oldrev = args[0]
                     newrev = args[1]
                     if newrev in legacystates:
                         continue
                     if len(args) > 2:
                         destnode = args[2]
                     else:
                         destnode = legacydest
                     destmap[repo[oldrev].rev()] = repo[destnode].rev()
                     if newrev in (nullid, revtodostr):
                         state[repo[oldrev].rev()] = revtodo
                         # Legacy compat special case
                     else:
                         state[repo[oldrev].rev()] = repo[newrev].rev()
 
         except IOError as err:
             if err.errno != errno.ENOENT:
                 raise
             cmdutil.wrongtooltocontinue(repo, _('rebase'))
 
         if keepbranches is None:
             raise error.Abort(_('.hg/rebasestate is incomplete'))
 
         skipped = set()
         # recompute the set of skipped revs
         if not collapse:
             seen = set(destmap.values())
             for old, new in sorted(state.items()):
                 if new != revtodo and new in seen:
                     skipped.add(old)
                 seen.add(new)
         repo.ui.debug('computed skipped revs: %s\n' %
                         (' '.join('%d' % r for r in sorted(skipped)) or ''))
         repo.ui.debug('rebase status resumed\n')
 
         self.originalwd = originalwd
         self.destmap = destmap
         self.state = state
         self.skipped = skipped
         self.collapsef = collapse
         self.keepf = keep
         self.keepbranchesf = keepbranches
         self.external = external
         self.activebookmark = activebookmark
 
     def _handleskippingobsolete(self, obsoleterevs, destmap):
         """Compute structures necessary for skipping obsolete revisions
 
         obsoleterevs:   iterable of all obsolete revisions in rebaseset
         destmap:        {srcrev: destrev} destination revisions
         """
         self.obsoletenotrebased = {}
         if not self.ui.configbool('experimental', 'rebaseskipobsolete'):
             return
         obsoleteset = set(obsoleterevs)
         (self.obsoletenotrebased,
          self.obsoletewithoutsuccessorindestination,
          obsoleteextinctsuccessors) = _computeobsoletenotrebased(
              self.repo, obsoleteset, destmap)
         skippedset = set(self.obsoletenotrebased)
         skippedset.update(self.obsoletewithoutsuccessorindestination)
         skippedset.update(obsoleteextinctsuccessors)
         _checkobsrebase(self.repo, self.ui, obsoleteset, skippedset)
 
     def _prepareabortorcontinue(self, isabort):
         try:
             self.restorestatus()
             self.collapsemsg = restorecollapsemsg(self.repo, isabort)
         except error.RepoLookupError:
             if isabort:
                 clearstatus(self.repo)
                 clearcollapsemsg(self.repo)
                 self.repo.ui.warn(_('rebase aborted (no revision is removed,'
                                     ' only broken state is cleared)\n'))
                 return 0
             else:
                 msg = _('cannot continue inconsistent rebase')
                 hint = _('use "hg rebase --abort" to clear broken state')
                 raise error.Abort(msg, hint=hint)
         if isabort:
             return abort(self.repo, self.originalwd, self.destmap,
                          self.state, activebookmark=self.activebookmark)
 
     def _preparenewrebase(self, destmap):
         if not destmap:
             return _nothingtorebase()
 
         rebaseset = destmap.keys()
         allowunstable = obsolete.isenabled(self.repo, obsolete.allowunstableopt)
         if (not (self.keepf or allowunstable)
               and self.repo.revs('first(children(%ld) - %ld)',
                                  rebaseset, rebaseset)):
             raise error.Abort(
                 _("can't remove original changesets with"
                   " unrebased descendants"),
                 hint=_('use --keep to keep original changesets'))
 
         result = buildstate(self.repo, destmap, self.collapsef)
 
         if not result:
             # Empty state built, nothing to rebase
             self.ui.status(_('nothing to rebase\n'))
             return _nothingtorebase()
 
         for root in self.repo.set('roots(%ld)', rebaseset):
             if not self.keepf and not root.mutable():
                 raise error.Abort(_("can't rebase public changeset %s")
                                   % root,
                                   hint=_("see 'hg help phases' for details"))
 
         (self.originalwd, self.destmap, self.state) = result
         if self.collapsef:
             dests = set(self.destmap.values())
             if len(dests) != 1:
                 raise error.Abort(
                     _('--collapse does not work with multiple destinations'))
             destrev = next(iter(dests))
             destancestors = self.repo.changelog.ancestors([destrev],
                                                           inclusive=True)
             self.external = externalparent(self.repo, self.state, destancestors)
 
         for destrev in sorted(set(destmap.values())):
             dest = self.repo[destrev]
             if dest.closesbranch() and not self.keepbranchesf:
                 self.ui.status(_('reopening closed branch head %s\n') % dest)
 
         self.prepared = True
 
     def _assignworkingcopy(self):
         if self.inmemory:
             from mercurial.context import overlayworkingctx
             self.wctx = overlayworkingctx(self.repo)
             self.repo.ui.debug("rebasing in-memory\n")
         else:
             self.wctx = self.repo[None]
             self.repo.ui.debug("rebasing on disk\n")
         self.repo.ui.log("rebase", "", rebase_imm_used=self.wctx.isinmemory())
 
     def _performrebase(self, tr):
         self._assignworkingcopy()
         repo, ui = self.repo, self.ui
         if self.keepbranchesf:
             # insert _savebranch at the start of extrafns so if
             # there's a user-provided extrafn it can clobber branch if
             # desired
             self.extrafns.insert(0, _savebranch)
             if self.collapsef:
                 branches = set()
                 for rev in self.state:
                     branches.add(repo[rev].branch())
                     if len(branches) > 1:
                         raise error.Abort(_('cannot collapse multiple named '
                             'branches'))
 
         # Calculate self.obsoletenotrebased
         obsrevs = _filterobsoleterevs(self.repo, self.state)
         self._handleskippingobsolete(obsrevs, self.destmap)
 
         # Keep track of the active bookmarks in order to reset them later
         self.activebookmark = self.activebookmark or repo._activebookmark
         if self.activebookmark:
             bookmarks.deactivate(repo)
 
         # Store the state before we begin so users can run 'hg rebase --abort'
         # if we fail before the transaction closes.
         self.storestatus()
 
         cands = [k for k, v in self.state.iteritems() if v == revtodo]
         total = len(cands)
         pos = 0
         for subset in sortsource(self.destmap):
             pos = self._performrebasesubset(tr, subset, pos, total)
         ui.progress(_('rebasing'), None)
         ui.note(_('rebase merging completed\n'))
 
     def _performrebasesubset(self, tr, subset, pos, total):
         repo, ui, opts = self.repo, self.ui, self.opts
         sortedrevs = repo.revs('sort(%ld, -topo)', subset)
         allowdivergence = self.ui.configbool(
             'experimental', 'evolution.allowdivergence')
         if not allowdivergence:
             sortedrevs -= repo.revs(
                 'descendants(%ld) and not %ld',
                 self.obsoletewithoutsuccessorindestination,
                 self.obsoletewithoutsuccessorindestination,
             )
         for rev in sortedrevs:
             dest = self.destmap[rev]
             ctx = repo[rev]
             desc = _ctxdesc(ctx)
             if self.state[rev] == rev:
                 ui.status(_('already rebased %s\n') % desc)
             elif (not allowdivergence
                   and rev in self.obsoletewithoutsuccessorindestination):
                 msg = _('note: not rebasing %s and its descendants as '
                         'this would cause divergence\n') % desc
                 repo.ui.status(msg)
                 self.skipped.add(rev)
             elif rev in self.obsoletenotrebased:
                 succ = self.obsoletenotrebased[rev]
                 if succ is None:
                     msg = _('note: not rebasing %s, it has no '
                             'successor\n') % desc
                 else:
                     succdesc = _ctxdesc(repo[succ])
                     msg = (_('note: not rebasing %s, already in '
                              'destination as %s\n') % (desc, succdesc))
                 repo.ui.status(msg)
                 # Make clearrebased aware state[rev] is not a true successor
                 self.skipped.add(rev)
                 # Record rev as moved to its desired destination in self.state.
                 # This helps bookmark and working parent movement.
                 dest = max(adjustdest(repo, rev, self.destmap, self.state,
                                       self.skipped))
                 self.state[rev] = dest
             elif self.state[rev] == revtodo:
                 pos += 1
                 ui.status(_('rebasing %s\n') % desc)
                 ui.progress(_("rebasing"), pos, ("%d:%s" % (rev, ctx)),
                             _('changesets'), total)
                 p1, p2, base = defineparents(repo, rev, self.destmap,
                                              self.state, self.skipped,
                                              self.obsoletenotrebased)
                 self.storestatus(tr=tr)
-                storecollapsemsg(repo, self.collapsemsg)
                 if len(repo[None].parents()) == 2:
                     repo.ui.debug('resuming interrupted rebase\n')
                 else:
                     try:
                         ui.setconfig('ui', 'forcemerge', opts.get('tool', ''),
                                      'rebase')
                         stats = rebasenode(repo, rev, p1, base, self.collapsef,
                                            dest, wctx=self.wctx)
                         if stats and stats[3] > 0:
                             if self.wctx.isinmemory():
                                 raise error.InMemoryMergeConflictsError()
                             else:
                                 raise error.InterventionRequired(
                                     _('unresolved conflicts (see hg '
                                       'resolve, then hg rebase --continue)'))
                     finally:
                         ui.setconfig('ui', 'forcemerge', '', 'rebase')
                 if not self.collapsef:
                     merging = p2 != nullrev
                     editform = cmdutil.mergeeditform(merging, 'rebase')
                     editor = cmdutil.getcommiteditor(editform=editform,
                                                      **pycompat.strkwargs(opts))
                     if self.wctx.isinmemory():
                         newnode = concludememorynode(repo, rev, p1, p2,
                             wctx=self.wctx,
                             extrafn=_makeextrafn(self.extrafns),
                             editor=editor,
                             keepbranches=self.keepbranchesf,
                             date=self.date)
                         mergemod.mergestate.clean(repo)
                     else:
                         newnode = concludenode(repo, rev, p1, p2,
                             extrafn=_makeextrafn(self.extrafns),
                             editor=editor,
                             keepbranches=self.keepbranchesf,
                             date=self.date)
 
                     if newnode is None:
                         # If it ended up being a no-op commit, then the normal
                         # merge state clean-up path doesn't happen, so do it
                         # here. Fix issue5494
                         mergemod.mergestate.clean(repo)
                 else:
                     # Skip commit if we are collapsing
                     if self.wctx.isinmemory():
                         self.wctx.setbase(repo[p1])
                     else:
                         repo.setparents(repo[p1].node())
                     newnode = None
                 # Update the state
                 if newnode is not None:
                     self.state[rev] = repo[newnode].rev()
                     ui.debug('rebased as %s\n' % short(newnode))
                 else:
                     if not self.collapsef:
                         ui.warn(_('note: rebase of %d:%s created no changes '
                                   'to commit\n') % (rev, ctx))
                         self.skipped.add(rev)
                     self.state[rev] = p1
                     ui.debug('next revision set to %d\n' % p1)
             else:
                 ui.status(_('already rebased %s as %s\n') %
                           (desc, repo[self.state[rev]]))
         return pos
 
     def _finishrebase(self):
         repo, ui, opts = self.repo, self.ui, self.opts
         fm = ui.formatter('rebase', opts)
         fm.startitem()
         if self.collapsef:
             p1, p2, _base = defineparents(repo, min(self.state), self.destmap,
                                           self.state, self.skipped,
                                           self.obsoletenotrebased)
             editopt = opts.get('edit')
             editform = 'rebase.collapse'
             if self.collapsemsg:
                 commitmsg = self.collapsemsg
             else:
                 commitmsg = 'Collapsed revision'
                 for rebased in sorted(self.state):
                     if rebased not in self.skipped:
                         commitmsg += '\n* %s' % repo[rebased].description()
                 editopt = True
             editor = cmdutil.getcommiteditor(edit=editopt, editform=editform)
             revtoreuse = max(self.state)
 
             if self.inmemory:
                 newnode = concludememorynode(repo, revtoreuse, p1,
                     self.external,
                     commitmsg=commitmsg,
                     extrafn=_makeextrafn(self.extrafns),
                     editor=editor,
                     keepbranches=self.keepbranchesf,
                     date=self.date, wctx=self.wctx)
             else:
                 dsguard = None
                 if ui.configbool('rebase', 'singletransaction'):
                     dsguard = dirstateguard.dirstateguard(repo, 'rebase')
                 with util.acceptintervention(dsguard):
                     newnode = concludenode(repo, revtoreuse, p1, self.external,
                         commitmsg=commitmsg,
                         extrafn=_makeextrafn(self.extrafns),
                         editor=editor,
                         keepbranches=self.keepbranchesf,
                         date=self.date)
             if newnode is not None:
                 newrev = repo[newnode].rev()
                 for oldrev in self.state:
                     self.state[oldrev] = newrev
 
         if 'qtip' in repo.tags():
             updatemq(repo, self.state, self.skipped,
                      **pycompat.strkwargs(opts))
 
         # restore original working directory
         # (we do this before stripping)
         newwd = self.state.get(self.originalwd, self.originalwd)
         if newwd < 0:
             # original directory is a parent of rebase set root or ignored
             newwd = self.originalwd
         if (newwd not in [c.rev() for c in repo[None].parents()] and
                 not self.inmemory):
             ui.note(_("update back to initial working directory parent\n"))
             hg.updaterepo(repo, newwd, False)
 
         collapsedas = None
         if self.collapsef and not self.keepf:
             collapsedas = newnode
         clearrebased(ui, repo, self.destmap, self.state, self.skipped,
                      collapsedas, self.keepf, fm=fm)
 
         clearstatus(repo)
         clearcollapsemsg(repo)
 
         ui.note(_("rebase completed\n"))
         util.unlinkpath(repo.sjoin('undo'), ignoremissing=True)
         if self.skipped:
             skippedlen = len(self.skipped)
             ui.note(_("%d revisions have been skipped\n") % skippedlen)
         fm.end()
 
         if (self.activebookmark and self.activebookmark in repo._bookmarks and
             repo['.'].node() == repo._bookmarks[self.activebookmark]):
                 bookmarks.activate(repo, self.activebookmark)
 
 @command('rebase',
     [('s', 'source', '',
      _('rebase the specified changeset and descendants'), _('REV')),
     ('b', 'base', '',
      _('rebase everything from branching point of specified changeset'),
      _('REV')),
     ('r', 'rev', [],
      _('rebase these revisions'),
      _('REV')),
     ('d', 'dest', '',
      _('rebase onto the specified changeset'), _('REV')),
     ('', 'collapse', False, _('collapse the rebased changesets')),
     ('m', 'message', '',
      _('use text as collapse commit message'), _('TEXT')),
     ('e', 'edit', False, _('invoke editor on commit messages')),
     ('l', 'logfile', '',
      _('read collapse commit message from file'), _('FILE')),
     ('k', 'keep', False, _('keep original changesets')),
     ('', 'keepbranches', False, _('keep original branch names')),
     ('D', 'detach', False, _('(DEPRECATED)')),
     ('i', 'interactive', False, _('(DEPRECATED)')),
     ('t', 'tool', '', _('specify merge tool')),
     ('c', 'continue', False, _('continue an interrupted rebase')),
     ('a', 'abort', False, _('abort an interrupted rebase'))] +
     cmdutil.formatteropts,
     _('[-s REV | -b REV] [-d REV] [OPTION]'))
 def rebase(ui, repo, **opts):
     """move changeset (and descendants) to a different branch
 
     Rebase uses repeated merging to graft changesets from one part of
     history (the source) onto another (the destination). This can be
     useful for linearizing *local* changes relative to a master
     development tree.
 
     Published commits cannot be rebased (see :hg:`help phases`).
     To copy commits, see :hg:`help graft`.
 
     If you don't specify a destination changeset (``-d/--dest``), rebase
     will use the same logic as :hg:`merge` to pick a destination.  if
     the current branch contains exactly one other head, the other head
     is merged with by default.  Otherwise, an explicit revision with
     which to merge with must be provided.  (destination changeset is not
     modified by rebasing, but new changesets are added as its
     descendants.)
 
     Here are the ways to select changesets:
 
       1. Explicitly select them using ``--rev``.
 
       2. Use ``--source`` to select a root changeset and include all of its
          descendants.
 
       3. Use ``--base`` to select a changeset; rebase will find ancestors
          and their descendants which are not also ancestors of the destination.
 
       4. If you do not specify any of ``--rev``, ``source``, or ``--base``,
          rebase will use ``--base .`` as above.
 
     If ``--source`` or ``--rev`` is used, special names ``SRC`` and ``ALLSRC``
     can be used in ``--dest``. Destination would be calculated per source
     revision with ``SRC`` substituted by that single source revision and
     ``ALLSRC`` substituted by all source revisions.
 
     Rebase will destroy original changesets unless you use ``--keep``.
     It will also move your bookmarks (even if you do).
 
     Some changesets may be dropped if they do not contribute changes
     (e.g. merges from the destination branch).
 
     Unlike ``merge``, rebase will do nothing if you are at the branch tip of
     a named branch with two heads. You will need to explicitly specify source
     and/or destination.
 
     If you need to use a tool to automate merge/conflict decisions, you
     can specify one with ``--tool``, see :hg:`help merge-tools`.
     As a caveat: the tool will not be used to mediate when a file was
     deleted, there is no hook presently available for this.
 
     If a rebase is interrupted to manually resolve a conflict, it can be
     continued with --continue/-c or aborted with --abort/-a.
 
     .. container:: verbose
 
       Examples:
 
       - move "local changes" (current commit back to branching point)
         to the current branch tip after a pull::
 
           hg rebase
 
       - move a single changeset to the stable branch::
 
           hg rebase -r 5f493448 -d stable
 
       - splice a commit and all its descendants onto another part of history::
 
           hg rebase --source c0c3 --dest 4cf9
 
       - rebase everything on a branch marked by a bookmark onto the
         default branch::
 
           hg rebase --base myfeature --dest default
 
       - collapse a sequence of changes into a single commit::
 
           hg rebase --collapse -r 1520:1525 -d .
 
       - move a named branch while preserving its name::
 
           hg rebase -r "branch(featureX)" -d 1.3 --keepbranches
 
       - stabilize orphaned changesets so history looks linear::
 
           hg rebase -r 'orphan()-obsolete()'\
  -d 'first(max((successors(max(roots(ALLSRC) & ::SRC)^)-obsolete())::) +\
  max(::((roots(ALLSRC) & ::SRC)^)-obsolete()))'
 
     Configuration Options:
 
     You can make rebase require a destination if you set the following config
     option::
 
       [commands]
       rebase.requiredest = True
 
     By default, rebase will close the transaction after each commit. For
     performance purposes, you can configure rebase to use a single transaction
     across the entire rebase. WARNING: This setting introduces a significant
     risk of losing the work you've done in a rebase if the rebase aborts
     unexpectedly::
 
       [rebase]
       singletransaction = True
 
     By default, rebase writes to the working copy, but you can configure it to
     run in-memory for for better performance, and to allow it to run if the
     working copy is dirty::
 
       [rebase]
       experimental.inmemory = True
 
     Return Values:
 
     Returns 0 on success, 1 if nothing to rebase or there are
     unresolved conflicts.
 
     """
     inmemory = ui.configbool('rebase', 'experimental.inmemory')
     if (opts.get('continue') or opts.get('abort') or
         repo.currenttransaction() is not None):
         # in-memory rebase is not compatible with resuming rebases.
         # (Or if it is run within a transaction, since the restart logic can
         # fail the entire transaction.)
         inmemory = False
 
     if inmemory:
         try:
             # in-memory merge doesn't support conflicts, so if we hit any, abort
             # and re-run as an on-disk merge.
             return _origrebase(ui, repo, inmemory=inmemory, **opts)
         except error.InMemoryMergeConflictsError:
             ui.warn(_('hit merge conflicts; re-running rebase without in-memory'
                       ' merge\n'))
             _origrebase(ui, repo, **{'abort': True})
             return _origrebase(ui, repo, inmemory=False, **opts)
     else:
         return _origrebase(ui, repo, **opts)
 
 def _origrebase(ui, repo, inmemory=False, **opts):
     opts = pycompat.byteskwargs(opts)
     rbsrt = rebaseruntime(repo, ui, inmemory, opts)
 
     with repo.wlock(), repo.lock():
         # Validate input and define rebasing points
         destf = opts.get('dest', None)
         srcf = opts.get('source', None)
         basef = opts.get('base', None)
         revf = opts.get('rev', [])
         # search default destination in this space
         # used in the 'hg pull --rebase' case, see issue 5214.
         destspace = opts.get('_destspace')
         contf = opts.get('continue')
         abortf = opts.get('abort')
         if opts.get('interactive'):
             try:
                 if extensions.find('histedit'):
                     enablehistedit = ''
             except KeyError:
                 enablehistedit = " --config extensions.histedit="
             help = "hg%s help -e histedit" % enablehistedit
             msg = _("interactive history editing is supported by the "
                     "'histedit' extension (see \"%s\")") % help
             raise error.Abort(msg)
 
         if rbsrt.collapsemsg and not rbsrt.collapsef:
             raise error.Abort(
                 _('message can only be specified with collapse'))
 
         if contf or abortf:
             if contf and abortf:
                 raise error.Abort(_('cannot use both abort and continue'))
             if rbsrt.collapsef:
                 raise error.Abort(
                     _('cannot use collapse with continue or abort'))
             if srcf or basef or destf:
                 raise error.Abort(
                     _('abort and continue do not allow specifying revisions'))
             if abortf and opts.get('tool', False):
                 ui.warn(_('tool option will be ignored\n'))
             if contf:
                 ms = mergemod.mergestate.read(repo)
                 mergeutil.checkunresolved(ms)
 
             retcode = rbsrt._prepareabortorcontinue(abortf)
             if retcode is not None:
                 return retcode
         else:
             destmap = _definedestmap(ui, repo, rbsrt, destf, srcf, basef, revf,
                                      destspace=destspace)
             retcode = rbsrt._preparenewrebase(destmap)
             if retcode is not None:
                 return retcode
+            storecollapsemsg(repo, rbsrt.collapsemsg)
 
         tr = None
 
         singletr = ui.configbool('rebase', 'singletransaction')
         if singletr:
             tr = repo.transaction('rebase')
 
         # If `rebase.singletransaction` is enabled, wrap the entire operation in
         # one transaction here. Otherwise, transactions are obtained when
         # committing each node, which is slower but allows partial success.
         with util.acceptintervention(tr):
             # Same logic for the dirstate guard, except we don't create one when
             # rebasing in-memory (it's not needed).
             dsguard = None
             if singletr and not inmemory:
                 dsguard = dirstateguard.dirstateguard(repo, 'rebase')
             with util.acceptintervention(dsguard):
                 rbsrt._performrebase(tr)
 
         rbsrt._finishrebase()
 
 def _definedestmap(ui, repo, rbsrt, destf=None, srcf=None, basef=None,
                    revf=None, destspace=None):
     """use revisions argument to define destmap {srcrev: destrev}"""
     if revf is None:
         revf = []
 
     # destspace is here to work around issues with `hg pull --rebase` see
     # issue5214 for details
     if srcf and basef:
         raise error.Abort(_('cannot specify both a source and a base'))
     if revf and basef:
         raise error.Abort(_('cannot specify both a revision and a base'))
     if revf and srcf:
         raise error.Abort(_('cannot specify both a revision and a source'))
 
     if not rbsrt.inmemory:
         cmdutil.checkunfinished(repo)
         cmdutil.bailifchanged(repo)
 
     if ui.configbool('commands', 'rebase.requiredest') and not destf:
         raise error.Abort(_('you must specify a destination'),
                           hint=_('use: hg rebase -d REV'))
 
     dest = None
 
     if revf:
         rebaseset = scmutil.revrange(repo, revf)
         if not rebaseset:
             ui.status(_('empty "rev" revision set - nothing to rebase\n'))
             return None
     elif srcf:
         src = scmutil.revrange(repo, [srcf])
         if not src:
             ui.status(_('empty "source" revision set - nothing to rebase\n'))
             return None
         rebaseset = repo.revs('(%ld)::', src)
         assert rebaseset
     else:
         base = scmutil.revrange(repo, [basef or '.'])
         if not base:
             ui.status(_('empty "base" revision set - '
                         "can't compute rebase set\n"))
             return None
         if destf:
             # --base does not support multiple destinations
             dest = scmutil.revsingle(repo, destf)
         else:
             dest = repo[_destrebase(repo, base, destspace=destspace)]
             destf = bytes(dest)
 
         roots = [] # selected children of branching points
         bpbase = {} # {branchingpoint: [origbase]}
         for b in base: # group bases by branching points
             bp = repo.revs('ancestor(%d, %d)', b, dest.rev()).first()
             bpbase[bp] = bpbase.get(bp, []) + [b]
         if None in bpbase:
             # emulate the old behavior, showing "nothing to rebase" (a better
             # behavior may be abort with "cannot find branching point" error)
             bpbase.clear()
         for bp, bs in bpbase.iteritems(): # calculate roots
             roots += list(repo.revs('children(%d) & ancestors(%ld)', bp, bs))
 
         rebaseset = repo.revs('%ld::', roots)
 
         if not rebaseset:
             # transform to list because smartsets are not comparable to
             # lists. This should be improved to honor laziness of
             # smartset.
             if list(base) == [dest.rev()]:
                 if basef:
                     ui.status(_('nothing to rebase - %s is both "base"'
                                 ' and destination\n') % dest)
                 else:
                     ui.status(_('nothing to rebase - working directory '
                                 'parent is also destination\n'))
             elif not repo.revs('%ld - ::%d', base, dest.rev()):
                 if basef:
                     ui.status(_('nothing to rebase - "base" %s is '
                                 'already an ancestor of destination '
                                 '%s\n') %
                               ('+'.join(bytes(repo[r]) for r in base),
                                dest))
                 else:
                     ui.status(_('nothing to rebase - working '
                                 'directory parent is already an '
                                 'ancestor of destination %s\n') % dest)
             else: # can it happen?
                 ui.status(_('nothing to rebase from %s to %s\n') %
                           ('+'.join(bytes(repo[r]) for r in base), dest))
             return None
     # If rebasing the working copy parent, force in-memory merge to be off.
     #
     # This is because the extra work of checking out the newly rebased commit
     # outweights the benefits of rebasing in-memory, and executing an extra
     # update command adds a bit of overhead, so better to just do it on disk. In
     # all other cases leave it on.
     #
     # Note that there are cases where this isn't true -- e.g., rebasing large
     # stacks that include the WCP. However, I'm not yet sure where the cutoff
     # is.
     rebasingwcp = repo['.'].rev() in rebaseset
     ui.log("rebase", "", rebase_rebasing_wcp=rebasingwcp)
     if rbsrt.inmemory and rebasingwcp:
         rbsrt.inmemory = False
         # Check these since we did not before.
         cmdutil.checkunfinished(repo)
         cmdutil.bailifchanged(repo)
 
     if not destf:
         dest = repo[_destrebase(repo, rebaseset, destspace=destspace)]
         destf = bytes(dest)
 
     allsrc = revsetlang.formatspec('%ld', rebaseset)
     alias = {'ALLSRC': allsrc}
 
     if dest is None:
         try:
             # fast path: try to resolve dest without SRC alias
             dest = scmutil.revsingle(repo, destf, localalias=alias)
         except error.RepoLookupError:
             # multi-dest path: resolve dest for each SRC separately
             destmap = {}
             for r in rebaseset:
                 alias['SRC'] = revsetlang.formatspec('%d', r)
                 # use repo.anyrevs instead of scmutil.revsingle because we
                 # don't want to abort if destset is empty.
                 destset = repo.anyrevs([destf], user=True, localalias=alias)
                 size = len(destset)
                 if size == 1:
                     destmap[r] = destset.first()
                 elif size == 0:
                     ui.note(_('skipping %s - empty destination\n') % repo[r])
                 else:
                     raise error.Abort(_('rebase destination for %s is not '
                                         'unique') % repo[r])
 
     if dest is not None:
         # single-dest case: assign dest to each rev in rebaseset
         destrev = dest.rev()
         destmap = {r: destrev for r in rebaseset} # {srcrev: destrev}
 
     if not destmap:
         ui.status(_('nothing to rebase - empty destination\n'))
         return None
 
     return destmap
 
 def externalparent(repo, state, destancestors):
     """Return the revision that should be used as the second parent
     when the revisions in state is collapsed on top of destancestors.
     Abort if there is more than one parent.
     """
     parents = set()
     source = min(state)
     for rev in state:
         if rev == source:
             continue
         for p in repo[rev].parents():
             if (p.rev() not in state
                         and p.rev() not in destancestors):
                 parents.add(p.rev())
     if not parents:
         return nullrev
     if len(parents) == 1:
         return parents.pop()
     raise error.Abort(_('unable to collapse on top of %d, there is more '
                        'than one external parent: %s') %
                      (max(destancestors),
                       ', '.join("%d" % p for p in sorted(parents))))
 
 def concludememorynode(repo, rev, p1, p2, wctx=None,
                        commitmsg=None, editor=None, extrafn=None,
                        keepbranches=False, date=None):
     '''Commit the memory changes with parents p1 and p2. Reuse commit info from
     rev but also store useful information in extra.
     Return node of committed revision.'''
     ctx = repo[rev]
     if commitmsg is None:
         commitmsg = ctx.description()
     keepbranch = keepbranches and repo[p1].branch() != ctx.branch()
     extra = {'rebase_source': ctx.hex()}
     if extrafn:
         extrafn(ctx, extra)
 
     destphase = max(ctx.phase(), phases.draft)
     overrides = {('phases', 'new-commit'): destphase}
     with repo.ui.configoverride(overrides, 'rebase'):
         if keepbranch:
             repo.ui.setconfig('ui', 'allowemptycommit', True)
         # Replicates the empty check in ``repo.commit``.
         if wctx.isempty() and not repo.ui.configbool('ui', 'allowemptycommit'):
             return None
 
         if date is None:
             date = ctx.date()
 
         # By convention, ``extra['branch']`` (set by extrafn) clobbers
         # ``branch`` (used when passing ``--keepbranches``).
         branch = repo[p1].branch()
         if 'branch' in extra:
             branch = extra['branch']
 
         memctx = wctx.tomemctx(commitmsg, parents=(p1, p2), date=date,
             extra=extra, user=ctx.user(), branch=branch, editor=editor)
         commitres = repo.commitctx(memctx)
         wctx.clean() # Might be reused
         return commitres
 
 def concludenode(repo, rev, p1, p2, commitmsg=None, editor=None, extrafn=None,
                  keepbranches=False, date=None):
     '''Commit the wd changes with parents p1 and p2. Reuse commit info from rev
     but also store useful information in extra.
     Return node of committed revision.'''
     dsguard = util.nullcontextmanager()
     if not repo.ui.configbool('rebase', 'singletransaction'):
         dsguard = dirstateguard.dirstateguard(repo, 'rebase')
     with dsguard:
         repo.setparents(repo[p1].node(), repo[p2].node())
         ctx = repo[rev]
         if commitmsg is None:
             commitmsg = ctx.description()
         keepbranch = keepbranches and repo[p1].branch() != ctx.branch()
         extra = {'rebase_source': ctx.hex()}
         if extrafn:
             extrafn(ctx, extra)
 
         destphase = max(ctx.phase(), phases.draft)
         overrides = {('phases', 'new-commit'): destphase}
         with repo.ui.configoverride(overrides, 'rebase'):
             if keepbranch:
                 repo.ui.setconfig('ui', 'allowemptycommit', True)
             # Commit might fail if unresolved files exist
             if date is None:
                 date = ctx.date()
             newnode = repo.commit(text=commitmsg, user=ctx.user(),
                                   date=date, extra=extra, editor=editor)
 
         repo.dirstate.setbranch(repo[newnode].branch())
         return newnode
 
 def rebasenode(repo, rev, p1, base, collapse, dest, wctx):
     'Rebase a single revision rev on top of p1 using base as merge ancestor'
     # Merge phase
     # Update to destination and merge it with local
     if wctx.isinmemory():
         wctx.setbase(repo[p1])
     else:
         if repo['.'].rev() != p1:
             repo.ui.debug(" update to %d:%s\n" % (p1, repo[p1]))
             mergemod.update(repo, p1, False, True)
         else:
             repo.ui.debug(" already in destination\n")
         # This is, alas, necessary to invalidate workingctx's manifest cache,
         # as well as other data we litter on it in other places.
         wctx = repo[None]
         repo.dirstate.write(repo.currenttransaction())
     repo.ui.debug(" merge against %d:%s\n" % (rev, repo[rev]))
     if base is not None:
         repo.ui.debug("   detach base %d:%s\n" % (base, repo[base]))
     # When collapsing in-place, the parent is the common ancestor, we
     # have to allow merging with it.
     stats = mergemod.update(repo, rev, True, True, base, collapse,
                             labels=['dest', 'source'], wc=wctx)
     if collapse:
         copies.duplicatecopies(repo, wctx, rev, dest)
     else:
         # If we're not using --collapse, we need to
         # duplicate copies between the revision we're
         # rebasing and its first parent, but *not*
         # duplicate any copies that have already been
         # performed in the destination.
         p1rev = repo[rev].p1().rev()
         copies.duplicatecopies(repo, wctx, rev, p1rev, skiprev=dest)
     return stats
 
 def adjustdest(repo, rev, destmap, state, skipped):
     """adjust rebase destination given the current rebase state
 
     rev is what is being rebased. Return a list of two revs, which are the
     adjusted destinations for rev's p1 and p2, respectively. If a parent is
     nullrev, return dest without adjustment for it.
 
     For example, when doing rebasing B+E to F, C to G, rebase will first move B
     to B1, and E's destination will be adjusted from F to B1.
 
         B1 <- written during rebasing B
         |
         F <- original destination of B, E
         |
         | E <- rev, which is being rebased
         | |
         | D <- prev, one parent of rev being checked
         | |
         | x <- skipped, ex. no successor or successor in (::dest)
         | |
         | C <- rebased as C', different destination
         | |
         | B <- rebased as B1     C'
         |/                       |
         A                        G <- destination of C, different
 
     Another example about merge changeset, rebase -r C+G+H -d K, rebase will
     first move C to C1, G to G1, and when it's checking H, the adjusted
     destinations will be [C1, G1].
 
             H       C1 G1
            /|       | /
           F G       |/
         K | |  ->   K
         | C D       |
         | |/        |
         | B         | ...
         |/          |/
         A           A
 
     Besides, adjust dest according to existing rebase information. For example,
 
       B C D    B needs to be rebased on top of C, C needs to be rebased on top
        \|/     of D. We will rebase C first.
         A
 
           C'   After rebasing C, when considering B's destination, use C'
           |    instead of the original C.
       B   D
        \ /
         A
     """
     # pick already rebased revs with same dest from state as interesting source
     dest = destmap[rev]
     source = [s for s, d in state.items()
               if d > 0 and destmap[s] == dest and s not in skipped]
 
     result = []
     for prev in repo.changelog.parentrevs(rev):
         adjusted = dest
         if prev != nullrev:
             candidate = repo.revs('max(%ld and (::%d))', source, prev).first()
             if candidate is not None:
                 adjusted = state[candidate]
         if adjusted == dest and dest in state:
             adjusted = state[dest]
             if adjusted == revtodo:
                 # sortsource should produce an order that makes this impossible
                 raise error.ProgrammingError(
                     'rev %d should be rebased already at this time' % dest)
         result.append(adjusted)
     return result
 
 def _checkobsrebase(repo, ui, rebaseobsrevs, rebaseobsskipped):
     """
     Abort if rebase will create divergence or rebase is noop because of markers
 
     `rebaseobsrevs`: set of obsolete revision in source
     `rebaseobsskipped`: set of revisions from source skipped because they have
     successors in destination or no non-obsolete successor.
     """
     # Obsolete node with successors not in dest leads to divergence
     divergenceok = ui.configbool('experimental',
                                  'evolution.allowdivergence')
     divergencebasecandidates = rebaseobsrevs - rebaseobsskipped
 
     if divergencebasecandidates and not divergenceok:
         divhashes = (bytes(repo[r])
                      for r in divergencebasecandidates)
         msg = _("this rebase will cause "
                 "divergences from: %s")
         h = _("to force the rebase please set "
               "experimental.evolution.allowdivergence=True")
         raise error.Abort(msg % (",".join(divhashes),), hint=h)
 
 def successorrevs(unfi, rev):
     """yield revision numbers for successors of rev"""
     assert unfi.filtername is None
     nodemap = unfi.changelog.nodemap
     for s in obsutil.allsuccessors(unfi.obsstore, [unfi[rev].node()]):
         if s in nodemap:
             yield nodemap[s]
 
 def defineparents(repo, rev, destmap, state, skipped, obsskipped):
     """Return new parents and optionally a merge base for rev being rebased
 
     The destination specified by "dest" cannot always be used directly because
     previously rebase result could affect destination. For example,
 
           D E    rebase -r C+D+E -d B
           |/     C will be rebased to C'
         B C      D's new destination will be C' instead of B
         |/       E's new destination will be C' instead of B
         A
 
     The new parents of a merge is slightly more complicated. See the comment
     block below.
     """
     # use unfiltered changelog since successorrevs may return filtered nodes
     assert repo.filtername is None
     cl = repo.changelog
     def isancestor(a, b):
         # take revision numbers instead of nodes
         if a == b:
             return True
         elif a > b:
             return False
         return cl.isancestor(cl.node(a), cl.node(b))
 
     dest = destmap[rev]
     oldps = repo.changelog.parentrevs(rev) # old parents
     newps = [nullrev, nullrev] # new parents
     dests = adjustdest(repo, rev, destmap, state, skipped)
     bases = list(oldps) # merge base candidates, initially just old parents
 
     if all(r == nullrev for r in oldps[1:]):
         # For non-merge changeset, just move p to adjusted dest as requested.
         newps[0] = dests[0]
     else:
         # For merge changeset, if we move p to dests[i] unconditionally, both
         # parents may change and the end result looks like "the merge loses a
         # parent", which is a surprise. This is a limit because "--dest" only
         # accepts one dest per src.
         #
         # Therefore, only move p with reasonable conditions (in this order):
         #   1. use dest, if dest is a descendent of (p or one of p's successors)
         #   2. use p's rebased result, if p is rebased (state[p] > 0)
         #
         # Comparing with adjustdest, the logic here does some additional work:
         #   1. decide which parents will not be moved towards dest
         #   2. if the above decision is "no", should a parent still be moved
         #      because it was rebased?
         #
         # For example:
         #
         #     C    # "rebase -r C -d D" is an error since none of the parents
         #    /|    # can be moved. "rebase -r B+C -d D" will move C's parent
         #   A B D  # B (using rule "2."), since B will be rebased.
         #
         # The loop tries to be not rely on the fact that a Mercurial node has
         # at most 2 parents.
         for i, p in enumerate(oldps):
             np = p # new parent
             if any(isancestor(x, dests[i]) for x in successorrevs(repo, p)):
                 np = dests[i]
             elif p in state and state[p] > 0:
                 np = state[p]
 
             # "bases" only record "special" merge bases that cannot be
             # calculated from changelog DAG (i.e. isancestor(p, np) is False).
             # For example:
             #
             #   B'   # rebase -s B -d D, when B was rebased to B'. dest for C
             #   | C  # is B', but merge base for C is B, instead of
             #   D |  # changelog.ancestor(C, B') == A. If changelog DAG and
             #   | B  # "state" edges are merged (so there will be an edge from
             #   |/   # B to B'), the merge base is still ancestor(C, B') in
             #   A    # the merged graph.
             #
             # Also see https://bz.mercurial-scm.org/show_bug.cgi?id=1950#c8
             # which uses "virtual null merge" to explain this situation.
             if isancestor(p, np):
                 bases[i] = nullrev
 
             # If one parent becomes an ancestor of the other, drop the ancestor
             for j, x in enumerate(newps[:i]):
                 if x == nullrev:
                     continue
                 if isancestor(np, x): # CASE-1
                     np = nullrev
                 elif isancestor(x, np): # CASE-2
                     newps[j] = np
                     np = nullrev
                     # New parents forming an ancestor relationship does not
                     # mean the old parents have a similar relationship. Do not
                     # set bases[x] to nullrev.
                     bases[j], bases[i] = bases[i], bases[j]
 
             newps[i] = np
 
         # "rebasenode" updates to new p1, and the old p1 will be used as merge
         # base. If only p2 changes, merging using unchanged p1 as merge base is
         # suboptimal. Therefore swap parents to make the merge sane.
         if newps[1] != nullrev and oldps[0] == newps[0]:
             assert len(newps) == 2 and len(oldps) == 2
             newps.reverse()
             bases.reverse()
 
         # No parent change might be an error because we fail to make rev a
         # descendent of requested dest. This can happen, for example:
         #
         #     C    # rebase -r C -d D
         #    /|    # None of A and B will be changed to D and rebase fails.
         #   A B D
         if set(newps) == set(oldps) and dest not in newps:
             raise error.Abort(_('cannot rebase %d:%s without '
                                 'moving at least one of its parents')
                               % (rev, repo[rev]))
 
     # Source should not be ancestor of dest. The check here guarantees it's
     # impossible. With multi-dest, the initial check does not cover complex
     # cases since we don't have abstractions to dry-run rebase cheaply.
     if any(p != nullrev and isancestor(rev, p) for p in newps):
         raise error.Abort(_('source is ancestor of destination'))
 
     # "rebasenode" updates to new p1, use the corresponding merge base.
     if bases[0] != nullrev:
         base = bases[0]
     else:
         base = None
 
     # Check if the merge will contain unwanted changes. That may happen if
     # there are multiple special (non-changelog ancestor) merge bases, which
     # cannot be handled well by the 3-way merge algorithm. For example:
     #
     #     F
     #    /|
     #   D E  # "rebase -r D+E+F -d Z", when rebasing F, if "D" was chosen
     #   | |  # as merge base, the difference between D and F will include
     #   B C  # C, so the rebased F will contain C surprisingly. If "E" was
     #   |/   #  chosen, the rebased F will contain B.
     #   A Z
     #
     # But our merge base candidates (D and E in above case) could still be
     # better than the default (ancestor(F, Z) == null). Therefore still
     # pick one (so choose p1 above).
     if sum(1 for b in bases if b != nullrev) > 1:
         unwanted = [None, None] # unwanted[i]: unwanted revs if choose bases[i]
         for i, base in enumerate(bases):
             if base == nullrev:
                 continue
             # Revisions in the side (not chosen as merge base) branch that
             # might contain "surprising" contents
             siderevs = list(repo.revs('((%ld-%d) %% (%d+%d))',
                                       bases, base, base, dest))
 
             # If those revisions are covered by rebaseset, the result is good.
             # A merge in rebaseset would be considered to cover its ancestors.
             if siderevs:
                 rebaseset = [r for r, d in state.items()
                              if d > 0 and r not in obsskipped]
                 merges = [r for r in rebaseset
                           if cl.parentrevs(r)[1] != nullrev]
                 unwanted[i] = list(repo.revs('%ld - (::%ld) - %ld',
                                              siderevs, merges, rebaseset))
 
         # Choose a merge base that has a minimal number of unwanted revs.
         l, i = min((len(revs), i)
                    for i, revs in enumerate(unwanted) if revs is not None)
         base = bases[i]
 
         # newps[0] should match merge base if possible. Currently, if newps[i]
         # is nullrev, the only case is newps[i] and newps[j] (j < i), one is
         # the other's ancestor. In that case, it's fine to not swap newps here.
         # (see CASE-1 and CASE-2 above)
         if i != 0 and newps[i] != nullrev:
             newps[0], newps[i] = newps[i], newps[0]
 
         # The merge will include unwanted revisions. Abort now. Revisit this if
         # we have a more advanced merge algorithm that handles multiple bases.
         if l > 0:
             unwanteddesc = _(' or ').join(
                 (', '.join('%d:%s' % (r, repo[r]) for r in revs)
                  for revs in unwanted if revs is not None))
             raise error.Abort(
                 _('rebasing %d:%s will include unwanted changes from %s')
                 % (rev, repo[rev], unwanteddesc))
 
     repo.ui.debug(" future parents are %d and %d\n" % tuple(newps))
 
     return newps[0], newps[1], base
 
 def isagitpatch(repo, patchname):
     'Return true if the given patch is in git format'
     mqpatch = os.path.join(repo.mq.path, patchname)
     for line in patch.linereader(open(mqpatch, 'rb')):
         if line.startswith('diff --git'):
             return True
     return False
 
 def updatemq(repo, state, skipped, **opts):
     'Update rebased mq patches - finalize and then import them'
     mqrebase = {}
     mq = repo.mq
     original_series = mq.fullseries[:]
     skippedpatches = set()
 
     for p in mq.applied:
         rev = repo[p.node].rev()
         if rev in state:
             repo.ui.debug('revision %d is an mq patch (%s), finalize it.\n' %
                                         (rev, p.name))
             mqrebase[rev] = (p.name, isagitpatch(repo, p.name))
         else:
             # Applied but not rebased, not sure this should happen
             skippedpatches.add(p.name)
 
     if mqrebase:
         mq.finish(repo, mqrebase.keys())
 
         # We must start import from the newest revision
         for rev in sorted(mqrebase, reverse=True):
             if rev not in skipped:
                 name, isgit = mqrebase[rev]
                 repo.ui.note(_('updating mq patch %s to %d:%s\n') %
                              (name, state[rev], repo[state[rev]]))
                 mq.qimport(repo, (), patchname=name, git=isgit,
                                 rev=["%d" % state[rev]])
             else:
                 # Rebased and skipped
                 skippedpatches.add(mqrebase[rev][0])
 
         # Patches were either applied and rebased and imported in
         # order, applied and removed or unapplied. Discard the removed
         # ones while preserving the original series order and guards.
         newseries = [s for s in original_series
                      if mq.guard_re.split(s, 1)[0] not in skippedpatches]
         mq.fullseries[:] = newseries
         mq.seriesdirty = True
         mq.savedirty()
 
 def storecollapsemsg(repo, collapsemsg):
     'Store the collapse message to allow recovery'
     collapsemsg = collapsemsg or ''
     f = repo.vfs("last-message.txt", "w")
     f.write("%s\n" % collapsemsg)
     f.close()
 
 def clearcollapsemsg(repo):
     'Remove collapse message file'
     repo.vfs.unlinkpath("last-message.txt", ignoremissing=True)
 
 def restorecollapsemsg(repo, isabort):
     'Restore previously stored collapse message'
     try:
         f = repo.vfs("last-message.txt")
         collapsemsg = f.readline().strip()
         f.close()
     except IOError as err:
         if err.errno != errno.ENOENT:
             raise
         if isabort:
             # Oh well, just abort like normal
             collapsemsg = ''
         else:
             raise error.Abort(_('missing .hg/last-message.txt for rebase'))
     return collapsemsg
 
 def clearstatus(repo):
     'Remove the status files'
     # Make sure the active transaction won't write the state file
     tr = repo.currenttransaction()
     if tr:
         tr.removefilegenerator('rebasestate')
     repo.vfs.unlinkpath("rebasestate", ignoremissing=True)
 
 def needupdate(repo, state):
     '''check whether we should `update --clean` away from a merge, or if
     somehow the working dir got forcibly updated, e.g. by older hg'''
     parents = [p.rev() for p in repo[None].parents()]
 
     # Are we in a merge state at all?
     if len(parents) < 2:
         return False
 
     # We should be standing on the first as-of-yet unrebased commit.
     firstunrebased = min([old for old, new in state.iteritems()
                           if new == nullrev])
     if firstunrebased in parents:
         return True
 
     return False
 
 def abort(repo, originalwd, destmap, state, activebookmark=None):
     '''Restore the repository to its original state.  Additional args:
 
     activebookmark: the name of the bookmark that should be active after the
         restore'''
 
     try:
         # If the first commits in the rebased set get skipped during the rebase,
         # their values within the state mapping will be the dest rev id. The
         # dstates list must must not contain the dest rev (issue4896)
         dstates = [s for r, s in state.items() if s >= 0 and s != destmap[r]]
         immutable = [d for d in dstates if not repo[d].mutable()]
         cleanup = True
         if immutable:
             repo.ui.warn(_("warning: can't clean up public changesets %s\n")
                         % ', '.join(bytes(repo[r]) for r in immutable),
                         hint=_("see 'hg help phases' for details"))
             cleanup = False
 
         descendants = set()
         if dstates:
             descendants = set(repo.changelog.descendants(dstates))
         if descendants - set(dstates):
             repo.ui.warn(_("warning: new changesets detected on destination "
                            "branch, can't strip\n"))
             cleanup = False
 
         if cleanup:
             shouldupdate = False
             rebased = [s for r, s in state.items()
                        if s >= 0 and s != destmap[r]]
             if rebased:
                 strippoints = [
                         c.node() for c in repo.set('roots(%ld)', rebased)]
 
             updateifonnodes = set(rebased)
             updateifonnodes.update(destmap.values())
             updateifonnodes.add(originalwd)
             shouldupdate = repo['.'].rev() in updateifonnodes
 
             # Update away from the rebase if necessary
             if shouldupdate or needupdate(repo, state):
                 mergemod.update(repo, originalwd, False, True)
 
             # Strip from the first rebased revision
             if rebased:
                 # no backup of rebased cset versions needed
                 repair.strip(repo.ui, repo, strippoints)
 
         if activebookmark and activebookmark in repo._bookmarks:
             bookmarks.activate(repo, activebookmark)
 
     finally:
         clearstatus(repo)
         clearcollapsemsg(repo)
         repo.ui.warn(_('rebase aborted\n'))
     return 0
 
 def sortsource(destmap):
     """yield source revisions in an order that we only rebase things once
 
     If source and destination overlaps, we should filter out revisions
     depending on other revisions which hasn't been rebased yet.
 
     Yield a sorted list of revisions each time.
 
     For example, when rebasing A to B, B to C. This function yields [B], then
     [A], indicating B needs to be rebased first.
 
     Raise if there is a cycle so the rebase is impossible.
     """
     srcset = set(destmap)
     while srcset:
         srclist = sorted(srcset)
         result = []
         for r in srclist:
             if destmap[r] not in srcset:
                 result.append(r)
         if not result:
             raise error.Abort(_('source and destination form a cycle'))
         srcset -= set(result)
         yield result
 
 def buildstate(repo, destmap, collapse):
     '''Define which revisions are going to be rebased and where
 
     repo: repo
     destmap: {srcrev: destrev}
     '''
     rebaseset = destmap.keys()
     originalwd = repo['.'].rev()
 
     # This check isn't strictly necessary, since mq detects commits over an
     # applied patch. But it prevents messing up the working directory when
     # a partially completed rebase is blocked by mq.
     if 'qtip' in repo.tags():
         mqapplied = set(repo[s.node].rev() for s in repo.mq.applied)
         if set(destmap.values()) & mqapplied:
             raise error.Abort(_('cannot rebase onto an applied mq patch'))
 
     # Get "cycle" error early by exhausting the generator.
     sortedsrc = list(sortsource(destmap)) # a list of sorted revs
     if not sortedsrc:
         raise error.Abort(_('no matching revisions'))
 
     # Only check the first batch of revisions to rebase not depending on other
     # rebaseset. This means "source is ancestor of destination" for the second
     # (and following) batches of revisions are not checked here. We rely on
     # "defineparents" to do that check.
     roots = list(repo.set('roots(%ld)', sortedsrc[0]))
     if not roots:
         raise error.Abort(_('no matching revisions'))
     def revof(r):
         return r.rev()
     roots = sorted(roots, key=revof)
     state = dict.fromkeys(rebaseset, revtodo)
     emptyrebase = (len(sortedsrc) == 1)
     for root in roots:
         dest = repo[destmap[root.rev()]]
         commonbase = root.ancestor(dest)
         if commonbase == root:
             raise error.Abort(_('source is ancestor of destination'))
         if commonbase == dest:
             wctx = repo[None]
             if dest == wctx.p1():
                 # when rebasing to '.', it will use the current wd branch name
                 samebranch = root.branch() == wctx.branch()
             else:
                 samebranch = root.branch() == dest.branch()
             if not collapse and samebranch and dest in root.parents():
                 # mark the revision as done by setting its new revision
                 # equal to its old (current) revisions
                 state[root.rev()] = root.rev()
                 repo.ui.debug('source is a child of destination\n')
                 continue
 
         emptyrebase = False
         repo.ui.debug('rebase onto %s starting from %s\n' % (dest, root))
     if emptyrebase:
         return None
     for rev in sorted(state):
         parents = [p for p in repo.changelog.parentrevs(rev) if p != nullrev]
         # if all parents of this revision are done, then so is this revision
         if parents and all((state.get(p) == p for p in parents)):
             state[rev] = rev
     return originalwd, destmap, state
 
 def clearrebased(ui, repo, destmap, state, skipped, collapsedas=None,
                  keepf=False, fm=None):
     """dispose of rebased revision at the end of the rebase
 
     If `collapsedas` is not None, the rebase was a collapse whose result if the
     `collapsedas` node.
 
     If `keepf` is not True, the rebase has --keep set and no nodes should be
     removed (but bookmarks still need to be moved).
     """
     tonode = repo.changelog.node
     replacements = {}
     moves = {}
     for rev, newrev in sorted(state.items()):
         if newrev >= 0 and newrev != rev:
             oldnode = tonode(rev)
             newnode = collapsedas or tonode(newrev)
             moves[oldnode] = newnode
             if not keepf:
                 if rev in skipped:
                     succs = ()
                 else:
                     succs = (newnode,)
                 replacements[oldnode] = succs
     scmutil.cleanupnodes(repo, replacements, 'rebase', moves)
     if fm:
         hf = fm.hexfunc
         fl = fm.formatlist
         fd = fm.formatdict
         nodechanges = fd({hf(oldn): fl([hf(n) for n in newn], name='node')
                           for oldn, newn in replacements.iteritems()},
                          key="oldnode", value="newnodes")
         fm.data(nodechanges=nodechanges)
 
 def pullrebase(orig, ui, repo, *args, **opts):
     'Call rebase after pull if the latter has been invoked with --rebase'
     ret = None
     if opts.get(r'rebase'):
         if ui.configbool('commands', 'rebase.requiredest'):
             msg = _('rebase destination required by configuration')
             hint = _('use hg pull followed by hg rebase -d DEST')
             raise error.Abort(msg, hint=hint)
 
         with repo.wlock(), repo.lock():
             if opts.get(r'update'):
                 del opts[r'update']
                 ui.debug('--update and --rebase are not compatible, ignoring '
                          'the update flag\n')
 
             cmdutil.checkunfinished(repo)
             cmdutil.bailifchanged(repo, hint=_('cannot pull with rebase: '
                 'please commit or shelve your changes first'))
 
             revsprepull = len(repo)
             origpostincoming = commands.postincoming
             def _dummy(*args, **kwargs):
                 pass
             commands.postincoming = _dummy
             try:
                 ret = orig(ui, repo, *args, **opts)
             finally:
                 commands.postincoming = origpostincoming
             revspostpull = len(repo)
             if revspostpull > revsprepull:
                 # --rev option from pull conflict with rebase own --rev
                 # dropping it
                 if r'rev' in opts:
                     del opts[r'rev']
                 # positional argument from pull conflicts with rebase's own
                 # --source.
                 if r'source' in opts:
                     del opts[r'source']
                 # revsprepull is the len of the repo, not revnum of tip.
                 destspace = list(repo.changelog.revs(start=revsprepull))
                 opts[r'_destspace'] = destspace
                 try:
                     rebase(ui, repo, **opts)
                 except error.NoMergeDestAbort:
                     # we can maybe update instead
                     rev, _a, _b = destutil.destupdate(repo)
                     if rev == repo['.'].rev():
                         ui.status(_('nothing to rebase\n'))
                     else:
                         ui.status(_('nothing to rebase - updating instead\n'))
                         # not passing argument to get the bare update behavior
                         # with warning and trumpets
                         commands.update(ui, repo)
     else:
         if opts.get(r'tool'):
             raise error.Abort(_('--tool can only be used with --rebase'))
         ret = orig(ui, repo, *args, **opts)
 
     return ret
 
 def _filterobsoleterevs(repo, revs):
     """returns a set of the obsolete revisions in revs"""
     return set(r for r in revs if repo[r].obsolete())
 
 def _computeobsoletenotrebased(repo, rebaseobsrevs, destmap):
     """Return (obsoletenotrebased, obsoletewithoutsuccessorindestination).
 
     `obsoletenotrebased` is a mapping mapping obsolete => successor for all
     obsolete nodes to be rebased given in `rebaseobsrevs`.
 
     `obsoletewithoutsuccessorindestination` is a set with obsolete revisions
     without a successor in destination.
 
     `obsoleteextinctsuccessors` is a set of obsolete revisions with only
     obsolete successors.
     """
     obsoletenotrebased = {}
     obsoletewithoutsuccessorindestination = set([])
     obsoleteextinctsuccessors = set([])
 
     assert repo.filtername is None
     cl = repo.changelog
     nodemap = cl.nodemap
     extinctnodes = set(cl.node(r) for r in repo.revs('extinct()'))
     for srcrev in rebaseobsrevs:
         srcnode = cl.node(srcrev)
         destnode = cl.node(destmap[srcrev])
         # XXX: more advanced APIs are required to handle split correctly
         successors = set(obsutil.allsuccessors(repo.obsstore, [srcnode]))
         # obsutil.allsuccessors includes node itself
         successors.remove(srcnode)
         if successors.issubset(extinctnodes):
             # all successors are extinct
             obsoleteextinctsuccessors.add(srcrev)
         if not successors:
             # no successor
             obsoletenotrebased[srcrev] = None
         else:
             for succnode in successors:
                 if succnode not in nodemap:
                     continue
                 if cl.isancestor(succnode, destnode):
                     obsoletenotrebased[srcrev] = nodemap[succnode]
                     break
             else:
                 # If 'srcrev' has a successor in rebase set but none in
                 # destination (which would be catched above), we shall skip it
                 # and its descendants to avoid divergence.
                 if any(nodemap[s] in destmap for s in successors):
                     obsoletewithoutsuccessorindestination.add(srcrev)
 
     return (
         obsoletenotrebased,
         obsoletewithoutsuccessorindestination,
         obsoleteextinctsuccessors,
     )
 
 def summaryhook(ui, repo):
     if not repo.vfs.exists('rebasestate'):
         return
     try:
         rbsrt = rebaseruntime(repo, ui, {})
         rbsrt.restorestatus()
         state = rbsrt.state
     except error.RepoLookupError:
         # i18n: column positioning for "hg summary"
         msg = _('rebase: (use "hg rebase --abort" to clear broken state)\n')
         ui.write(msg)
         return
     numrebased = len([i for i in state.itervalues() if i >= 0])
     # i18n: column positioning for "hg summary"
     ui.write(_('rebase: %s, %s (rebase --continue)\n') %
              (ui.label(_('%d rebased'), 'rebase.rebased') % numrebased,
               ui.label(_('%d remaining'), 'rebase.remaining') %
               (len(state) - numrebased)))
 
 def uisetup(ui):
     #Replace pull with a decorator to provide --rebase option
     entry = extensions.wrapcommand(commands.table, 'pull', pullrebase)
     entry[1].append(('', 'rebase', None,
                      _("rebase working directory to branch head")))
     entry[1].append(('t', 'tool', '',
                      _("specify merge tool for rebase")))
     cmdutil.summaryhooks.add('rebase', summaryhook)
     cmdutil.unfinishedstates.append(
         ['rebasestate', False, False, _('rebase in progress'),
          _("use 'hg rebase --continue' or 'hg rebase --abort'")])
     cmdutil.afterresolvedstates.append(
         ['rebasestate', _('hg rebase --continue')])