hgext/rebase.py

# 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 mercurial import hg, util, repair, merge, cmdutil, commands, bookmarks
from mercurial import extensions, patch, scmutil, phases, obsolete, error
from mercurial import copies, repoview, revset
from mercurial.commands import templateopts
from mercurial.node import nullrev, nullid, hex, short
from mercurial.lock import release
from mercurial.i18n import _
import os, errno

# 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
nullmerge = -2
revignored = -3
# successor in rebase destination
revprecursor = -4
# plain prune (no successor)
revpruned = -5
revskipped = (revignored, revprecursor, revpruned)

cmdtable = {}
command = cmdutil.command(cmdtable)
# Note for extension authors: ONLY specify testedwith = 'internal' 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 = 'internal'

def _nothingtorebase():
    return 1

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):
    # Destination defaults to the latest revision in the
    # current branch
    branch = repo[None].branch()
    return repo[branch].rev()

revsetpredicate = revset.extpredicate()

@revsetpredicate('_destrebase')
def _revsetdestrebase(repo, subset, x):
    # ``_rebasedefaultdest()``

    # default destination for rebase.
    # # XXX: Currently private because I expect the signature to change.
    # # XXX: - taking rev as arguments,
    # # XXX: - bailing out in case of ambiguity vs returning all data.
    # # XXX: - probably merging with the merge destination.
    # i18n: "_rebasedefaultdest" is a keyword
    revset.getargs(x, 0, 0, _("_rebasedefaultdest takes no arguments"))
    return subset & revset.baseset([_destrebase(repo)])

@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'))] +
     templateopts,
    _('[-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 uses the current branch tip as the destination. (The
    destination changeset is not modified by rebasing, but new
    changesets are added as its descendants.)

    There are three 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.

    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 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

    Returns 0 on success, 1 if nothing to rebase or there are
    unresolved conflicts.

    """
    originalwd = target = None
    activebookmark = None
    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.
    state = {}
    skipped = set()
    targetancestors = set()


    lock = wlock = None
    try:
        wlock = repo.wlock()
        lock = 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', [])
        contf = opts.get('continue')
        abortf = opts.get('abort')
        collapsef = opts.get('collapse', False)
        collapsemsg = cmdutil.logmessage(ui, opts)
        date = opts.get('date', None)
        e = opts.get('extrafn') # internal, used by e.g. hgsubversion
        extrafns = []
        if e:
            extrafns = [e]
        keepf = opts.get('keep', False)
        keepbranchesf = opts.get('keepbranches', False)
        # keepopen is not meant for use on the command line, but by
        # other extensions
        keepopen = opts.get('keepopen', False)

        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 collapsemsg and not 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 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'))

            try:
                (originalwd, target, state, skipped, collapsef, keepf,
                 keepbranchesf, external, activebookmark) = restorestatus(repo)
            except error.RepoLookupError:
                if abortf:
                    clearstatus(repo)
                    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 abortf:
                return abort(repo, originalwd, target, state,
                             activebookmark=activebookmark)
        else:
            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'))

            cmdutil.checkunfinished(repo)
            cmdutil.bailifchanged(repo)

            if destf:
                dest = scmutil.revsingle(repo, destf)
            else:
                dest = repo[_destrebase(repo)]
                destf = str(dest)

            if revf:
                rebaseset = scmutil.revrange(repo, revf)
                if not rebaseset:
                    ui.status(_('empty "rev" revision set - '
                                'nothing to rebase\n'))
                    return _nothingtorebase()
            elif srcf:
                src = scmutil.revrange(repo, [srcf])
                if not src:
                    ui.status(_('empty "source" revision set - '
                                'nothing to rebase\n'))
                    return _nothingtorebase()
                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 _nothingtorebase()
                commonanc = repo.revs('ancestor(%ld, %d)', base, dest).first()
                if commonanc is not None:
                    rebaseset = repo.revs('(%d::(%ld) - %d)::',
                                          commonanc, base, commonanc)
                else:
                    rebaseset = []

                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):
                        if basef:
                            ui.status(_('nothing to rebase - "base" %s is '
                                        'already an ancestor of destination '
                                        '%s\n') %
                                      ('+'.join(str(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(str(repo[r]) for r in base), dest))
                    return _nothingtorebase()

            allowunstable = obsolete.isenabled(repo, obsolete.allowunstableopt)
            if (not (keepf or allowunstable)
                  and 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'))

            obsoletenotrebased = {}
            if ui.configbool('experimental', 'rebaseskipobsolete'):
                rebasesetrevs = set(rebaseset)
                obsoletenotrebased = _computeobsoletenotrebased(repo,
                                                                rebasesetrevs,
                                                                dest)

                # - plain prune (no successor) changesets are rebased
                # - split changesets are not rebased if at least one of the
                # changeset resulting from the split is an ancestor of dest
                rebaseset = rebasesetrevs - set(obsoletenotrebased)
                if rebasesetrevs and not rebaseset:
                    msg = _('all requested changesets have equivalents '
                            'or were marked as obsolete')
                    hint = _('to force the rebase, set the config '
                             'experimental.rebaseskipobsolete to False')
                    raise error.Abort(msg, hint=hint)

            result = buildstate(repo, dest, rebaseset, collapsef,
                                obsoletenotrebased)

            if not result:
                # Empty state built, nothing to rebase
                ui.status(_('nothing to rebase\n'))
                return _nothingtorebase()

            root = min(rebaseset)
            if not keepf and not repo[root].mutable():
                raise error.Abort(_("can't rebase public changeset %s")
                                 % repo[root],
                                 hint=_('see "hg help phases" for details'))

            originalwd, target, state = result
            if collapsef:
                targetancestors = repo.changelog.ancestors([target],
                                                           inclusive=True)
                external = externalparent(repo, state, targetancestors)

            if dest.closesbranch() and not keepbranchesf:
                ui.status(_('reopening closed branch head %s\n') % dest)

        if keepbranchesf and collapsef:
            branches = set()
            for rev in state:
                branches.add(repo[rev].branch())
                if len(branches) > 1:
                    raise error.Abort(_('cannot collapse multiple named '
                                        'branches'))

        # Rebase
        if not targetancestors:
            targetancestors = repo.changelog.ancestors([target], inclusive=True)

        # Keep track of the current bookmarks in order to reset them later
        currentbookmarks = repo._bookmarks.copy()
        activebookmark = activebookmark or repo._activebookmark
        if activebookmark:
            bookmarks.deactivate(repo)

        extrafn = _makeextrafn(extrafns)

        sortedstate = sorted(state)
        total = len(sortedstate)
        pos = 0
        for rev in sortedstate:
            ctx = repo[rev]
            desc = '%d:%s "%s"' % (ctx.rev(), ctx,
                                   ctx.description().split('\n', 1)[0])
            names = repo.nodetags(ctx.node()) + repo.nodebookmarks(ctx.node())
            if names:
                desc += ' (%s)' % ' '.join(names)
            pos += 1
            if state[rev] == revtodo:
                ui.status(_('rebasing %s\n') % desc)
                ui.progress(_("rebasing"), pos, ("%d:%s" % (rev, ctx)),
                            _('changesets'), total)
                p1, p2, base = defineparents(repo, rev, target, state,
                                             targetancestors)
                storestatus(repo, originalwd, target, state, collapsef, keepf,
                            keepbranchesf, external, activebookmark)
                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, state,
                                           collapsef, target)
                        if stats and stats[3] > 0:
                            raise error.InterventionRequired(
                                _('unresolved conflicts (see hg '
                                  'resolve, then hg rebase --continue)'))
                    finally:
                        ui.setconfig('ui', 'forcemerge', '', 'rebase')
                if not collapsef:
                    merging = p2 != nullrev
                    editform = cmdutil.mergeeditform(merging, 'rebase')
                    editor = cmdutil.getcommiteditor(editform=editform, **opts)
                    newnode = concludenode(repo, rev, p1, p2, extrafn=extrafn,
                                           editor=editor,
                                           keepbranches=keepbranchesf,
                                           date=date)
                else:
                    # Skip commit if we are collapsing
                    repo.dirstate.beginparentchange()
                    repo.setparents(repo[p1].node())
                    repo.dirstate.endparentchange()
                    newnode = None
                # Update the state
                if newnode is not None:
                    state[rev] = repo[newnode].rev()
                    ui.debug('rebased as %s\n' % short(newnode))
                else:
                    if not collapsef:
                        ui.warn(_('note: rebase of %d:%s created no changes '
                                  'to commit\n') % (rev, ctx))
                        skipped.add(rev)
                    state[rev] = p1
                    ui.debug('next revision set to %s\n' % p1)
            elif state[rev] == nullmerge:
                ui.debug('ignoring null merge rebase of %s\n' % rev)
            elif state[rev] == revignored:
                ui.status(_('not rebasing ignored %s\n') % desc)
            elif state[rev] == revprecursor:
                targetctx = repo[obsoletenotrebased[rev]]
                desctarget = '%d:%s "%s"' % (targetctx.rev(), targetctx,
                             targetctx.description().split('\n', 1)[0])
                msg = _('note: not rebasing %s, already in destination as %s\n')
                ui.status(msg % (desc, desctarget))
            elif state[rev] == revpruned:
                msg = _('note: not rebasing %s, it has no successor\n')
                ui.status(msg % desc)
            else:
                ui.status(_('already rebased %s as %s\n') %
                          (desc, repo[state[rev]]))

        ui.progress(_('rebasing'), None)
        ui.note(_('rebase merging completed\n'))

        if collapsef and not keepopen:
            p1, p2, _base = defineparents(repo, min(state), target,
                                          state, targetancestors)
            editopt = opts.get('edit')
            editform = 'rebase.collapse'
            if collapsemsg:
                commitmsg = collapsemsg
            else:
                commitmsg = 'Collapsed revision'
                for rebased in state:
                    if rebased not in skipped and state[rebased] > nullmerge:
                        commitmsg += '\n* %s' % repo[rebased].description()
                editopt = True
            editor = cmdutil.getcommiteditor(edit=editopt, editform=editform)
            newnode = concludenode(repo, rev, p1, external, commitmsg=commitmsg,
                                   extrafn=extrafn, editor=editor,
                                   keepbranches=keepbranchesf,
                                   date=date)
            if newnode is None:
                newrev = target
            else:
                newrev = repo[newnode].rev()
            for oldrev in state.iterkeys():
                if state[oldrev] > nullmerge:
                    state[oldrev] = newrev

        if 'qtip' in repo.tags():
            updatemq(repo, state, skipped, **opts)

        if currentbookmarks:
            # Nodeids are needed to reset bookmarks
            nstate = {}
            for k, v in state.iteritems():
                if v > nullmerge:
                    nstate[repo[k].node()] = repo[v].node()
            # XXX this is the same as dest.node() for the non-continue path --
            # this should probably be cleaned up
            targetnode = repo[target].node()

        # restore original working directory
        # (we do this before stripping)
        newwd = state.get(originalwd, originalwd)
        if newwd < 0:
            # original directory is a parent of rebase set root or ignored
            newwd = originalwd
        if newwd not in [c.rev() for c in repo[None].parents()]:
            ui.note(_("update back to initial working directory parent\n"))
            hg.updaterepo(repo, newwd, False)

        if not keepf:
            collapsedas = None
            if collapsef:
                collapsedas = newnode
            clearrebased(ui, repo, state, skipped, collapsedas)

        tr = None
        try:
            tr = repo.transaction('bookmark')
            if currentbookmarks:
                updatebookmarks(repo, targetnode, nstate, currentbookmarks, tr)
                if activebookmark not in repo._bookmarks:
                    # active bookmark was divergent one and has been deleted
                    activebookmark = None
            tr.close()
        finally:
            release(tr)
        clearstatus(repo)

        ui.note(_("rebase completed\n"))
        util.unlinkpath(repo.sjoin('undo'), ignoremissing=True)
        if skipped:
            ui.note(_("%d revisions have been skipped\n") % len(skipped))

        if (activebookmark and
            repo['.'].node() == repo._bookmarks[activebookmark]):
                bookmarks.activate(repo, activebookmark)

    finally:
        release(lock, wlock)

def externalparent(repo, state, targetancestors):
    """Return the revision that should be used as the second parent
    when the revisions in state is collapsed on top of targetancestors.
    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 targetancestors):
                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 %s, there is more '
                       'than one external parent: %s') %
                     (max(targetancestors),
                      ', '.join(str(p) for p in sorted(parents))))

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 = cmdutil.dirstateguard(repo, 'rebase')
    try:
        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 = ctx.extra().copy()
        if not keepbranches:
            del extra['branch']
        extra['rebase_source'] = ctx.hex()
        if extrafn:
            extrafn(ctx, extra)

        backup = repo.ui.backupconfig('phases', 'new-commit')
        try:
            targetphase = max(ctx.phase(), phases.draft)
            repo.ui.setconfig('phases', 'new-commit', targetphase, '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)
        finally:
            repo.ui.restoreconfig(backup)

        repo.dirstate.setbranch(repo[newnode].branch())
        dsguard.close()
        return newnode
    finally:
        release(dsguard)

def rebasenode(repo, rev, p1, base, state, collapse, target):
    'Rebase a single revision rev on top of p1 using base as merge ancestor'
    # Merge phase
    # Update to target and merge it with local
    if repo['.'].rev() != p1:
        repo.ui.debug(" update to %d:%s\n" % (p1, repo[p1]))
        merge.update(repo, p1, False, True)
    else:
        repo.ui.debug(" already in target\n")
    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 = merge.update(repo, rev, True, True, base, collapse,
                        labels=['dest', 'source'])
    if collapse:
        copies.duplicatecopies(repo, rev, target)
    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, rev, p1rev, skiprev=target)
    return stats

def nearestrebased(repo, rev, state):
    """return the nearest ancestors of rev in the rebase result"""
    rebased = [r for r in state if state[r] > nullmerge]
    candidates = repo.revs('max(%ld  and (::%d))', rebased, rev)
    if candidates:
        return state[candidates.first()]
    else:
        return None

def defineparents(repo, rev, target, state, targetancestors):
    'Return the new parent relationship of the revision that will be rebased'
    parents = repo[rev].parents()
    p1 = p2 = nullrev

    p1n = parents[0].rev()
    if p1n in targetancestors:
        p1 = target
    elif p1n in state:
        if state[p1n] == nullmerge:
            p1 = target
        elif state[p1n] in revskipped:
            p1 = nearestrebased(repo, p1n, state)
            if p1 is None:
                p1 = target
        else:
            p1 = state[p1n]
    else: # p1n external
        p1 = target
        p2 = p1n

    if len(parents) == 2 and parents[1].rev() not in targetancestors:
        p2n = parents[1].rev()
        # interesting second parent
        if p2n in state:
            if p1 == target: # p1n in targetancestors or external
                p1 = state[p2n]
            elif state[p2n] in revskipped:
                p2 = nearestrebased(repo, p2n, state)
                if p2 is None:
                    # no ancestors rebased yet, detach
                    p2 = target
            else:
                p2 = state[p2n]
        else: # p2n external
            if p2 != nullrev: # p1n external too => rev is a merged revision
                raise error.Abort(_('cannot use revision %d as base, result '
                        'would have 3 parents') % rev)
            p2 = p2n
    repo.ui.debug(" future parents are %d and %d\n" %
                            (repo[p1].rev(), repo[p2].rev()))

    if rev == min(state):
        # Case (1) initial changeset of a non-detaching rebase.
        # Let the merge mechanism find the base itself.
        base = None
    elif not repo[rev].p2():
        # Case (2) detaching the node with a single parent, use this parent
        base = repo[rev].p1().rev()
    else:
        # Assuming there is a p1, this is the case where there also is a p2.
        # We are thus rebasing a merge and need to pick the right merge base.
        #
        # Imagine we have:
        # - M: current rebase revision in this step
        # - A: one parent of M
        # - B: other parent of M
        # - D: destination of this merge step (p1 var)
        #
        # Consider the case where D is a descendant of A or B and the other is
        # 'outside'. In this case, the right merge base is the D ancestor.
        #
        # An informal proof, assuming A is 'outside' and B is the D ancestor:
        #
        # If we pick B as the base, the merge involves:
        # - changes from B to M (actual changeset payload)
        # - changes from B to D (induced by rebase) as D is a rebased
        #   version of B)
        # Which exactly represent the rebase operation.
        #
        # If we pick A as the base, the merge involves:
        # - changes from A to M (actual changeset payload)
        # - changes from A to D (with include changes between unrelated A and B
        #   plus changes induced by rebase)
        # Which does not represent anything sensible and creates a lot of
        # conflicts. A is thus not the right choice - B is.
        #
        # Note: The base found in this 'proof' is only correct in the specified
        # case. This base does not make sense if is not D a descendant of A or B
        # or if the other is not parent 'outside' (especially not if the other
        # parent has been rebased). The current implementation does not
        # make it feasible to consider different cases separately. In these
        # other cases we currently just leave it to the user to correctly
        # resolve an impossible merge using a wrong ancestor.
        for p in repo[rev].parents():
            if state.get(p.rev()) == p1:
                base = p.rev()
                break
        else: # fallback when base not found
            base = None

            # Raise because this function is called wrong (see issue 4106)
            raise AssertionError('no base found to rebase on '
                                 '(defineparents called wrong)')
    return p1, p2, 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(file(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 %s:%s\n') %
                             (name, state[rev], repo[state[rev]]))
                mq.qimport(repo, (), patchname=name, git=isgit,
                                rev=[str(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 updatebookmarks(repo, targetnode, nstate, originalbookmarks, tr):
    'Move bookmarks to their correct changesets, and delete divergent ones'
    marks = repo._bookmarks
    for k, v in originalbookmarks.iteritems():
        if v in nstate:
            # update the bookmarks for revs that have moved
            marks[k] = nstate[v]
            bookmarks.deletedivergent(repo, [targetnode], k)
    marks.recordchange(tr)

def storestatus(repo, originalwd, target, state, collapse, keep, keepbranches,
                external, activebookmark):
    'Store the current status to allow recovery'
    f = repo.vfs("rebasestate", "w")
    f.write(repo[originalwd].hex() + '\n')
    f.write(repo[target].hex() + '\n')
    f.write(repo[external].hex() + '\n')
    f.write('%d\n' % int(collapse))
    f.write('%d\n' % int(keep))
    f.write('%d\n' % int(keepbranches))
    f.write('%s\n' % (activebookmark or ''))
    for d, v in state.iteritems():
        oldrev = repo[d].hex()
        if v >= 0:
            newrev = repo[v].hex()
        elif v == revtodo:
            # To maintain format compatibility, we have to use nullid.
            # Please do remove this special case when upgrading the format.
            newrev = hex(nullid)
        else:
            newrev = v
        f.write("%s:%s\n" % (oldrev, newrev))
    f.close()
    repo.ui.debug('rebase status stored\n')

def clearstatus(repo):
    'Remove the status files'
    _clearrebasesetvisibiliy(repo)
    util.unlinkpath(repo.join("rebasestate"), ignoremissing=True)

def restorestatus(repo):
    'Restore a previously stored status'
    keepbranches = None
    target = None
    collapse = False
    external = nullrev
    activebookmark = None
    state = {}

    try:
        f = repo.vfs("rebasestate")
        for i, l in enumerate(f.read().splitlines()):
            if i == 0:
                originalwd = repo[l].rev()
            elif i == 1:
                target = 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:
                oldrev, newrev = l.split(':')
                if newrev in (str(nullmerge), str(revignored),
                              str(revprecursor), str(revpruned)):
                    state[repo[oldrev].rev()] = int(newrev)
                elif newrev == nullid:
                    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
        raise error.Abort(_('no rebase in progress'))

    if keepbranches is None:
        raise error.Abort(_('.hg/rebasestate is incomplete'))

    skipped = set()
    # recompute the set of skipped revs
    if not collapse:
        seen = set([target])
        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(str(r) for r in sorted(skipped)) or None))
    repo.ui.debug('rebase status resumed\n')
    _setrebasesetvisibility(repo, state.keys())
    return (originalwd, target, state, skipped,
            collapse, keep, keepbranches, external, activebookmark)

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, target, 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 target rev id. The
        # dstates list must must not contain the target rev (issue4896)
        dstates = [s for s in state.values() if s >= 0 and s != target]
        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(str(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 target branch, "
                        "can't strip\n"))
            cleanup = False

        if cleanup:
            # Update away from the rebase if necessary
            if needupdate(repo, state):
                merge.update(repo, originalwd, False, True)

            # Strip from the first rebased revision
            rebased = filter(lambda x: x >= 0 and x != target, state.values())
            if rebased:
                strippoints = [
                        c.node()  for c in repo.set('roots(%ld)', 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)
        repo.ui.warn(_('rebase aborted\n'))
    return 0

def buildstate(repo, dest, rebaseset, collapse, obsoletenotrebased):
    '''Define which revisions are going to be rebased and where

    repo: repo
    dest: context
    rebaseset: set of rev
    '''
    _setrebasesetvisibility(repo, rebaseset)

    # 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() and (dest.node() in
                            [s.node for s in repo.mq.applied]):
        raise error.Abort(_('cannot rebase onto an applied mq patch'))

    roots = list(repo.set('roots(%ld)', rebaseset))
    if not roots:
        raise error.Abort(_('no matching revisions'))
    roots.sort()
    state = {}
    detachset = set()
    for root in roots:
        commonbase = root.ancestor(dest)
        if commonbase == root:
            raise error.Abort(_('source is ancestor of destination'))
        if commonbase == dest:
            samebranch = root.branch() == dest.branch()
            if not collapse and samebranch and root in dest.children():
                repo.ui.debug('source is a child of destination\n')
                return None

        repo.ui.debug('rebase onto %d starting from %s\n' % (dest, root))
        state.update(dict.fromkeys(rebaseset, revtodo))
        # Rebase tries to turn <dest> into a parent of <root> while
        # preserving the number of parents of rebased changesets:
        #
        # - A changeset with a single parent will always be rebased as a
        #   changeset with a single parent.
        #
        # - A merge will be rebased as merge unless its parents are both
        #   ancestors of <dest> or are themselves in the rebased set and
        #   pruned while rebased.
        #
        # If one parent of <root> is an ancestor of <dest>, the rebased
        # version of this parent will be <dest>. This is always true with
        # --base option.
        #
        # Otherwise, we need to *replace* the original parents with
        # <dest>. This "detaches" the rebased set from its former location
        # and rebases it onto <dest>. Changes introduced by ancestors of
        # <root> not common with <dest> (the detachset, marked as
        # nullmerge) are "removed" from the rebased changesets.
        #
        # - If <root> has a single parent, set it to <dest>.
        #
        # - If <root> is a merge, we cannot decide which parent to
        #   replace, the rebase operation is not clearly defined.
        #
        # The table below sums up this behavior:
        #
        # +------------------+----------------------+-------------------------+
        # |                  |     one parent       |  merge                  |
        # +------------------+----------------------+-------------------------+
        # | parent in        | new parent is <dest> | parents in ::<dest> are |
        # | ::<dest>         |                      | remapped to <dest>      |
        # +------------------+----------------------+-------------------------+
        # | unrelated source | new parent is <dest> | ambiguous, abort        |
        # +------------------+----------------------+-------------------------+
        #
        # The actual abort is handled by `defineparents`
        if len(root.parents()) <= 1:
            # ancestors of <root> not ancestors of <dest>
            detachset.update(repo.changelog.findmissingrevs([commonbase.rev()],
                                                            [root.rev()]))
    for r in detachset:
        if r not in state:
            state[r] = nullmerge
    if len(roots) > 1:
        # If we have multiple roots, we may have "hole" in the rebase set.
        # Rebase roots that descend from those "hole" should not be detached as
        # other root are. We use the special `revignored` to inform rebase that
        # the revision should be ignored but that `defineparents` should search
        # a rebase destination that make sense regarding rebased topology.
        rebasedomain = set(repo.revs('%ld::%ld', rebaseset, rebaseset))
        for ignored in set(rebasedomain) - set(rebaseset):
            state[ignored] = revignored
    for r in obsoletenotrebased:
        if obsoletenotrebased[r] is None:
            state[r] = revpruned
        else:
            state[r] = revprecursor
    return repo['.'].rev(), dest.rev(), state

def clearrebased(ui, repo, state, skipped, collapsedas=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 obsolete.isenabled(repo, obsolete.createmarkersopt):
        markers = []
        for rev, newrev in sorted(state.items()):
            if newrev >= 0:
                if rev in skipped:
                    succs = ()
                elif collapsedas is not None:
                    succs = (repo[collapsedas],)
                else:
                    succs = (repo[newrev],)
                markers.append((repo[rev], succs))
        if markers:
            obsolete.createmarkers(repo, markers)
    else:
        rebased = [rev for rev in state if state[rev] > nullmerge]
        if rebased:
            stripped = []
            for root in repo.set('roots(%ld)', rebased):
                if set(repo.changelog.descendants([root.rev()])) - set(state):
                    ui.warn(_("warning: new changesets detected "
                              "on source branch, not stripping\n"))
                else:
                    stripped.append(root.node())
            if stripped:
                # backup the old csets by default
                repair.strip(ui, repo, stripped, "all")


def pullrebase(orig, ui, repo, *args, **opts):
    'Call rebase after pull if the latter has been invoked with --rebase'
    ret = None
    if opts.get('rebase'):
        wlock = lock = None
        try:
            wlock = repo.wlock()
            lock = repo.lock()
            if opts.get('update'):
                del opts['update']
                ui.debug('--update and --rebase are not compatible, ignoring '
                         'the update flag\n')

            movemarkfrom = repo['.'].node()
            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 'rev' in opts:
                    del opts['rev']
                # positional argument from pull conflicts with rebase's own
                # --source.
                if 'source' in opts:
                    del opts['source']
                rebase(ui, repo, **opts)
                branch = repo[None].branch()
                dest = repo[branch].rev()
                if dest != repo['.'].rev():
                    # there was nothing to rebase we force an update
                    hg.update(repo, dest)
                    if bookmarks.update(repo, [movemarkfrom], repo['.'].node()):
                        ui.status(_("updating bookmark %s\n")
                                  % repo._activebookmark)
        finally:
            release(lock, wlock)
    else:
        if opts.get('tool'):
            raise error.Abort(_('--tool can only be used with --rebase'))
        ret = orig(ui, repo, *args, **opts)

    return ret

def _setrebasesetvisibility(repo, revs):
    """store the currently rebased set on the repo object

    This is used by another function to prevent rebased revision to because
    hidden (see issue4505)"""
    repo = repo.unfiltered()
    revs = set(revs)
    repo._rebaseset = revs
    # invalidate cache if visibility changes
    hiddens = repo.filteredrevcache.get('visible', set())
    if revs & hiddens:
        repo.invalidatevolatilesets()

def _clearrebasesetvisibiliy(repo):
    """remove rebaseset data from the repo"""
    repo = repo.unfiltered()
    if '_rebaseset' in vars(repo):
        del repo._rebaseset

def _rebasedvisible(orig, repo):
    """ensure rebased revs stay visible (see issue4505)"""
    blockers = orig(repo)
    blockers.update(getattr(repo, '_rebaseset', ()))
    return blockers

def _computeobsoletenotrebased(repo, rebasesetrevs, dest):
    """return a mapping obsolete => successor for all obsolete nodes to be
    rebased that have a successors in the destination

    obsolete => None entries in the mapping indicate nodes with no succesor"""
    obsoletenotrebased = {}

    # Build a mapping successor => obsolete nodes for the obsolete
    # nodes to be rebased
    allsuccessors = {}
    cl = repo.changelog
    for r in rebasesetrevs:
        n = repo[r]
        if n.obsolete():
            node = cl.node(r)
            for s in obsolete.allsuccessors(repo.obsstore, [node]):
                try:
                    allsuccessors[cl.rev(s)] = cl.rev(node)
                except LookupError:
                    pass

    if allsuccessors:
        # Look for successors of obsolete nodes to be rebased among
        # the ancestors of dest
        ancs = cl.ancestors([repo[dest].rev()],
                            stoprev=min(allsuccessors),
                            inclusive=True)
        for s in allsuccessors:
            if s in ancs:
                obsoletenotrebased[allsuccessors[s]] = s
            elif (s == allsuccessors[s] and
                  allsuccessors.values().count(s) == 1):
                # plain prune
                obsoletenotrebased[s] = None

    return obsoletenotrebased

def summaryhook(ui, repo):
    if not os.path.exists(repo.join('rebasestate')):
        return
    try:
        state = restorestatus(repo)[2]
    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')])
    # ensure rebased rev are not hidden
    extensions.wrapfunction(repoview, '_getdynamicblockers', _rebasedvisible)
    revsetpredicate.setup()