org_repo = RepoModel()._get_repo(old_pull_request.org_repo.repo_name)

        org_ref_type, org_ref_name, org_rev = old_pull_request.org_ref.split(':')

        new_org_rev = self._get_ref_rev(org_repo, 'rev', updaterev)

        other_repo = RepoModel()._get_repo(old_pull_request.other_repo.repo_name)

        other_ref_type, other_ref_name, other_rev = old_pull_request.other_ref.split(':') # other_rev is ancestor

        #assert other_ref_type == 'branch', other_ref_type # TODO: what if not?

        new_other_rev = self._get_ref_rev(other_repo, other_ref_type, other_ref_name)

        cs_ranges, _cs_ranges_not, ancestor_rev = CompareController._get_changesets(org_repo.scm_instance.alias,

            other_repo.scm_instance, new_other_rev, # org and other "swapped"

            org_repo.scm_instance, new_org_rev)

        old_revisions = set(old_pull_request.revisions)

        revisions = [cs.raw_id for cs in cs_ranges]

        new_revisions = [r for r in revisions if r not in old_revisions]

        lost = old_revisions.difference(revisions)

        infos = ['This is an update of %s "%s".' %

                 (h.canonical_url('pullrequest_show', repo_name=old_pull_request.other_repo.repo_name,

                      pull_request_id=old_pull_request.pull_request_id),

                  old_pull_request.title)]

        if lost:

            for r in old_pull_request.revisions:

                if r in lost:

                    rev_desc = org_repo.get_changeset(r).message.split('\n')[0]

                    infos.append('  %s "%s"' % (h.short_id(r), rev_desc))

        if new_revisions:

            for r in reversed(revisions):

                if r in new_revisions:

                    rev_desc = org_repo.get_changeset(r).message.split('\n')[0]

                    infos.append('  %s %s' % (h.short_id(r), h.shorter(rev_desc, 80)))

            if ancestor_rev == other_rev:

                infos.append(_("Ancestor didn't change - show diff since previous version:"))

                infos.append(h.canonical_url('compare_url',

                                 repo_name=org_repo.repo_name, # other_repo is always same as repo_name

                                 org_ref_type='rev', org_ref_name=h.short_id(org_rev), # use old org_rev as base

                                 other_ref_type='rev', other_ref_name=h.short_id(new_org_rev),

                                 )) # note: linear diff, merge or not doesn't matter

            else:

                infos.append(_('This pull request is based on another %s revision and there is no simple diff.') % other_ref_name)

        else:

           infos.append(_('No changes found on %s %s since previous version.') % (org_ref_type, org_ref_name))

           # TODO: fail?

        # hack: ancestor_rev is not an other_ref but we want to show the

        # requested destination and have the exact ancestor

        new_other_ref = '%s:%s:%s' % (other_ref_type, other_ref_name, ancestor_rev)

        new_org_ref = '%s:%s:%s' % (org_ref_type, org_ref_name, new_org_rev)

        try:

            text=_('Closed, replaced by %s .') % h.canonical_url('pullrequest_show',

                                                   repo_name=old_pull_request.other_repo.repo_name,

                                                   pull_request_id=pull_request.pull_request_id),

            repo=old_pull_request.other_repo.repo_id,

            user=c.authuser.user_id,

            pull_request=old_pull_request.pull_request_id,

            closing_pr=True)

        PullRequestModel().close_pull_request(old_pull_request.pull_request_id)

        Session().commit()

        h.flash(_('Pull request update created'),

                category='success')

        return redirect(pull_request.url())

    # pullrequest_post for PR editing

    @LoginRequired()

    @NotAnonymous()

    @HasRepoPermissionAnyDecorator('repository.read', 'repository.write',

                                   'repository.admin')

    def post(self, repo_name, pull_request_id):

        pull_request = PullRequest.get_or_404(pull_request_id)

        if pull_request.is_closed():

            raise HTTPForbidden()

        #only owner or admin can update it

        owner = pull_request.author.user_id == c.authuser.user_id

        repo_admin = h.HasRepoPermissionAny('repository.admin')(c.repo_name)

        if not (h.HasPermissionAny('hg.admin') or repo_admin or owner):

            raise HTTPForbidden()

        _form = PullRequestPostForm()().to_python(request.POST)

        reviewers_ids = [int(s) for s in _form['review_members']]

        if _form['updaterev']:

            return self.create_update(pull_request,

                                      _form['updaterev'],

                                      _form['pullrequest_title'],

                                      _form['pullrequest_desc'],

                                      reviewers_ids)

        old_description = pull_request.description

        pull_request.title = _form['pullrequest_title']

        pull_request.description = _form['pullrequest_desc'].strip() or _('No description')

        PullRequestModel().mention_from_description(pull_request, old_description)

        PullRequestModel().update_reviewers(pull_request_id, reviewers_ids)

        Session().commit()

        c.cs_ranges = [org_scm_instance.get_changeset(x) for x in c.pull_request.revisions]

        c.cs_ranges_org = None # not stored and not important and moving target - could be calculated ...

        revs = [ctx.revision for ctx in reversed(c.cs_ranges)]

        c.jsdata = json.dumps(graph_data(org_scm_instance, revs))

        arevs = []

        c.cs_branch_name = c.cs_ref_name

        other_scm_instance = c.a_repo.scm_instance

        c.update_msg = ""

        c.update_msg_other = ""

        if org_scm_instance.alias == 'hg' and c.a_ref_name != 'ancestor':

            if c.cs_ref_type != 'branch':

                c.cs_branch_name = org_scm_instance.get_changeset(c.cs_ref_name).branch # use ref_type ?

            c.a_branch_name = c.a_ref_name

            if c.a_ref_type != 'branch':

                try:

                    c.a_branch_name = other_scm_instance.get_changeset(c.a_ref_name).branch # use ref_type ?

                except EmptyRepositoryError:

                    c.a_branch_name = 'null' # not a branch name ... but close enough

            # candidates: descendants of old head that are on the right branch

            #             and not are the old head itself ...

            #             and nothing at all if old head is a descendent of target ref name

            if other_scm_instance._repo.revs('present(%s)::&%s', c.cs_ranges[-1].raw_id, c.a_branch_name):

                c.update_msg = _('This pull request has already been merged to %s.') % c.a_branch_name

                arevs = org_scm_instance._repo.revs('%s:: & branch(%s) - %s',

                                                    revs[0], c.cs_branch_name, revs[0])

                if arevs:

                    arevs = sorted(arevs, reverse=True)

                else:

                    c.update_msg = _('No changesets found for updating this pull request.')

            brevs = org_scm_instance._repo.revs('%s - %d - %ld', c.cs_branch_name, revs[0], arevs)

            if brevs:

                c.update_msg_other = _('Note: Branch %s has another head: %s.') % (c.cs_branch_name,

                    h.short_id(org_scm_instance.get_changeset((max(brevs))).raw_id))

        elif org_scm_instance.alias == 'git':

            c.update_msg = _("Git pull requests don't support updates yet.")

        c.available = [org_scm_instance.get_changeset(r) for r in arevs]

        raw_ids = [x.raw_id for x in c.cs_ranges]

        c.cs_comments = c.cs_repo.get_comments(raw_ids)

        c.statuses = c.cs_repo.statuses(raw_ids)

        ignore_whitespace = request.GET.get('ignorews') == '1'

        line_context = request.GET.get('context', 3)

        c.ignorews_url = _ignorews_url

        c.context_url = _context_url

        c.fulldiff = request.GET.get('fulldiff')

        diff_limit = self.cut_off_limit if not c.fulldiff else None

        # we swap org/other ref since we run a simple diff on one repo

        log.debug('running diff between %s and %s in %s'

                  % (c.a_rev, c.cs_rev, org_scm_instance.path))