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=pull_request_id),

                  old_pull_request.title)]

        if lost:

            infos.append(_('Missing changesets since the previous version:'))

            for r in old_pull_request.revisions:

                if r in lost:

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

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

        if new_revisions:

            infos.append(_('New changesets on %s %s since the previous version:') % (org_ref_type, org_ref_name))

            for r in reversed(revisions):

                if r in new_revisions:

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

            if ancestor_rev == other_rev:

                                 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:

        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)

        reviewers = [r.user_id for r in old_pull_request.reviewers]

        try:

            old_title, old_v = re.match(r'(.*)\(v(\d+)\)\s*$', old_pull_request.title).groups()

            v = int(old_v) + 1

        except (AttributeError, ValueError):

            old_title = old_pull_request.title

            v = 2

        title = '%s (v%s)' % (old_title.strip(), v)

        description = (old_pull_request.description.rstrip() +

                       '\n'.join(infos))

        try:

            pull_request = PullRequestModel().create(

                self.authuser.user_id,

                old_pull_request.org_repo.repo_name, new_org_ref,