# 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 descendant of target ref name

                if not c.is_range and 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

                elif c.pull_request.is_closed():

                    c.update_msg = _('This pull request has been closed and can not be updated.')

                else: # look for descendants of PR head on source branch in org repo

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

                                                             revs[0], c.cs_branch_name)

                    if len(avail_revs) > 1: # more than just revs[0]

                        # also show changesets that not are descendants but would be merged in

                        targethead = other_scm_instance.get_changeset(c.a_branch_name).raw_id

                        if org_scm_instance.path != other_scm_instance.path:

                            # Note: org_scm_instance.path must come first so all

                            # valid revision numbers are 100% org_scm compatible

                            # - both for avail_revs and for revset results

                            hgrepo = unionrepo.unionrepository(org_scm_instance.baseui,

                                                               org_scm_instance.path,

                                                               other_scm_instance.path)

                        else:

                            hgrepo = org_scm_instance._repo

                        show = set(hgrepo.revs('::%ld & !::parents(%s) & !::%s',

                                               avail_revs, revs[0], targethead))

                    else:

                        show = set()

                        avail_revs = set() # drop revs[0]

                        c.update_msg = _('No additional changesets found for iterating on this pull request.')

                    # TODO: handle branch heads that not are tip-most

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

                    if brevs:

                        # also show changesets that are on branch but neither ancestors nor descendants

                        show.update(org_scm_instance._repo.revs('::%ld - ::%ld - ::%s', brevs, avail_revs, c.a_branch_name))

                        show.add(revs[0]) # make sure graph shows this so we can see how they relate

                        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))

                    avail_show = sorted(show, reverse=True)

            elif org_scm_instance.alias == 'git':

                c.cs_repo.scm_instance.get_changeset(c.cs_rev) # check it exists - raise ChangesetDoesNotExistError if not

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

        except ChangesetDoesNotExistError:

            c.update_msg = _('Error: some changesets not found when displaying pull request from %s.') % c.cs_rev

        c.avail_revs = avail_revs

        c.avail_cs = [org_scm_instance.get_changeset(r) for r in avail_show]

          </div>

        </div>

        <div class="form-group">

          <label>${_('Created on')}:</label>

          <div>

              <div>${h.fmt_date(c.pull_request.created_on)}</div>

          </div>

        </div>

        <div class="form-group">

          <label>${_('Owner')}:</label>

          <div class="pr-not-edit">

                  ${h.gravatar_div(c.pull_request.owner.email, size=20)}

                  <span>${c.pull_request.owner.full_name_and_username}</span><br/>

                  <span><a href="mailto:${c.pull_request.owner.email}">${c.pull_request.owner.email}</a></span><br/>

          </div>

          <div class="pr-do-edit" style="display:none">

               ${h.text('owner', class_='form-control', value=c.pull_request.owner.username, placeholder=_('Type name of user'))}

          </div>

        </div>

        <div class="form-group">

          <label>${_('Next iteration')}:</label>

            <div>

              <p>${c.update_msg}</p>

              <div id="updaterevs" class="clearfix">

                <div id="updaterevs-graph">

                  <canvas id="avail_graph_canvas"></canvas>

                </div>

                <table class="table" id="updaterevs-table">

                  %for cnt, cs in enumerate(c.avail_cs):

                    <tr id="chg_available_${cnt+1}" class="${'mergerow' if len(cs.parents) > 1 and not (editable and cs.revision in c.avail_revs) else ''}">

                      %if c.cs_ranges and cs.revision == c.cs_ranges[-1].revision:

                        %if editable:

                        <td>

                            ${h.radio(name='updaterev', value='', checked=True)}

                        </td>

                        %endif

                        <td colspan="4"><span>${_("Current revision - no change")}</span></td>

                      %else:

                        %if editable:

                        <td>

                          ${h.radio(name='updaterev', value=cs.raw_id, style=None if cs.revision in c.avail_revs else 'visibility: hidden')}

                        </td>

                        %endif

                        <td><span data-toggle="tooltip" title="${h.age(cs.date)}">${cs.date}</span></td>

                        <td>${h.link_to(h.show_id(cs),h.url('changeset_home',repo_name=c.cs_repo.repo_name,revision=cs.raw_id), class_='changeset_hash')}</td>

                        <td>

                          <div class="pull-right">