other_scm_instance = c.other_repo.scm_instance

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

            if c.org_ref_type != 'branch':

                c.org_branch_name = org_scm_instance.get_changeset(c.org_ref_name).branch # use ref_type ?

            other_branch_name = c.other_ref_name

            if c.other_ref_type != 'branch':

                other_branch_name = other_scm_instance.get_changeset(c.other_ref_name).branch # use ref_type ?

            # 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, other_branch_name):

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

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

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

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

                if arevs:

                    if c.pull_request.is_closed():

                        c.update_msg = _('This pull request has been closed and can not be updated with descendent changes on %s:') % c.org_branch_name

                    else:

                        c.update_msg = _('This pull request can be updated with descendent changes on %s:') % c.org_branch_name

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

                else:

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

            else:

                c.update_msg_other = _('Branch %s does not contain other changes.') % c.org_branch_name

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

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

        c.statuses = c.org_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.other_rev, c.org_rev, org_scm_instance.path))

        txtdiff = org_scm_instance.get_diff(rev1=safe_str(c.other_rev), rev2=safe_str(c.org_rev),

                                      ignore_whitespace=ignore_whitespace,

                                      context=line_context)

        diff_processor = diffs.DiffProcessor(txtdiff or '', format='gitdiff',

                                             diff_limit=diff_limit)

        _parsed = diff_processor.prepare()