Safe way to get changeset. If error occurs show error.

        """

        from kallithea.lib import helpers as h

        try:

            return repo.scm_instance.get_ref_revision(ref_type, ref_name)

        except EmptyRepositoryError as e:

            if returnempty:

                return repo.scm_instance.EMPTY_CHANGESET

            h.flash(h.literal(_('There are no changesets yet')),

                    category='error')

            raise webob.exc.HTTPNotFound()

        except ChangesetDoesNotExistError as e:

                    category='error')

            raise webob.exc.HTTPNotFound()

        except RepositoryError as e:

            log.error(traceback.format_exc())

            h.flash(safe_str(e), category='error')

            raise webob.exc.HTTPBadRequest()

class WSGIResultCloseCallback(object):

    """Wrap a WSGI result and let close call close after calling the

    close method on the result.

    """

                    elif rev.op == 'tag':

                        lbl = _('Created tag: %s') % rev.ref_name

                    else:

                        lbl = 'Unknown operation %s' % rev.op

                else:

                    lazy_cs = True

                    lbl = rev.short_id[:8]

                    url_ = url('changeset_home', repo_name=repo_name,

                               revision=rev.raw_id)

            else:

                # changeset cannot be found - it might have been stripped or removed

                lbl = rev[:12]

            if parse_cs:

                return link_to(lbl, url_, title=title_, class_='tooltip')

            return link_to(lbl, url_, raw_id=rev.raw_id, repo_name=repo_name,

                           class_='lazy-cs' if lazy_cs else '')

        def _get_op(rev_txt):

            _op = None

            _name = rev_txt

            if len(rev_txt.split('=>')) == 2:

                _op, _name = rev_txt.split('=>')

            return _op, _name