def do_update_tag
      # query latest count=1 log entry for latest revision; don't attempt to
      # specify revision on the assumption that the requested revision is
      # already checked out. the --revision argument appears to expect a
      # revision from-to range or else a start date or date range or else a
      # specific revision number. it prints nothing when HEAD is specified by
      # itself.
      @repository = @repository.clone
      svn_args = ['log', '--limit', '1']
      svn_client.output_for(svn_args).lines.each do |line|
        if matched = SVN_LOG_REGEX.match(line)
          @repository.tag = matched[1]
          break
        end
      end
    end
def do_update_tag
      # query latest count=1 log entry for latest revision; don't attempt to
      # specify revision on the assumption that the requested revision is
      # already checked out. the --revision argument appears to expect a
      # revision from-to range or else a start date or date range or else a
      # specific revision number. it prints nothing when HEAD is specified by
      # itself.
      @repository = @repository.clone
      svn_args = ['log', '--limit', '1']
      svn_client.output_for(svn_args).lines.each do |line|
        if matched = SVN_LOG_REGEX.match(line)
          @repository.tag = matched[1]
          break
        end
      end
    end
Implements CheckoutBase#do_update_tag