message: Support serialisation of links
diff: @@ -2049,7 +2049,7 @@ public:
  virtual std::string description() const override
  {
  if (links_exist()) {
  - return m_link_map.description();
  + return m_link_map.description() + metrics::value_separator;
  }
  const Table* target_table = m_link_map.target_table();
  if (target_table && target_table->is_attached()) {
  @@ -3088,12 +3088,14 @@ public:
  virtual std::string description() const override
  {
  + std::string desc = "";
  if (links_exist()) {
  - return m_link_map.description();
  + desc = m_link_map.description() + metrics::value_separator;
  }
  const Table* target_table = m_link_map.target_table();
  if (target_table && target_table->is_attached() && m_column_ndx != npos) {
  - return std::string(target_table->get_column_name(m_column_ndx));
  + desc += std::string(target_table->get_column_name(m_column_ndx));
  + return desc;
  }
  return "";
  }
  