Function json_subscript

libbuild2/variable.cxx:2103–2181

  }

  static value
  json_subscript (const value& val, value* val_data,
                  value&& sub,
                  const location& sloc,
                  const location& bloc)
  {
    const json_value* jv (val.null ? nullptr : &val.as<json_value> ());

    // For consistency with other places treat JSON null value as maybe
    // missing array/object. In particular, we don't want to fail trying to
    // lookup by-name on a null value which could have been an object.
    //
    if (jv != nullptr && jv->type == json_type::null)
      jv = nullptr;

    // Process subscript even if the value is null to make sure it is valid.
    //
    bool index;
    uint64_t i (0);
    string   n;

    // Always interpret uint64-typed subscript as index even for objects.
    // This can be used to, for example, to iterate with an index over object
    // members.
    //
    if (!sub.null && sub.type == &value_traits<uint64_t>::value_type)
    {
      i = sub.as<uint64_t> ();
      index = true;
    }
    else
    {
      // How we interpret the subscript depends on the JSON value type. For
      // objects we treat it as a string (member name) and for everything else
      // as an index.
      //
      // What if the value is null and we don't have a JSON type? In this case
      // we treat as a string since a valid number is also a valid string.
      //
      try
      {
        if (jv == nullptr || jv->type == json_type::object)
        {
          n = convert<string> (move (sub));
          index = false;
        }
        else
        {
          i = convert<uint64_t> (move (sub));
          index = true;
        }
      }
      catch (const invalid_argument& e)
      {
        // We will likely be trying to interpret a member name as an integer
        // due to the incorrect value type so issue appropriate diagnostics.
        //
        diag_record dr (fail (sloc));