Yet another assertion failure when inserting into arrays with JSON_DIAGNOSTICS set

[carlsmedstad]

Inserting into arrays using j_array[index] = value; syntax does not correctly update the parents and will trigger the assertion for parent correctness further down the line.

Please describe the steps to reproduce the issue.

Minimal example:

#define JSON_DIAGNOSTICS 1

#include <nlohmann/json.hpp>

using json = nlohmann::json;


int main() {
  json j_array = json::array();
  j_array[0] = "STRING";
  j_array[1] = "STRING";
  json j_array_copy = j_array;
  return 0;
}

This produces the following assertion error when the copying from j_array to j_array_copy is performed:

assertion_failure: single_include/nlohmann/json.hpp:18670: void nlohmann::basic_json<ObjectType, ArrayType, StringType, BooleanType, NumberIntegerType, NumberUnsignedType, NumberFloatType, AllocatorType, JSONSerializer, BinaryType>::assert_invariant(bool) const [with ObjectType = std::map; ArrayType = std::vector; StringType = std::__cxx11::basic_string<char>; BooleanType = bool; NumberIntegerType = long int; NumberUnsignedType = long unsigned int; NumberFloatType = double; AllocatorType = std::allocator; JSONSerializer = nlohmann::adl_serializer; BinaryType = std::vector<unsigned char>]: Assertion `!check_parents || !is_structured() || std::all_of(begin(), end(), [this](const basic_json & j) { return j.m_parent == this; })' failed.

Which compiler and operating system are you using?

• Compiler: g++ (GCC) 11.1.0
• Operating system: Linux

Which version of the library did you use?

• latest release version 3.10.2
• other release - please state the version: ___
• the develop branch

If you experience a compilation error: can you compile and run the unit tests?

• yes
• no - please copy/paste the error message below

[gregmarr]

Looks like we need a capacity change check at

json/include/nlohmann/json.hpp

Line 3701 in 58b83b7

m_value.array->resize(idx + 1);