Build Host: Fedora 31
Target: Fedora 31 (Linux)
Build System: CMake
Toolchains: gcc-9 c++11, clang-9 c++14
Branch: develop

Synopsys
Misuse of RapidJSON public interface results in internal assertion in RapidJSON library

Steps to Reproduce

$ cmake -DCMAKE_BUILD_TYPE=Debug ...
build the project as normal
$ bench <source_root>/bench/data/canada.json

Detail

The problem can be isolated to the benchmark enabled by
vi.emplace_back(new rapidjson_crt_impl); in function main of bench.cpp

The parse member function of the benchmark contains the following lines:

            CrtAllocator alloc;
            GenericDocument<
                UTF8<>, CrtAllocator> d(&alloc);
            d.Clear();  <<<--- PROBLEM IS HERE

In RapidJSON, the implementation of GenericDocument<>::Clear() executes an assertion that the internal value representing the document is an Array:

    void Clear() {
        RAPIDJSON_ASSERT(IsArray()); 
        GenericValue* e = GetElementsPointer();
        for (GenericValue* v = e; v != e + data_.a.size; ++v)
            v->~GenericValue();
        data_.a.size = 0;
    }

In the above use pattern, the document is not an Array, as it has not been initialised at all. It is actually null.

The assertion fails, resulting in either SEGFAULT of a debugger break.

Solution

remove the line d.Clear();

Side Effects of Solution

None. The document is re-created each time around the loop in any case.