Append mode incompatible with Span Put() API – BP4 and BP5 both affected

[franzpoeschel]

Describe the bug
Trying to use the Span API in an engine opened with Append mode will lead to this error:

terminate called after throwing an instance of 'std::invalid_argument'
  what():  [Wed Jun 07 15:43:29 2023] [ADIOS2 EXCEPTION] <Core> <Engine> <CheckOpenModes> : Engine open mode not valid for  for variable somevariable, in call to Variable<T>::Span Put

To Reproduce

#include <adios2.h>
#include <numeric>

int main(int argsc, char **argsv)
{
    constexpr size_t num_items = 100;
    std::string engine = "bp5";
    std::string filename = "append." + engine;

    // Creating a file with append mode works fine
    {
        adios2::ADIOS adios;
        auto IO = adios.DeclareIO("asdf");
        IO.SetEngine(engine);
        auto engine = IO.Open(filename, adios2::Mode::Append);

        engine.BeginStep();
        {
            auto var = IO.DefineVariable<int>(
                "somevariable", {num_items}, {0}, {num_items});
            std::vector<int> data(num_items);
            std::iota(data.begin(), data.end(), 0);
            engine.Put(var, data.data());
        }
        engine.EndStep();
        engine.Close();
    }

    // Appending to the file with normal Put() works too
    {
        adios2::ADIOS adios;
        auto IO = adios.DeclareIO("asdf");
        IO.SetEngine(engine);
        auto engine = IO.Open(filename, adios2::Mode::Append);

        engine.BeginStep();
        {
            auto var = IO.DefineVariable<int>(
                "somevariable", {num_items}, {0}, {num_items});
            std::vector<int> data(num_items);
            std::iota(data.begin(), data.end(), 0);
            engine.Put(var, data.data());
        }
        engine.EndStep();
        engine.Close();
    }

    // Appending to the file with span Put() will crash
    {
        adios2::ADIOS adios;
        auto IO = adios.DeclareIO("asdf");
        IO.SetEngine(engine);
        auto engine = IO.Open(filename, adios2::Mode::Append);

        engine.BeginStep();
        {
            auto var = IO.DefineVariable<int>(
                "somevariable", {num_items}, {0}, {num_items});
            auto span = engine.Put(var);
            int *ptr = &span[0];
            std::iota(ptr, ptr + num_items, 0);
            engine.EndStep();
        }
        engine.Close();
    }
}

cmake_minimum_required(VERSION 3.12.0)

project(adios2_testing)
find_package(ADIOS2 REQUIRED)

add_executable(main main.cpp)
target_link_libraries(main PRIVATE adios2::cxx11)

Replacing bp5 with bp4 gives the same type of error.

Expected behavior
The open mode verification should recognize the Append mode for Span-based Put.

Desktop (please complete the following information):

• OS/Platform: generic Linux
• Build: Gcc 11.3.0, ADIOS2 v2.9.0

Following up
Was the issue fixed? Please report back.

[eisenhauer]

Looks like a simple oversight. PR submitted.

[franzpoeschel]

Thanks, Greg!

[eisenhauer]

This should be fixed by #3657.