I’m using modules with latest CMake and latest MSVC.
Most of this stuff if working nice but I’m having trouble exporting a static constexpr symbol from my class.

This is my simplified setup

#include <array>
namespace foo
{
  class base
  {
    public:
    void foo() {};
    constexpr int doSomthingWithArray();
    private:
      static constexpr std::array m_dummyArray {1u,2u};
  }
    
  constexpr int base::doSomthingWithArray()
  {
   //use m_dummyArray somehow and return some value from array
    return 0;
  }
}

Now in my C++ module i’m exporting this stuff using

// Global module fragment where #includes can happen
module;

#include "base.hpp"

// first thing after the Global module fragment must be a module command
export module my_module;

export
{
  namespace foo
  {
    using ::foo::base;
  }
}

now when i consume this module for example via

#include <gtest/gtest.h>

import my_module;
TEST(Foo,Bar)
{
  base instance;
  instance.foo(); //< works
  base::doSomthingWithArray(); //< produces linker error
}

on the consumer side base::doSomthingWithArray() produces a linker error undefined external symbol m_dummyArray

I’m guessing that m_dummyArray somehow has an internal linakge.

I did try to force external linakge by adding an export to m_dummyArray via

MODULE_EXPORT static constexpr std::array m_dummyArray {1u,2u};

where MODULE_EXPORT only evaluates to export when included in an actual module (and not a regular cpp file) but this produces a compiler error.

Does anybody have an idea on how to fix this?