[C++20] [Modules] unresolved external symbol for export __declspec(dllexport) variables from DLL

[huangqinjin]

Steps to Reproduce

hello.cppm

export module hello;

export __declspec(dllexport) int x = 0;

main.cpp

import hello;

int main()
{
    return x;
}

commands

clang++ -std=c++20 -fmodule-output -shared hello.cppm -o hello.dll
clang++ -std=c++20 -fprebuilt-module-path=. main.cpp -L. -lhello

error LNK2019: unresolved external symbol "int x" (?x@@3HA) referenced in function main

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: None (huangqinjin)

### Steps to Reproduce

hello.cppm

export module hello;

export __declspec(dllexport) int x = 0;

main.cpp

import hello;

int main()
{
    return x;
}

commands

clang++ -std=c++20 -fmodule-output -shared hello.cppm -o hello.dll
clang++ -std=c++20 -fprebuilt-module-path=. main.cpp -L. -lhello

error LNK2019: unresolved external symbol "int x" (?x@@<!-- -->3HA) referenced in function main

[ChuanqiXu9]

While I can't test this in windows, I am wondering if you can try:

__declspec(dllexport) export  int x = 0;

[huangqinjin]

While I can't test this in windows, I am wondering if you can try:

__declspec(dllexport) export  int x = 0;

This results in compile error expected unqualified-id.

[ChuanqiXu9]

Thanks for testing. It looks like it is something deeper.