[C++20][Modules] Cannot export a declaration within a linkage-specification

[cpplearner]

Clang rejects the following module unit:

export module mod;

extern "C++" {
    export void f();
}

(https://godbolt.org/z/dPYhGW7ah)

The error message is:

<source>:4:5: error: export declaration can only be used within a module purview
    4 |     export void f();
      |     ^

I think the declaration of f should be considered to be within the purview of module mod, even though it is attached to the global module.

Note that GCC and MSVC accept the above module unit.

Also note that clang seems to permit export extern "C++" { void f(); }.

[llvmbot]

@llvm/issue-subscribers-clang-modules

Author: S. B. Tam (cpplearner)

Clang rejects the following module unit:

export module mod;

extern "C++" {
    export void f();
}

(https://godbolt.org/z/dPYhGW7ah)

The error message is:

<source>:4:5: error: export declaration can only be used within a module purview
    4 |     export void f();
      |     ^

I think the declaration of f should be considered to be within the purview of module mod, even though it is attached to the global module.

Note that GCC and MSVC accept the above module unit.

Also note that clang seems to permit export extern "C++" { void f(); }.

[ChuanqiXu9]

Good catch. Sorry for misreading the wordings of module purview.