[MSVC][/std:c++latest][module] error C2065: 'oops_detail_namespace_is_visible': undeclared identifier

[QuellaZhang]

Hi All,

I found the follow error when I build the latest source code of Fmt on MSVC with /std:c++latest and module enable, can you help confirm? I used VS2019 16.11.5.

Build steps:

1. git clone https://github.com/fmtlib/fmt.git fmt
2. cd fmt
3. enable module test on https://github.com/fmtlib/fmt/blob/master/CMakeLists.txt#L89
4. mkdir build && cd build
5. cmake -G "Visual Studio 16 2019" -DCMAKE_BUILD_TYPE=Release -A x64 -DCMAKE_CXX_STANDARD=20 ..
6. cmake --build . --config Release --verbose -- /maxcpucount

Build log: fmt_build.log

Error info:
F:\build\fmt\test\module-test.cc(87,11): error C2065: 'oops_detail_namespace_is_visible': undeclared identifier.

[vitaut]

I don't think modules work in MSVC 2019 (or at least some versions of it). cc @DanielaE

[DanielaE]

Modules work since msvc 16.10 with increasing conformance to the C++20 specification. None of the deviations are functionally relevant in client code, but they are tested for.

[vitaut]

I'm always confused by their versioning =D