I am trying to build some C++ code in the GitHub CI. This works for GCC and Clang, but compilation with MSVC fails in very weird ways.

The very first error is found at:

template <bool constant, bool nothrow, typename R, typename... Args>
struct Function_Ref_Base {
public:
    using Function = R(Args...) noexcept(nothrow);
    using Storage = const_if_t<void, constant>;
    using Invoker = R(Storage*, Args...) noexcept(nothrow); // <<< error here

... which is:

function_ref.hpp(36,51): error C2065: 'nothrow': undeclared identifier [D:\a\ulight\ulight\build\ulight.vcxproj]
  (compiling source file '../src/main/cpp/cpp.cpp')

Complete nonsense. The full compilation command is:

C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.43.34808\bin\HostX64\x64\CL.exe
  /c /ID:\a\ulight\ulight\include /nologo
  /W4 /WX-
  /diagnostics:column
  /O2 /Ob2
  /D _MBCS /D WIN32 /D _WINDOWS /D NDEBUG /D "CMAKE_INTDIR=\"Release\""
  /EHsc /MD /GS
  /fp:precise /Zc:wchar_t /Zc:forScope /Zc:inline
  /std:c++latest
  /Fo"ulight.dir\Release\\"
  /Fd"D:\a\ulight\ulight\build\Release\ulight.pdb"
  /external:W4 /Gd /TP /errorReport:queue
  D:\a\ulight\ulight\src\main\cpp\chars.cpp
  D:\a\ulight\ulight\src\main\cpp\cpp.cpp
  D:\a\ulight\ulight\src\main\cpp\lua.cpp
  D:\a\ulight\ulight\src\main\cpp\mmml.cpp
  D:\a\ulight\ulight\src\main\cpp\parse_utils.cpp
  D:\a\ulight\ulight\src\main\cpp\ulight.cpp

According to CMake's output, the compiler is:

-- Building for: Visual Studio 17 2022
-- The C compiler identification is MSVC 19.43.34808.0
-- The CXX compiler identification is MSVC 19.43.34808.0

This seems more up-to-date than the latest version available on Compiler Explorer. Despite that, I cannot reproduce the issue there.

Why would I get these bogus errors? The full log is at

I am trying to build some C++ code in the GitHub CI. This works for GCC and Clang, but compilation with MSVC fails in very weird ways.

The very first error is found at:

template <bool constant, bool nothrow, typename R, typename... Args>
struct Function_Ref_Base {
public:
    using Function = R(Args...) noexcept(nothrow);
    using Storage = const_if_t<void, constant>;
    using Invoker = R(Storage*, Args...) noexcept(nothrow); // <<< error here

... which is:

function_ref.hpp(36,51): error C2065: 'nothrow': undeclared identifier [D:\a\ulight\ulight\build\ulight.vcxproj]
  (compiling source file '../src/main/cpp/cpp.cpp')

Complete nonsense. The full compilation command is:

C:\Program Files\Microsoft Visual Studio\2022\Enterprise\VC\Tools\MSVC\14.43.34808\bin\HostX64\x64\CL.exe
  /c /ID:\a\ulight\ulight\include /nologo
  /W4 /WX-
  /diagnostics:column
  /O2 /Ob2
  /D _MBCS /D WIN32 /D _WINDOWS /D NDEBUG /D "CMAKE_INTDIR=\"Release\""
  /EHsc /MD /GS
  /fp:precise /Zc:wchar_t /Zc:forScope /Zc:inline
  /std:c++latest
  /Fo"ulight.dir\Release\\"
  /Fd"D:\a\ulight\ulight\build\Release\ulight.pdb"
  /external:W4 /Gd /TP /errorReport:queue
  D:\a\ulight\ulight\src\main\cpp\chars.cpp
  D:\a\ulight\ulight\src\main\cpp\cpp.cpp
  D:\a\ulight\ulight\src\main\cpp\lua.cpp
  D:\a\ulight\ulight\src\main\cpp\mmml.cpp
  D:\a\ulight\ulight\src\main\cpp\parse_utils.cpp
  D:\a\ulight\ulight\src\main\cpp\ulight.cpp

According to CMake's output, the compiler is:

-- Building for: Visual Studio 17 2022
-- The C compiler identification is MSVC 19.43.34808.0
-- The CXX compiler identification is MSVC 19.43.34808.0

This seems more up-to-date than the latest version available on Compiler Explorer. Despite that, I cannot reproduce the issue there.

Why would I get these bogus errors? The full log is at https://github/Eisenwave/ulight/actions/runs/14104181487/job/39506850293

• c++
• visual-c++
• c++23
• compiler-bug

• 1 Compile fine here – Jarod42 Commented Mar 27 at 10:43
• @Jarod42 minimal repro is in the answer now. – Jan Schultke Commented Mar 27 at 16:03
• I can have msvc ICE by removing added pointer Demo – Jarod42 Commented Mar 27 at 16:54

1 Answer 1

While there are quite a few issues in the build, the most nonsensical message turned out to be a compiler bug (see report), with the following insane minimal reproducible example (https://godbolt./z/oYrr9oehG):

template <bool nothrow>
struct S {
    // error C2065: 'nothrow': undeclared identifier
    using type = int(void*) noexcept(nothrow);
    type* member;
};

void f() {
    S<false> s;
    auto p = s.member;
}

Note that S in the example is Function_Ref_Base in the original.

The remaining messages are related to C++23 features that are not supported by MSVC yet, so I consider this issue solved.