BUG: Cannot build C++ project using MSVC 2019 due to lapack.h

[larsoner]

Description

Over in OpenBLAS (OpenMathLib/OpenBLAS#3661) they vendor the reference lapack.h. If I take their compiled OpenBLAS lib (or the one that SciPy makes) and try to use it in a C++ project that uses LAPACK (which requires including the OpenBLAS lapack headers, which are really yours I think) and compiling with MSVC 2019, I end up with an error like:

[1/86] Building CXX object OpenMEEGMaths\CMakeFiles\OpenMEEGMaths.dir\src\vector.cpp.obj
FAILED: OpenMEEGMaths/CMakeFiles/OpenMEEGMaths.dir/src/vector.cpp.obj 
C:\PROGRA~2\MICROS~1\2019\ENTERP~1\VC\Tools\MSVC\1429~1.301\bin\Hostx64\x64\cl.exe  /nologo /TP -DH5_BUILT_AS_DYNAMIC_LIB -DHAVE_BLAS -DHAVE_LAPACK -DHAVE_SHARED_PTR_ARRAY_SUPPORT -DOpenMEEGMaths_EXPORTS -DUSE_OPENBLAS -I%SRC_DIR%\OpenMEEGMaths\include -I%SRC_DIR%\build_Release\OpenMEEGMaths -I%SRC_DIR%\build_Release -I%SRC_DIR%\OpenMEEGMaths\OpenMEEGMaths\src -external:I%PREFIX%\Library\include -external:W0 /wd4275 /wd4101 -openmp /MD /O2 /Ob2 /DNDEBUG -std:c++17 /showIncludes /FoOpenMEEGMaths\CMakeFiles\OpenMEEGMaths.dir\src\vector.cpp.obj /FdOpenMEEGMaths\CMakeFiles\OpenMEEGMaths.dir\ /FS -c %SRC_DIR%\OpenMEEGMaths\src\vector.cpp
%PREFIX%\Library\include\lapack.h(104): error C2143: syntax error: missing ',' before '*'
%PREFIX%\Library\include\lapack.h(106): error C2143: syntax error: missing ',' before '*'
... <hundreds of these>

You can see it on conda-forge here for example, where it uses the OpenBLAS libraries that they build:

https://dev.azure.com/conda-forge/feedstock-builds/_build/results?buildId=524975&view=logs&jobId=5be07ae1-d8ba-5406-47b6-8e3a3a12f825&j=5be07ae1-d8ba-5406-47b6-8e3a3a12f825&t=0bf03e01-0bec-5b85-5316-b1633322e895

And on GitHub actions here from earlier this week, same error -- this is using the OpenBLAS builds SciPy makes with mingw64, but I had the same problem when I tried previously just by downloading the 0.3.20 release binaries from GitHub:

Run cmake --build build  --config Release
Microsoft (R) Build Engine version 16.11.2+f32259642 for .NET Framework
Copyright (C) Microsoft Corporation. All rights reserved.
  Checking Build System
  Building Custom Rule D:/a/openmeeg/openmeeg/OpenMEEGMaths/CMakeLists.txt
  vector.cpp
C:\Program Files (x86)\Microsoft Visual Studio\2019\Enterprise\VC\Tools\MSVC\14.16.27023\include\xlocale(319): warning C4[53](https://github.com/openmeeg/openmeeg/runs/6975816876?check_suite_focus=true#step:16:54)0: C++ exception handler used, but unwind semantics are not enabled. Specify /EHsc [D:\a\openmeeg\openmeeg\build\OpenMEEGMaths\OpenMEEGMaths.vcxproj]
d:\a\openmeeg\openmeeg\openblas\64\include\lapack.h(104): error C2143: syntax error: missing ',' before '*' [D:\a\openmeeg\openmeeg\build\OpenMEEGMaths\OpenMEEGMaths.vcxproj]
d:\a\openmeeg\openmeeg\openblas\64\include\lapack.h(106): error C2143: syntax error: missing ',' before '*' [D:\a\openmeeg\openmeeg\build\OpenMEEGMaths\OpenMEEGMaths.vcxproj]
... <hundreds of these>

I am a bit mystified by this because these lines are protected by an ifdef that should take care of this I think:

https://github.com/xianyi/OpenBLAS/blob/9283c7c0b5a9ec7bbe3b6dfc1a019b29b3e112e5/lapack-netlib/LAPACKE/include/lapack.h#L71-L104

Anyone run into this before? Perhaps it's a cmake+MSVC+CPP issue, and there is some cmake fix...? Not sure.

An identical build configuration using mingw64 to build my project doesn't have this problem... but I think for conda-forge I might need to build with MSVC. And in any case it would be nice if it worked...

Checklist

• I've included a minimal example to reproduce the issue
• I'd be willing to make a PR to solve this issue

No minimal example yet but I could make one if it would help. I think it would probably just require using MSVC 2019+ and building a C++ project, but maybe there is more to it!

[larsoner]

FYI I fixed this on MSVC 15 2017 in my project by using:

#if defined(_MSC_VER)
    #include <complex.h>
    #define LAPACK_COMPLEX_CUSTOM
    #define lapack_complex_float _Fcomplex
    #define lapack_complex_double _Dcomplex
#endif

I still need to get MSVC 16 2019 to work with some variant of this change, but I think I should be able to. I'll go ahead and close!