'int' followed by 'void' is illegal

[bjaraujo]

I get following error when trying to link the latest LLVM on Windows (MSVC):

D:\Libraries\LLVM\llvm+clang+lld-20.1.6-x86_64-windows-msvc-release-mt\include\clang\AST\Attrs.inc(6694,24): error C2632: 'int' followed by 'void' is illegal

Attrs.inc(6694,24):
static constexpr int THIS = 0;

I think the name THIS may be conflicting with some reserved macro or keyword on Windows.

[AaronBallman]

This seems to be a compiler error rather than a linker error, and THIS is not a reserved identifier, so this code should work fine. I'm not able to reproduce the issue with Visual Studio 2022 (17.13.7) when building on Windows.

Are you building an unmodified repository or do you have local changes?

We may need you to provide -E output from the source file which includes Attrs.inc and produces an error to have a better idea of what's going on.

[bjaraujo]

This is how I am configuring and building LLVM for Windows:

cmake -S llvm-project/llvm -B llvm-project/build -DCMAKE_BUILD_TYPE=Release -DCMAKE_MSVC_RUNTIME_LIBRARY=MultiThreaded -DLLVM_ENABLE_PROJECTS="llvm;clang;lld"

cmake --build llvm-project/build --config Release

This worked fine in version 19.1.5. but then again there is no line with: static constexpr int THIS = 0; in that version.

If I comment this line out in 20.1.6 it works btw. I believe #undef THIS works too (although the file says to not edit it 😄)

[AaronBallman]

I did some digging and wow, some of Microsoft's platform SDK headers have #define THIS void: basetyps.h and combaseapi.h both have the same macros, along with a bunch of other unreserved identifiers they should not be stealing from the user. And this is trivially easy to demonstrate: https://godbolt.org/z/sP916r1rf

I filed an issue with Microsoft about the problem: https://developercommunity.visualstudio.com/t/basetypsh-and-combaseapih-define-macro/10913912

However, I'm still not seeing the same build issues that you are and neither are any of the bots in our build lab, so I wonder how you're managing to hit this minefield.

[AaronBallman]

Oh well, regardless of how you hit it, I posted a PR to rename things to be less problematic.