If you are interested in C++20 modules support in CMake, please have a look at this blog post:
[https://www.kitware.com/import-cmake-c20-modules/](https://www.kitware.com/import-cmake-c20-modules/)
It would be great to get feedback from users on this work.
Thanks.
-Bill
---
This is great, thank you for putting all the info in one place!
I have been dabbling for some time with modules with Vs2022 and CMake!
I was wondering does this mean that those instructions are generator agnostic? I ask because it is not mentioned and I wonder if I can now use ninja on windows with modules.
Thank you again!
---
> [@monamimani](#):
>
> I ask because it is not mentioned and I wonder if I can now use ninja on windows with modules.
Yes, that is tested and should work.
---
> [@neundorf](#):
>
> Since the article mentions ninja explicitely, what about make ?
No support yet. No plan either.
Edited to add: I should clarify that `Makefile` support would be good, we just have no concrete plans at the moment.
---
Hi, I was trying to use the ninja generator (with MSVC) and C++ module and following the blog post, but something is wrong.
Maybe it is a bug with Visual Studio, but the CMake bundled with Visual Studio doesn’t recognize **CXX\_MODULES** for **FILE\_SET**.
When I generate, I get
> target\_sources File set TYPE may only be “HEADERS”
I verified the CMake version that is bundled with visual studio and its
> cmake version 3.25.2-msvc4
Should I open a bug? or am I missing something?
---
Another thing to add to the post would be that the target\_source should not be an executable, as it will refuse the FILESET. At least that is my understanding so far. I have opened an issues with CMake and vcpkg ( the error is coming from vcpkg.cmake). I was using CMake 3.26.0-rc4
---
> [@monamimani](#):
>
> the target\_source should not be an executable, as it will refuse the FILESET
I see you opened [CMake Issue 24537](https://gitlab.kitware.com/cmake/cmake/-/issues/24537) for that, but it just isn’t true. Something else is going wrong with your attempt to try this feature.
> [@scivision](#):
>
> documentation is incorrect for saying CMake 3.25.
CMake 3.25.2 should work, but needs a [different `CMAKE_EXPERIMENTAL_CXX_MODULE_CMAKE_API`](https://gitlab.kitware.com/cmake/cmake/-/blob/v3.25.2/Help/dev/experimental.rst#c-20-module-apis) value.
---
Hey,
### Problem
I was trying to run simple project with C++20 modules with CMake but I get the following compilation error from ninja:
```auto
missing compilation database and failed to contruct one by --p1689-targeted-file-name, --p1689-targeted-output
```
Do you see where is the issue?
### Details
I pushed the project here: [Files · 9f9346c41795a14f18266c727fa3621d4be9ccba · WRCIECH / cpp-20-modules-with-cmake-and-clang · GitLab](https://gitlab.com/WRCIECH/cpp-20-modules-with-cmake-and-clang/-/tree/9f9346c41795a14f18266c727fa3621d4be9ccba)
CMake and Ninja version:
```auto
cmake --version
cmake version 3.26.0-rc5
ninja --version
1.11.1
```
The full error after typing `cmake --build --preset=macos`:
```auto
[1/8] Scanning /Users/wojciech/dev/private/test_modules/cpp-20-modules-with-cmake-and-clang/main.cxx for CXX dependencies
FAILED: CMakeFiles/hello.dir/main.cxx.o.ddi CMakeFiles/hello.dir/main.cxx.o.modmap
/Users/wojciech/dev/private/test_modules/llvm/build/bin/clang-scan-deps -format=p1689 -- /Users/wojciech/dev/private/test_modules/llvm/build/bin/clang++ -std=c++20 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk -x c++ /Users/wojciech/dev/private/test_modules/cpp-20-modules-with-cmake-and-clang/main.cxx -c -o CMakeFiles/hello.dir/main.cxx.o -MT CMakeFiles/hello.dir/main.cxx.o.ddi -MD -MF CMakeFiles/hello.dir/main.cxx.o.ddi.d > CMakeFiles/hello.dir/main.cxx.o.ddi
missing compilation database and failed to contruct one by --p1689-targeted-file-name, --p1689-targeted-output
[2/8] Scanning /Users/wojciech/dev/private/test_modules/cpp-20-modules-with-cmake-and-clang/foo.cxx for CXX dependencies
FAILED: CMakeFiles/foo.dir/foo.cxx.o.ddi CMakeFiles/foo.dir/foo.cxx.o.modmap
/Users/wojciech/dev/private/test_modules/llvm/build/bin/clang-scan-deps -format=p1689 -- /Users/wojciech/dev/private/test_modules/llvm/build/bin/clang++ -std=c++20 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk -x c++ /Users/wojciech/dev/private/test_modules/cpp-20-modules-with-cmake-and-clang/foo.cxx -c -o CMakeFiles/foo.dir/foo.cxx.o -MT CMakeFiles/foo.dir/foo.cxx.o.ddi -MD -MF CMakeFiles/foo.dir/foo.cxx.o.ddi.d > CMakeFiles/foo.dir/foo.cxx.o.ddi
missing compilation database and failed to contruct one by --p1689-targeted-file-name, --p1689-targeted-output
ninja: build stopped: subcommand failed.
```
---