import C++20 module but clang-scan-deps doen't known the "-s USE_WEBGPU=1" options.

[eminor1988]

EMSDK version:

• 3.1.56-asserts

Compile command:

emcmake cmake ${PWD}/../ -G "Ninja" -DCMAKE_BUILD_TYPE="RelWithDebInfo" -DCMAKE_CXX_COMPILER_CLANG_SCAN_DEPS="/root/emsdk/upstream/bin/clang-scan-deps"

Output / Error message:

CMakeFiles/trd-party-lib-dear-imgui.dir/cpp/3rdParty/imgui-1.90.4-docking/imgui_tables.cpp.o.ddi 
"/root/emsdk/upstream/bin/clang-scan-deps" -format=p1689 -- /root/emsdk/upstream/emscripten/em++ -DIMGUI_DEFINE_MATH_OPERATORS -I/home/ubuntu/git/cpp/3rdParty/imgui-1.90.4-docking -I/home/ubuntu/git/cpp/3rdParty/imgui-1.90.4-docking/backends -I/home/ubuntu/git/cpp/3rdParty/imgui-1.90.4-docking/backends/libs -I/home/ubuntu/git/cpp/3rdParty/imgui-1.90.4-docking/examples/libs -O2 -g -DNDEBUG -std=c++23 -s USE_WEBGPU=1 -x c++ /home/ubuntu/git/cpp/3rdParty/imgui-1.90.4-docking/imgui_tables.cpp -c -o CMakeFiles/trd-party-lib-dear-imgui.dir/cpp/3rdParty/imgui-1.90.4-docking/imgui_tables.cpp.o -MT CMakeFiles/trd-party-lib-dear-imgui.dir/cpp/3rdParty/imgui-1.90.4-docking/imgui_tables.cpp.o.ddi -MD -MF CMakeFiles/trd-party-lib-dear-imgui.dir/cpp/3rdParty/imgui-1.90.4-docking/imgui_tables.cpp.o.ddi.d > CMakeFiles/trd-party-lib-dear-imgui.dir/cpp/3rdParty/imgui-1.90.4-docking/imgui_tables.cpp.o.ddi.tmp && mv CMakeFiles/trd-party-lib-dear-imgui.dir/cpp/3rdParty/imgui-1.90.4-docking/imgui_tables.cpp.o.ddi.tmp CMakeFiles/trd-party-lib-dear-imgui.dir/cpp/3rdParty/imgui-1.90.4-docking/imgui_tables.cpp.o.ddi
error: no such file or directory: 'USE_WEBGPU=1'

Expectation:

• I think the dependency scanning process should be able to recognize the compiler option "-s USE_WEBGPU=1", right?

[sbc100]

Does cmake always assume it can pass all cflags to clang-scan-deps?

If so I guess we need an emcc-scan-deps that wraps clang-scan-deps and removes the flags.

In any case I don't think passing -DCMAKE_CXX_COMPILER_CLANG_SCAN_DEPS="/root/emsdk/upstream/bin/clang-scan-deps" is the right thing to do.. if you don't specify CMAKE_CXX_COMPILER_CLANG_SCAN_DEPS at all, what does cmake default to?

[eminor1988]

Sorry for bad English skill...

I am trying to use C++20 module in my project.

I thought emsdk/upstream/bin/clang-scan-deps had already addressed this issue, so I reported it.

Since the code itself relies on <webgpu/webgpu.h> from emscripten, I think it's still necessary to include "-s USE_WEBGPU=1" for clang-scan-deps, but I am not sure.

[sbc100]

The problem is that -sUSE_WEBGPU is an emscripten-specific flag so clang won't understand that.

I guess we need to add some kind of emcc-scan-deps wrapper.

[eminor1988]

related issue:

• CMake 3.28 and C++20, error: CMAKE_CXX_COMPILER_CLANG_SCAN_DEPS-NOTFOUND #22305
• clang-scan-deps is required for CMake 3.28 C++ 20 module support #21042

[Diyou]

USE_WEBGPU is only a link flag. Did you set it explicitly as a compile flag?
I can build simple modules when not setting any emscripten compile flags but clang-scan-deps fails then to find any header in /upstream/emscripten/cache/sysroot/include like emscripten.h or webgpu/webgpu.h

[Diyou]

For some reason /upstream/emscripten/cache/sysroot/include does not get passed to clang-scan-deps by cmake even after include_directories() or target_include_directories().
I tried to pass <emscripten.h> as a precompiled header which results in an error:

[build] "/mnt/e/Workspace/Diyou.Engine/.cache/emsdk/upstream/bin/clang-scan-deps" -format=p1689 -- /mnt/e/Workspace/Diyou.Engine/.cache/emsdk/upstream/emscripten/em++  -I/mnt/e/Workspace/Diyou.Engine/build/Debug.WASM/.cache/SDL3/include -I/mnt/e/Workspace/Diyou.Engine/.cache/SDL3/include -I/mnt/e/Workspace/Diyou.Engine/.cache/SDL3/include/SDL3 -g -std=c++23 -flto=thin -fPIC -idirafter/mnt/e/Workspace/Diyou.Engine/.cache/SDL3/src/video/khronos -Winvalid-pch -Xclang -include-pch -Xclang /mnt/e/Workspace/Diyou.Engine/build/Debug.WASM/CMakeFiles/Diyou.dir/cmake_pch.hxx.pch -Xclang -include -Xclang /mnt/e/Workspace/Diyou.Engine/build/Debug.WASM/CMakeFiles/Diyou.dir/cmake_pch.hxx -x c++ /mnt/e/Workspace/Diyou.Engine/Source/Runtime.c++ -c -o CMakeFiles/Diyou.dir/Source/Runtime.c++.o -MT CMakeFiles/Diyou.dir/Source/Runtime.c++.o.ddi -MD -MF CMakeFiles/Diyou.dir/Source/Runtime.c++.o.ddi.d > CMakeFiles/Diyou.dir/Source/Runtime.c++.o.ddi.tmp && mv CMakeFiles/Diyou.dir/Source/Runtime.c++.o.ddi.tmp CMakeFiles/Diyou.dir/Source/Runtime.c++.o.ddi
[build] Error while scanning dependencies for /mnt/e/Workspace/Diyou.Engine/Source/Runtime.c++:
[build] error: ignore exceptions was enabled in PCH file but is currently disabled
[build] error: PCH file was compiled for the target 'wasm32-unknown-emscripten' but the current translation unit is being compiled for target 'x86_64-unknown-linux-gnu'

[sbc100]

I don't think its going to be easy to make clang-scan-deps works out of the box. There are a bunch of flags you would need to pass to it, most importantly --sysroot=.. and --target=... You might be able do this yourselve by hacking but in the long run we are doing to want and emscripten-specific wrapper around clang-scan-deps I belive.