bash-5.2$ cd Tests/RunCMake/CXXModules/examples/import-std
bash-5.2$ !CXX
CXX=g++-15 cmake -S . -B build --fresh -D CMAKE_CXX_STANDARD_LIBRARY=libstdc++
-- The CXX compiler identification is GNU 15.1.0
-- Checking whether CXX compiler has -isysroot
-- Checking whether CXX compiler has -isysroot - yes
-- Checking whether CXX compiler supports OSX deployment target flag
-- Checking whether CXX compiler supports OSX deployment target flag - yes
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/local/bin/g++-15 - skipped
-- Detecting CXX compile features
CMake Warning (dev) at /Users/clausklein/.local/share/cmake-4.0/Modules/Compiler/CMakeCommonCompilerMacros.cmake:248 (cmake_language):
CMake's support for `import std;` in C++23 and newer is experimental. It
is meant only for experimentation and feedback to CMake developers.
Call Stack (most recent call first):
/Users/clausklein/.local/share/cmake-4.0/Modules/CMakeDetermineCompilerSupport.cmake:113 (cmake_create_cxx_import_std)
/Users/clausklein/.local/share/cmake-4.0/Modules/CMakeTestCXXCompiler.cmake:83 (CMAKE_DETERMINE_COMPILER_SUPPORT)
CMakeLists.txt:4 (project)
This warning is for project developers. Use -Wno-dev to suppress it.
-- Detecting CXX compile features - done
-- Configuring done (1.6s)
-- Generating done (0.0s)
-- Build files have been written to: /Users/clausklein/Downloads/cmake/Tests/RunCMake/CXXModules/examples/import-std/build
bash-5.2$ !ninja
ninja -C build/
ninja: Entering directory `build/'
ninja: error: 'CMakeFiles/__CMAKE__CXX23@synth_db5858ea839d.dir/CXXDependInfo.json', needed by 'CMakeFiles/__CMAKE__CXX23@synth_db5858ea839d.dir/CXX.dd', missing and no known rule to make it
bash-5.2$ ninja -C build/ -v
ninja: Entering directory `build/'
ninja: error: 'CMakeFiles/__CMAKE__CXX23@synth_db5858ea839d.dir/CXXDependInfo.json', needed by 'CMakeFiles/__CMAKE__CXX23@synth_db5858ea839d.dir/CXX.dd', missing and no known rule to make it
bash-5.2$ ninja -C build/ -nv
ninja: Entering directory `build/'
ninja: error: 'CMakeFiles/__CMAKE__CXX23@synth_db5858ea839d.dir/CXXDependInfo.json', needed by 'CMakeFiles/__CMAKE__CXX23@synth_db5858ea839d.dir/CXX.dd', missing and no known rule to make it
it works better it the project is created like this:
cd build
CXX=g++-15 cmake -S .. -B . --fresh
@ben.boeckel Some project cmake file are create at SOURCE_DIR?
bash-5.2$ tree build CMakeFiles/
build
├── CMakeCache.txt
├── CMakeFiles
│ ├── 4.0.20250529-gdf894a1
│ │ ├── CMakeCXXCompiler.cmake
│ │ ├── CMakeDetermineCompilerABI_CXX.bin
│ │ ├── CMakeSystem.cmake
│ │ └── CompilerIdCXX
│ │ ├── CMakeCXXCompilerId.cpp
│ │ ├── a.out
│ │ └── tmp
│ ├── CMakeConfigureLog.yaml
│ ├── CMakeScratch
│ ├── InstallScripts.json
│ ├── TargetDirectories.txt
│ ├── __CMAKE__CXX23@synth_db5858ea839d.dir
│ ├── cmake.check_cache
│ ├── main.dir
│ ├── pkgRedirects
│ └── rules.ninja
├── CTestTestfile.cmake
├── build.ninja
├── cmake_install.cmake
└── compile_commands.json
CMakeFiles/
├── __CMAKE__CXX23@synth_db5858ea839d.dir
│ └── CXXDependInfo.json
└── main.dir
└── CXXDependInfo.json
12 directories, 17 files
bash-5.2$
I found the same problems with clang-20:
bash-5.2$ CXX=clang++ cmake -S . -B build --fresh -D CMAKE_CXX_STANDARD=26 -D CMAKE_CXX_MODULE_STD=OFF
-- The CXX compiler identification is Clang 20.1.5
-- Detecting CXX compiler ABI info
-- Detecting CXX compiler ABI info - done
-- Check for working CXX compiler: /usr/local/opt/llvm/bin/clang++ - skipped
-- Detecting CXX compile features
-- Detecting CXX compile features - done
-- CMAKE_CXX_SCAN_FOR_MODULES="1" ; CMAKE_CXX_MODULE_STD="OFF" ; CMAKE_CXX_COMPILER_IMPORT_STD=""
-- Compiler is: Clang version: 20.1.5
-- CMake is: 4.0.20250529-gdf894a1 modules scan: 1
Cloning into 'catch2-src'...
HEAD is now at 2b60af89 v3.8.1
-- Performing Test HAVE_FLAG__ffile_prefix_map__Users_clausklein_Workspace_cpp_cxx23_scope_build__deps_catch2_src__
-- Performing Test HAVE_FLAG__ffile_prefix_map__Users_clausklein_Workspace_cpp_cxx23_scope_build__deps_catch2_src__ - Success
Examples to be built: scope_example;unique_resource;unique_resource-file
-- Configuring done (12.5s)
-- Generating done (0.2s)
-- Build files have been written to: /Users/clausklein/Workspace/cpp/cxx23/scope/build
bash-5.2$ ninja -C build
ninja: Entering directory `build'
ninja: error: 'CMakeFiles/beman.scope.dir/CXXDependInfo.json', needed by 'CMakeFiles/beman.scope.dir/include/beman/scope/beman.scope.cppm.o.modmap', missing and no known rule to make it
bash-5.2$ tree CMakeFiles/
CMakeFiles/
├── __CMAKE__CXX26@synth_02d7bd95711d.dir
│ └── CXXDependInfo.json
└── beman.scope.dir
└── CXXDependInfo.json
3 directories, 2 files
bash-5.2$
somethings goes wrong on master within Ninja Generator!
snipped of git diff v4.0.2 Source/cmNinjaTargetGenerator.cxx:
diff --git a/Source/cmNinjaTargetGenerator.cxx b/Source/cmNinjaTargetGenerator.cxx
index 8d936525b0..ac87c0d32b 100644
--- a/Source/cmNinjaTargetGenerator.cxx
+++ b/Source/cmNinjaTargetGenerator.cxx
@@ -490,38 +478,20 @@ std::string cmNinjaTargetGenerator::GetPreprocessedFilePath(
std::string const ppName =
cmStrCat(objName.substr(0, objName.size() - objExt.size()), "-pp.", ppExt);
- std::string path = this->LocalGenerator->GetHomeRelativeOutputPath();
- if (!path.empty()) {
- path += '/';
- }
- path +=
- cmStrCat(this->LocalGenerator->GetTargetDirectory(this->GeneratorTarget),
- this->GetGlobalGenerator()->ConfigDirectory(config), '/', ppName);
- return path;
+ return cmStrCat(this->GetObjectFileDir(config), '/', ppName);
}
std::string cmNinjaTargetGenerator::GetDyndepFilePath(
std::string const& lang, std::string const& config) const
{
- std::string path = this->LocalGenerator->GetHomeRelativeOutputPath();
- if (!path.empty()) {
- path += '/';
- }
- path += cmStrCat(
- this->LocalGenerator->GetTargetDirectory(this->GeneratorTarget),
- this->GetGlobalGenerator()->ConfigDirectory(config), '/', lang, ".dd");
- return path;
+ return cmStrCat(this->GetObjectFileDir(config), '/', lang, ".dd");
}
std::string cmNinjaTargetGenerator::GetTargetDependInfoPath(
std::string const& lang, std::string const& config) const
{
- std::string path =
- cmStrCat(this->Makefile->GetCurrentBinaryDirectory(), '/',
- this->LocalGenerator->GetTargetDirectory(this->GeneratorTarget),
- this->GetGlobalGenerator()->ConfigDirectory(config), '/', lang,
- "DependInfo.json");
- return path;
+ return cmStrCat(this->GetObjectFileDir(config), '/', lang,
+ "DependInfo.json");
}
std::string cmNinjaTargetGenerator::GetTargetOutputDir(
``