I see this strange error when I try to build with an installed CXX_MODULES,
The installed module was build with:
# CMake requires the language standard to be specified as compile feature
# when a target provides C++23 modules and the target will be installed
target_compile_features(Algo PUBLIC cxx_std_23)
bash-5.3$ make
cmake --workflow --preset dev
Executing workflow step 1 of 4: configure preset "dev"
-- use ccache
-- CXXFLAGS=-stdlib=libc++
'brew' '--prefix' 'llvm'
-- LLVM_DIR=/usr/local/Cellar/llvm/21.1.8
-- CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES=/usr/local/Cellar/llvm/21.1.8/include/c++/v1;/usr/local/Cellar/llvm/21.1.8/lib/clang/21/include;/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include
-- CMAKE_CXX_STDLIB_MODULES_JSON=/usr/local/Cellar/llvm/21.1.8/lib/c++/libc++.modules.json
-- CMAKE_CXX_COMPILER_IMPORT_STD=23;26
-- CMAKE_CXX_MODULE_STD=ON
-- ALGO_USE_MODULES=ON
CMake Warning (dev) at example/CMakeLists.txt:38 (add_test):
uninitialized variable 'CMAKE_TOOLCHAIN_FILE'
This warning is for project developers. Use -Wno-dev to suppress it.
-- Configuring done (0.2s)
CMake Warning (dev) in CMakeLists.txt:
CMake's support for `import std;` in C++23 and newer is experimental. It
is meant only for experimentation and feedback to CMake developers.
This warning is for project developers. Use -Wno-dev to suppress it.
-- Generating done (0.0s)
-- Build files have been written to: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev
Executing workflow step 2 of 4: build preset "dev"
[3/4] Install the project...
-- Install configuration: "Release"
-- Up-to-date: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/lib/libAlgo.dylib
-- Up-to-date: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/lib/cmake/my_package/modules/algo-interface.cppm
-- Up-to-date: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/include/algo_export.h
-- Up-to-date: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/lib/cmake/my_package/bmi-Clang_Release/algo.pcm
-- Up-to-date: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/lib/cmake/my_package/my_package-targets.cmake
-- Up-to-date: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/lib/cmake/my_package/my_package-targets-release.cmake
-- Up-to-date: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/lib/cmake/my_package/./cxx-modules-my_package-targets.cmake
-- Up-to-date: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/lib/cmake/my_package/./cxx-modules-my_package-targets-Release.cmake
-- Installing: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/lib/cmake/my_package/./target-Algo-Release.cmake
-- Up-to-date: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/lib/cmake/my_package/my_package-config-version.cmake
-- Up-to-date: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/stagedir/lib/cmake/my_package/my_package-config.cmake
Executing workflow step 3 of 4: test preset "dev"
Test project /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev
Start 3: find-package-test
Start 1: app-tests
Start 2: install-to-stagedir
1/3 Test #1: app-tests ........................ Passed 0.01 sec
2/3 Test #2: install-to-stagedir .............. Passed 0.02 sec
3/3 Test #3: find-package-test ................***Failed 3.11 sec
Internal cmake changing into directory: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev/example/find-package-test
======== CMake output ======
use ccache
CXXFLAGS=-stdlib=libc++
'brew' '--prefix' 'llvm'
LLVM_DIR=/usr/local/Cellar/llvm/21.1.8
CMAKE_CXX_IMPLICIT_INCLUDE_DIRECTORIES=/usr/local/Cellar/llvm/21.1.8/include/c++/v1;/usr/local/Cellar/llvm/21.1.8/lib/clang/21/include;/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include
CMAKE_CXX_STDLIB_MODULES_JSON=/usr/local/Cellar/llvm/21.1.8/lib/c++/libc++.modules.json
CMAKE_CXX_COMPILER_IMPORT_STD=23;26
CMAKE_CXX_MODULE_STD=ON
ALGO_USE_MODULES=ON
Configuring done (0.2s)
CMake Warning (dev) in CMakeLists.txt:
CMake's support for `import std;` in C++23 and newer is experimental. It
is meant only for experimentation and feedback to CMake developers.
This warning is for project developers. Use -Wno-dev to suppress it.
Generating done (0.0s)
Build files have been written to: /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev/example/find-package-test
======== End CMake output ======
Change Dir: '/Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev/example/find-package-test'
Run Clean Command: /Users/clausklein/.local/bin/ninja clean
[1/1] Cleaning all built files...
Cleaning... 26 files.
Run Build Command(s): /Users/clausklein/.local/bin/ninja
[1/15] Scanning /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev/stagedir/lib/cmake/my_package/modules/algo-interface.cppm for CXX dependencies
warning: argument unused during compilation: '-c'
[2/15] Scanning /usr/local/Cellar/llvm/21.1.8/share/libc++/v1/std.compat.cppm for CXX dependencies
[3/15] Scanning /usr/local/Cellar/llvm/21.1.8/share/libc++/v1/std.compat.cppm for CXX dependencies
[4/15] Scanning /usr/local/Cellar/llvm/21.1.8/share/libc++/v1/std.cppm for CXX dependencies
[5/15] Scanning /usr/local/Cellar/llvm/21.1.8/share/libc++/v1/std.cppm for CXX dependencies
[6/15] Generating CXX dyndep file CMakeFiles/__cmake_cxx23.dir/CXX.dd
[7/15] Generating CXX dyndep file CMakeFiles/__cmake_cxx26.dir/CXX.dd
[8/15] Generating CXX dyndep file 'CMakeFiles/my_package__Algo@synth_e074a15ef2ea.dir/CXX.dd'
[9/15] Scanning /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/example/main.cpp for CXX dependencies
[10/15] Generating CXX dyndep file CMakeFiles/app.dir/CXX.dd
[11/17] Building CXX object CMakeFiles/__cmake_cxx26.dir/usr/local/Cellar/llvm/21.1.8/share/libc++/v1/std.cppm.o
[12/17] Building CXX object CMakeFiles/__cmake_cxx23.dir/usr/local/Cellar/llvm/21.1.8/share/libc++/v1/std.cppm.o
[13/17] Building CXX object CMakeFiles/__cmake_cxx26.dir/usr/local/Cellar/llvm/21.1.8/share/libc++/v1/std.compat.cppm.o
[14/17] Building CXX object 'CMakeFiles/my_package__Algo@synth_e074a15ef2ea.dir/c42227a90345.bmi'
FAILED: [code=1] CMakeFiles/my_package__Algo@synth_e074a15ef2ea.dir/c42227a90345.bmi
/usr/local/Cellar/llvm/21.1.8/bin/clang++ -DHAS_IMPORT_STD -I/usr/local/Cellar/llvm/21.1.8/include -I/usr/local/Cellar/llvm/21.1.8/include/c++/v1 -I/usr/local/Cellar/llvm/21.1.8/lib/clang/21/include -I/Library/Developer/CommandLineTools/SDKs/MacOSX14.sdk/usr/include -isystem /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev/stagedir/include -stdlib=libc++ -O3 -DNDEBUG -std=gnu++23 -fPIC -stdlib=libc++ --precompile -MD -MT 'CMakeFiles/my_package__Algo@synth_e074a15ef2ea.dir/c42227a90345.bmi' -MF CMakeFiles/my_package__Algo@synth_e074a15ef2ea.dir/c42227a90345.bmi.d @CMakeFiles/my_package__Algo@synth_e074a15ef2ea.dir/c42227a90345.bmi.modmap -fmodules-reduced-bmi -o 'CMakeFiles/my_package__Algo@synth_e074a15ef2ea.dir/c42227a90345.bmi' -c /Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev/stagedir/lib/cmake/my_package/modules/algo-interface.cppm
clang++: warning: argument unused during compilation: '-c' [-Wunused-command-line-argument]
error: C++26 was enabled in precompiled file 'CMakeFiles/__cmake_cxx23.dir/std.pcm' but is currently disabled
error: module file CMakeFiles/__cmake_cxx23.dir/std.pcm cannot be loaded due to a configuration mismatch with the current compilation [-Wmodule-file-config-mismatch]
/Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev/stagedir/lib/cmake/my_package/modules/algo-interface.cppm:17:17: error: use of undeclared identifier 'std'
17 | explicit Algo(std::string name)
| ^
/Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev/stagedir/lib/cmake/my_package/modules/algo-interface.cppm:24:3: error: use of undeclared identifier 'std'
24 | std::string m_name;
| ^
/Users/clausklein/Workspace/cpp/cxx20/cmake-init-modules/build/dev/stagedir/lib/cmake/my_package/modules/algo-interface.cppm:18:16: error: use of undeclared identifier 'std'
18 | : m_name(std::move(name))
| ^
5 errors generated.
[15/17] Linking CXX static library lib__cmake_cxx26.a
ninja: build stopped: subcommand failed.
67% tests passed, 1 tests failed out of 3
Total Test time (real) = 3.11 sec
The following tests FAILED:
3 - find-package-test (Failed)
Errors while running CTest
make: *** [all] Error 8
bash-5.3$