so it seems, your toolchain does not support import std or is wrong installed!
Do you find libc++.modules.json or libstdc++.modules.json in C:\dev\toolchains\llvm tree?
I do have libc++.modules.json in C:\dev\toolchains\llvm\lib\libc++.modules.json
please see No SOURCES given to target: __CMAKE__CXX26 on ubuntu 25.04 - #11 by ClausKlein
you may trace CMakeDetermineComilerId.cmake while configure oder compile the file yourself.
Nope, this is enough. We have gone full circle. It is the developers job to deal with this.
5 sec before the destination you give it up?
We need the output of:
/usr/local/Cellar/llvm/20.1.6/bin/clang++ -stdlib=libc++ -E -x c++-header /Users/clausklein/.local/share/cmake-4.0/Modules/CXX-DetectStdlib.h
or
CXX=clang++ CXXFLAGS=-stdlib=libc++ ~/.local/bin/cmake -G Ninja -S . -B build --fresh --trace-expand --trace-source=CMakeDetermineCompilerId.cmake
but use your right path to the your tools!
Here you go, CMake 4.0.3 and clang 21 compiled from source with bin folder on PATH.
I’m on Windows 10 and the Powershell is used in the log
log.txt (163.4 KB)
@ben.boeckel Is this a cmake or a toolchain problem?
CMAKE-STDLIB-DETECT: UNKNOWN