Modules crash and/or linker failure

[mmoult]

I encountered an issue which I believe to be a bug in clang. The compilation fails during linking, and with some minor modifications to the code, clang crashes. Unfortunately, when I was coming up with the reduced version, I maintained the linker failure but lost the clang crash. Hopefully an investigation into the problem which I kept can fix both. If you can verify that this is a bug (and not a programming mistake on my part), I will take the time to produce the crash report.

I have attached all relevant code files: files.zip The issue appears to be coming from the vector parameter of Foo::noo (in previous tests, I observed that when the parameter is replaced with a bool or a vector of some other type, the error goes away. Interesting that Bar* is permitted as a return, but not as a specialization of vector.)

The error I am getting looks like this:

[10/10] Linking CXX executable modules-test
FAILED: modules-test 
: && /home/mmoult/Build/llvm-project-llvmorg-18.1.1/build/bin/clang++ -g  CMakeFiles/build.dir/main.cpp.o CMakeFiles/build.dir/foo.cpp.o CMakeFiles/build.dir/bar.cxx.o CMakeFiles/build.dir/foo.cxx.o -o modules-test   && :
/usr/bin/ld: CMakeFiles/build.dir/foo.cpp.o: in function `Foo@foo::doo()':
/home/mmoult/git/test/foo.cpp:10: undefined reference to `Foo@foo::num'
/usr/bin/ld: CMakeFiles/build.dir/bar.cxx.o: in function `Bar@bar::call() const':
/home/mmoult/git/test/bar.cxx:12: undefined reference to `Foo@foo::num'
clang++: error: linker command failed with exit code 1 (use -v to see invocation)
ninja: build stopped: subcommand failed.

The command I ran on Debian is:

cmake -G Ninja -B build -S . -DCMAKE_BUILD_TYPE=Debug

The version of CMake I am using is 3.29.0-rc4, found at https://cmake.org/download/ (version 3.29.0-rc3 produced the same error).
The version of Ninja I am using is 1.11.1
The version of clang I am using is:

clang version 18.1.1
Target: x86_64-unknown-linux-gnu
Thread model: posix
InstalledDir: /home/mmoult/Build/llvm-project-llvmorg-18.1.1/build/bin

Thanks for your consideration.