How to specify gcm.cache location using g++ & CMake - c++

Question

I am currently working on a project which requires C++20 (g++ v11) features and CMake. The project tree is similar to the following one:
- Top level
- src
- IO
- IO.cpp
- CMakeLists.txt
- main.cpp
- CMakeLists.txt
CMake compiles IO module without any problem but It generates gcm.cache folder in a following way:
- build
- Some other CMake files and folders
- bin
- lib
- src
- IO
- gcm.cache
- IO.gcm
Therefore, g++ can not find gcm.cache folder and gives me this error:
IO: error: failed to read compiled module: No such file or directory
IO: note: compiled module file is 'gcm.cache/IO.gcm'
IO: note: imports must be built before being imported
IO: fatal error: returning to the gate for a mechanical issue
I would be grateful if anyone tell me that there is a way to specify gcm.cache locations using CMake or force CMake to search gcm files recursively or tell it to create a top level gcm.cache and store everything inside of it. I can not find any answer on anywhere since C++20 documentations are terrible. Thanks in advance...

Answer 1

I have experienced the exact same issue, and without actually discovering a solution have found a workaround. Complete code found here.
In short, I create a symbolic link such that subprojects are all using the gcm.cache/ directory located in the root directory of the project. Create a symlink like so:
ln -fs ../gcm.cache gcm.cache
This is the directory tree of the project:
.
├── engine
│   ├── core
│   │   └── types.cpp
│   ├── engine.cpp
│   ├── gcm.cache -> ../gcm.cache
│   ├── Makefile
│   └── memory
├── gcm.cache
├── init.sh
├── Makefile
└── testgame
├── gamelib.cpp
├── gcm.cache -> ../gcm.cache
├── Makefile
└── test.cpp
So when gcc builds the engine and testgame projects it actually uses the gcm.cache/ from the root directory. Until something better comes along this is my go-to method.