How to use the cppm module in a CMake project?

[ichlubna]

I use the standard inclusion as:

find_package(glm REQUIRED)
...
target_link_libraries(${PROJECT_NAME}  glm)

But when I use import glm; I get:
fatal error: unknown compiled module interface: no such module

I cannot find instructions about the usage of the module version of glm anywhere, although people seem to be already using it, for example at #1298 or #1260. I'd appreciate any guidance. Thanks!

[jsoulier]

Just to add, also has been asked here: #1208
It's not very clear what the intended usage is

[ichlubna]

Thanks for the link @jsoulier. Seems like it was an attempt that died with no further support.

[adam4813]

A work around, that will require a tweak based on you setup, that I found here and adapted to my situation

# Hack to convert glm to a C++20 module target
add_library(glm-module)
target_sources(glm-module PUBLIC
        FILE_SET CXX_MODULES
        FILES ${glm_DIR}/../../include/glm/glm.cppm # glm_DIR is where the glmConfig.cmake is located **ADJUST BASED ON YOUR SETUP**
)
target_link_libraries(glm-module PUBLIC glm::glm)

And then for my add_[library|program] target

target_link_libraries(target-name
    PRIVATE
        #glm::glm # the current way
        glm-module # Use the C++20 module version of GLM created in Dependencies.cmake
)

This creates a new library module within your ecosystem, that containerizes glm into a c++ module.

I did run into an issue with wasm not playing nice, but this could be my setup, so I used the following to make it work either way

#ifdef EMSCRIPTEN
#include <glm/glm.hpp>
#else
import glm; // Ensure glm is available in the module context
#endif

[ichlubna]

Thanks for sharing this @adam4813

[adam4813]

This is not battle tested, so YMMV

A small tweak I just made to make intellisense happier was linking glm::glm to the pseudo-module target via PUBLIC

target_link_libraries(glm-module PUBLIC glm::glm)

[adam4813]

After some further review, it turns out import glm; will work without the emscripten pre-processor to conditionally include the header instead. I just needed to remove a cmake configuration add_compile_options(-pthread)

Additionally, I was compiling clang with add_compile_options(-fmodules). Don't do this, you don't need to set a special flag at all. This SO thread led me to check the official clang docs https://stackoverflow.com/a/77169415