Use C++20 modules

[ken-matsui]

TODO for this issue

• Migrate sources to modules: Migrate sources to C++20 modules #776
• Migrate tests to modules: Migrate tests to modules #787
• Fix CIs somehow
• (opt) figure out how to publish to Homebrew

Roadmap

1. Use modules internally
2. Support git dependencies
3. Support building modules, i.e. build Poac itself

Build Steps

Currently cannot build tests.

export CXX=/opt/homebrew/opt/llvm/bin/clang++
cmake -B build -G Ninja -DPOAC_BUILD_TESTING=OFF
cd build
ninja

Current Status

On macOS, Poac can be built except for tests.

https://github.com/poac-dev/poac/actions/runs/5042517134

Known Issues

$ ./poac create hello 
poac(89900,0x1f1121e00) malloc: nano zone abandoned due to inability to reserve vm space.
[2023-05-21 23:21:47.791] [info]      Created binary (application) `hello` package

1. Weird message from malloc => Use MallocNanoZone, like MallocNanoZone=0 ./poac create hello (cf. https://stackoverflow.com/questions/64126942/malloc-nano-zone-abandoned-due-to-inability-to-preallocate-reserved-vm-space)
2. spdlog::set_pattern("%v") in src/main.cc isn't working

Opaque pointers are only supported in -opaque-pointers mode might be related.

Compilers

• Clang 16 (Apple Clang doesn't work)

[ken-matsui]

Stop using C++20 modules, will use a different way to structure the project when I have time next.