Issue with std::filesystem and GCC 8 about adaptivecpp HOT 2 OPEN

Can you elaborate why/how stdc++fs is not linked properly? We do have a lengthy cmake module that is supposed to take care of all the different filesystem variants, and should also handle stdc++fs. If special casing is needed, it would be preferable to happen there:
https://github.com/AdaptiveCpp/AdaptiveCpp/blob/develop/cmake/FindFilesystem.cmake

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Apologies, I hadn't seen that module - it's good and will build the shared object correctly. The problem probably only arises in this special case - GCC 9 system compiler (i.e. C++17's std::filesystem symbols in libstdc++.so.6) and using GCC 8 to compile. I can only assume that the linker discards seemingly unused symbols when linking in libstdc++fs.a, which then again get loaded at runtime from libstdc++.so.6. This potential problem can be avoided by linking libstdc++fs.a in its entirety, which since the archive is small doesn't lead to much bloat.

Line 270 of FindFilesystem.cmake then becomes:
set_property(TARGET std::filesystem APPEND PROPERTY INTERFACE_LINK_LIBRARIES -Wl,--whole-archive stdc++fs -Wl,--no-whole-archive)

from adaptivecpp.