Dynamic loading of libraries broken on NixOS

[ehmry]

Nim binaries run on NixOS give an error when loading libraries that look similar to this:
could not load: libcrypto.so(.1.1|.1.0.2|.1.0.1|.1.0.0|.0.9.9|.0.9.8|.47|.46|.45|.44|.43|.41|.39|.38|.10|).

This is because NixOS does not have a system-wide directory that libraries can be loaded from by name (libcrypto.so). Normally a binary while have a RUNPATH/rpath set in the ELF header that contains absolute paths to packages in the Nix store where the loader will look for libraries, for example: /nix/store/…-glibc-2.31/lib:/nix/store/…-gcc-9.3.0-lib/lib. During the Nix build process for packages these paths are added by detecting and passing the necessary -rpath flags to the linker.

This problem can be fixed by amending the binary RUNPATH after compilation using the patchelf tool, but I cannot think of any easy way to detect which libraries the binary might load at runtime, nor how to perform the patch automatically outside of building NIx packages.

I propose to adjust the Nim compiler to load libraries on NixOS by absolute path rather than simple names, and to detect the absolute at compile time. This would fix the loading problem and improve performance by avoiding the heuristic library search at runtime. This behavior could be controlled by an additional option for the Nim compiler, and the compiler take its search paths from environmental variables that are present in Nix package builds and development environments.

[ehmry]

This can be fixed downstream.