clang-rs does not search LIBRARY_PATH and instead picks libraries in /usr/lib/xxx

[molysgaard]

It seems that clang-rs does not search for libraries in the environment variable LIBRARY_PATH during execution of the build.rs script.

I am using GUIX (like NIX) and my library path is /gnu/store/qb41j953iam58gj3cwsz9jlnnfn25cwa-profile/lib.
In that folder there is a libclang and libLLVM etc.
But it seems that the build.rs script is instead linking with the libclang and libllvm that is present in /lib/x86_64-linux-gnu/.
This leads to all sorts of linker errors, see snippet below:

  = note: ld: /lib/x86_64-linux-gnu/libedit.so.2: undefined reference to `__isoc23_wcstol@GLIBC_2.38'
          ld: /lib/x86_64-linux-gnu/libLLVM-17.so.1: undefined reference to `arc4random@GLIBC_2.36'
          ld: /lib/x86_64-linux-gnu/libbsd.so.0: undefined reference to `__isoc23_strtoimax@GLIBC_2.38'
          ld: /lib/x86_64-linux-gnu/libLLVM-17.so.1: undefined reference to `__isoc23_strtoull@GLIBC_2.38'
          ld: /lib/x86_64-linux-gnu/libLLVM-17.so.1: undefined reference to `__isoc23_sscanf@GLIBC_2.38'
          ld: /usr/lib/llvm-17/lib/libclang-17.0.6.so: undefined reference to `__isoc23_strtoul@GLIBC_2.38'
          ld: /lib/x86_64-linux-gnu/libLLVM-17.so.1: undefined reference to `std::condition_variable::wait(std::unique_lock<std::mutex>&)@GLIBCXX_3.4.30'
          ld: /lib/x86_64-linux-gnu/libLLVM-17.so.1: undefined reference to `fmodf@GLIBC_2.38'
          ld: /usr/lib/llvm-17/lib/libclang-17.0.6.so: undefined reference to `__isoc23_strtol@GLIBC_2.38'
          ld: /lib/x86_64-linux-gnu/libLLVM-17.so.1: undefined reference to `fmod@GLIBC_2.38'
          ld: /lib/x86_64-linux-gnu/libLLVM-17.so.1: undefined reference to `__isoc23_scanf@GLIBC_2.38'
          ld: /lib/x86_64-linux-gnu/libbsd.so.0: undefined reference to `__isoc23_strtoumax@GLIBC_2.38'
          ld: /lib/x86_64-linux-gnu/libLLVM-17.so.1: undefined reference to `__isoc23_strtoll@GLIBC_2.38'

Why fix this?

The LIBRARY_PATH variable is a convention established by gcc, and it makes sense to follow it.
See here https://gcc.gnu.org/onlinedocs/gcc/Environment-Variables.html#index-LIBRARY_005fPATH

How to fix this:

If LIBRARY_PATH is set, the build.rs script should search for libclang and similar in all the paths specified there, before it looks anywhere else. This is compatible with how gcc works.