Unable do Compile Rust-CUDA because missing CUDNN includes.

Hello everyone,

I am trying to compile Rust-Cuda on Ubuntu 24.04 with Cuda Toolkit 12.8 and driver 550.120. Cargo version is cargo 1.86.0 (adf9b6ad1 2025-02-28). I have just cloned the repository from the main branch.

First, I had problems regarding the Optix SDK. cargo build returned that it could not find the SDK. After digging a bit, I found this line on the optix-sys crate:

const OPTIX_ROOT_ENVS: &[&str] = &["OPTIX_ROOT", "OPTIX_ROOT_DIR"];

So I set OPTIX_ROOT to directory where I placed the SDK, and it worked. But now I got another problem:

error: failed to run custom build command for `cudnn-sys v0.1.0 (/home/npbrust/Rust-CUDA/crates/cudnn-sys)`

Caused by:
  process didn't exit successfully: `/home/npbrust/Rust-CUDA/target/debug/build/cudnn-sys-640a99c44abeadd2/build-script-main` (exit status: 101)
  --- stderr

  thread 'main' panicked at crates/cudnn-sys/build/main.rs:7:42:
  Cannot create cuDNN SDK instance.: "Cannot find cuDNN include directory."
  note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

So I download the cuDNN (cudnn-linux-x86_64-9.8.0.87_cuda12-archive). After expanding the file, I copied the contents of the include and lib directories into /usr/local/cuda/include and /usr/local/cuda/lib64. cargo build gave me the same error. Then I tried setting the variables CUDNN_INCLUDE_DIR and CUDNN_LIBRARY to the include and lib directories, but that got me nowhere. The question is: how should I point cargo do find the CUDNN includes? Looking at the code for the cudnn_sys crate gave me no directions.

Best Regards.

Start with crates/cudnn-sys/build/main.rs and reproduce the failure using the reported Ubuntu, CUDA, cuDNN, and cargo versions. Trace how the build script discovers the cuDNN include directory; done means the repository builds with a documented, working include-path configuration.