// build.rs for rtx-transformers
//
// When the "cuda" feature is active this build script compiles the
// `rope_forward.cu` kernel using NVRTC at *runtime* (via `cudarc`), so there
// is no hard build-time dependency on nvcc.  The build script only instructs
// Cargo to re-run when the kernel source changes.
//
// If CUDA is not enabled (the default) this build script is a no-op.

fn main() {
    // Only relevant when the cuda feature is active.
    #[cfg(feature = "cuda")]
    cuda_setup();

    // Always tell Cargo to re-run if *this* script changes.
    println!("cargo:rerun-if-changed=build.rs");
}

#[cfg(feature = "cuda")]
fn cuda_setup() {
    // Track the kernel source so Cargo rebuilds when it changes.
    println!("cargo:rerun-if-changed=src/cuda_kernels/rope_forward.cu");

    // Emit the cuda feature flag for conditional compilation inside the crate.
    println!("cargo:rustc-cfg=feature=\"cuda\"");
}