libtorch-bin: fix passthru.tests for CUDA

- Provide the CUDA toolkit and CuDNN dependencies.
- Expose libcuda.so stub to run the test in the sandbox.

pkgs/development/libraries/science/math/libtorch/test/default.nix

@@ -1,6 +1,28 @@
-{ stdenv, cmake, libtorch-bin, symlinkJoin }:
+{ lib
+, stdenv
+, cmake
+, libtorch-bin
+, linkFarm
+, symlinkJoin
 
-stdenv.mkDerivation {
+, cudaSupport
+, cudatoolkit
+, cudnn
+}:
+let
+  cudatoolkit_joined = symlinkJoin {
+    name = "${cudatoolkit.name}-unsplit";
+    paths = [ cudatoolkit.out cudatoolkit.lib ];
+  };
+
+  # We do not have access to /run/opengl-driver/lib in the sandbox,
+  # so use a stub instead.
+  cudaStub = linkFarm "cuda-stub" [{
+    name = "libcuda.so.1";
+    path = "${cudatoolkit}/lib/stubs/libcuda.so";
+  }];
+
+in stdenv.mkDerivation {
   pname = "libtorch-test";
   version = libtorch-bin.version;
 
@@ -8,7 +30,11 @@ stdenv.mkDerivation {
 
   nativeBuildInputs = [ cmake ];
 
-  buildInputs = [ libtorch-bin ];
+  buildInputs = [ libtorch-bin ] ++
+    lib.optionals cudaSupport [ cudnn ];
+
+  cmakeFlags = lib.optionals cudaSupport
+    [ "-DCUDA_TOOLKIT_ROOT_DIR=${cudatoolkit_joined}" ];
 
   doCheck = true;
 
@@ -17,6 +43,7 @@ stdenv.mkDerivation {
   '';
 
   checkPhase = ''
-    ./test
+    LD_LIBRARY_PATH=${cudaStub}''${LD_LIBRARY_PATH:+:}$LD_LIBRARY_PATH \
+      ./test
   '';
 }