opencv: misc cleanups; fix CUDA build (#339619)

pkgs/development/cuda-modules/tests/opencv-and-torch/default.nix

@@ -0,0 +1,81 @@
+{
+  cudaPackages,
+  lib,
+  writeGpuTestPython,
+  # Configuration flags
+  openCVFirst,
+  useOpenCVDefaultCuda,
+  useTorchDefaultCuda,
+}:
+let
+  inherit (lib.strings) optionalString;
+
+  openCVBlock = ''
+
+    import cv2
+    print("OpenCV version:", cv2.__version__)
+
+    # Ensure OpenCV can access the GPU.
+    assert cv2.cuda.getCudaEnabledDeviceCount() > 0, "No CUDA devices found for OpenCV"
+    print("OpenCV CUDA device:", cv2.cuda.printCudaDeviceInfo(cv2.cuda.getDevice()))
+
+    # Ensure OpenCV can access the GPU.
+    print(cv2.getBuildInformation())
+
+    a = cv2.cuda.GpuMat(size=(256, 256), type=cv2.CV_32S, s=1)
+    b = cv2.cuda.GpuMat(size=(256, 256), type=cv2.CV_32S, s=1)
+    c = int(cv2.cuda.sum(cv2.cuda.add(a, b))[0]) # OpenCV returns a Scalar float object.
+
+    assert c == 2 * 256 * 256, f"Expected {2 * 256 * 256} OpenCV, got {c}"
+
+  '';
+
+  torchBlock = ''
+
+    import torch
+    print("Torch version:", torch.__version__)
+
+    # Set up the GPU.
+    torch.cuda.init()
+    # Ensure the GPU is available.
+    assert torch.cuda.is_available(), "CUDA is not available to Torch"
+    print("Torch CUDA device:", torch.cuda.get_device_properties(torch.cuda.current_device()))
+
+    a = torch.ones(256, 256, dtype=torch.int32).cuda()
+    b = torch.ones(256, 256, dtype=torch.int32).cuda()
+    c = (a + b).sum().item()
+    assert c == 2 * 256 * 256, f"Expected {2 * 256 * 256} for Torch, got {c}"
+
+  '';
+
+  content = if openCVFirst then openCVBlock + torchBlock else torchBlock + openCVBlock;
+
+  torchName = "torch" + optionalString useTorchDefaultCuda "-with-default-cuda";
+  openCVName = "opencv4" + optionalString useOpenCVDefaultCuda "-with-default-cuda";
+in
+# TODO: Ensure the expected CUDA libraries are loaded.
+# TODO: Ensure GPU access works as expected.
+writeGpuTestPython {
+  name = if openCVFirst then "${openCVName}-then-${torchName}" else "${torchName}-then-${openCVName}";
+  libraries =
+    # NOTE: These are purposefully in this order.
+    pythonPackages:
+    let
+      effectiveOpenCV = pythonPackages.opencv4.override (prevAttrs: {
+        cudaPackages = if useOpenCVDefaultCuda then prevAttrs.cudaPackages else cudaPackages;
+      });
+      effectiveTorch = pythonPackages.torchWithCuda.override (prevAttrs: {
+        cudaPackages = if useTorchDefaultCuda then prevAttrs.cudaPackages else cudaPackages;
+      });
+    in
+    if openCVFirst then
+      [
+        effectiveOpenCV
+        effectiveTorch
+      ]
+    else
+      [
+        effectiveTorch
+        effectiveOpenCV
+      ];
+} content