py-torch-nvidia-apex: fix +cuda build (#33070)

var/spack/repos/builtin/packages/py-torch-nvidia-apex/1499.patch

@@ -0,0 +1,13 @@
+diff --git a/setup.py b/setup.py
+index 063b42d..7388297 100644
+--- a/setup.py
++++ b/setup.py
+@@ -31,7 +31,7 @@ if not torch.cuda.is_available():
+           'and, if the CUDA version is >= 11.0, Ampere (compute capability 8.0).\n'
+           'If you wish to cross-compile for a single specific architecture,\n'
+           'export TORCH_CUDA_ARCH_LIST="compute capability" before running setup.py.\n')
+-    if os.environ.get("TORCH_CUDA_ARCH_LIST", None) is None:
++    if os.environ.get("TORCH_CUDA_ARCH_LIST", None) is None and cpp_extension.CUDA_HOME is not None:
+         _, bare_metal_major, _ = get_cuda_bare_metal_version(cpp_extension.CUDA_HOME)
+         if int(bare_metal_major) == 11:
+             os.environ["TORCH_CUDA_ARCH_LIST"] = "6.0;6.1;6.2;7.0;7.5;8.0"

var/spack/repos/builtin/packages/py-torch-nvidia-apex/package.py

@@ -26,7 +26,8 @@ class PyTorchNvidiaApex(PythonPackage, CudaPackage):
     variant("cuda", default=True, description="Build with CUDA")
 
     # https://github.com/NVIDIA/apex/issues/1498
-    conflicts("~cuda")
+    # https://github.com/NVIDIA/apex/pull/1499
+    patch("1499.patch", when="@2020-10-19")
 
     def setup_build_environment(self, env):
         if "+cuda" in self.spec:
@@ -37,6 +38,8 @@ def setup_build_environment(self, env):
                     for i in self.spec.variants["cuda_arch"].value
                 )
                 env.set("TORCH_CUDA_ARCH_LIST", torch_cuda_arch)
+        else:
+            env.unset("CUDA_HOME")
 
     def global_options(self, spec, prefix):
         args = []