FindCUDAToolkit: Robust version checks when CUDA lang is not enabled

Previously if you set `CMAKE_CUDA_COMPILER` but hadn't enabled
the CUDA language, FindCUDAToolkit would not correctly compute
the version information.

Modules/FindCUDAToolkit.cmake

@@ -738,6 +738,7 @@ elseif(NOT CUDAToolkit_FIND_QUIETLY)
 endif()
 
 if(CUDAToolkit_NVCC_EXECUTABLE AND
+   CMAKE_CUDA_COMPILER_VERSION AND
    CUDAToolkit_NVCC_EXECUTABLE STREQUAL CMAKE_CUDA_COMPILER)
   # Need to set these based off the already computed CMAKE_CUDA_COMPILER_VERSION value
   # This if statement will always match, but is used to provide variables for MATCH 1,2,3...

Tests/Cuda/Toolkit/CMakeLists.txt

@@ -5,6 +5,10 @@ project(Toolkit CXX)
 # Validate that we can use CUDAToolkit to find cuda include paths
 find_package(CUDAToolkit REQUIRED)
 
+if(NOT DEFINED CUDAToolkit_VERSION)
+  message(FATAL_ERROR "expected CUDAToolkit variable CUDAToolkit_VERSION not found")
+endif()
+
 message(STATUS "CUDAToolkit_VERSION: ${CUDAToolkit_VERSION}")
 message(STATUS "CUDAToolkit_VERSION_MAJOR: ${CUDAToolkit_VERSION_MAJOR}")
 message(STATUS "CUDAToolkit_VERSION_MINOR: ${CUDAToolkit_VERSION_MINOR}")

Tests/CudaOnly/CMakeLists.txt

@@ -11,6 +11,7 @@ add_cuda_test_macro(CudaOnly.ExportPTX CudaOnlyExportPTX)
 add_cuda_test_macro(CudaOnly.SharedRuntimePlusToolkit CudaOnlySharedRuntimePlusToolkit)
 add_cuda_test_macro(CudaOnly.Standard98 CudaOnlyStandard98)
 add_cuda_test_macro(CudaOnly.Toolkit CudaOnlyToolkit)
+add_cuda_test_macro(CudaOnly.ToolkitBeforeLang CudaOnlyToolkitBeforeLang)
 add_cuda_test_macro(CudaOnly.WithDefs CudaOnlyWithDefs)
 add_cuda_test_macro(CudaOnly.CircularLinkLine CudaOnlyCircularLinkLine)
 add_cuda_test_macro(CudaOnly.ResolveDeviceSymbols CudaOnlyResolveDeviceSymbols)

Tests/CudaOnly/Toolkit/CMakeLists.txt

@@ -2,6 +2,10 @@ cmake_minimum_required(VERSION 3.15)
 project(CudaOnlyToolkit CUDA)
 find_package(CUDAToolkit REQUIRED)
 
+if(NOT DEFINED CUDAToolkit_VERSION)
+  message(FATAL_ERROR "expected CUDAToolkit variable CUDAToolkit_VERSION not found")
+endif()
+
 message(STATUS "CUDAToolkit_VERSION: ${CUDAToolkit_VERSION}")
 message(STATUS "CUDAToolkit_VERSION_MAJOR: ${CUDAToolkit_VERSION_MAJOR}")
 message(STATUS "CUDAToolkit_VERSION_MINOR: ${CUDAToolkit_VERSION_MINOR}")

Tests/CudaOnly/ToolkitBeforeLang/CMakeLists.txt

@@ -0,0 +1,26 @@
+cmake_minimum_required(VERSION 3.15)
+project(CudaOnlyToolkitBeforeLang CXX)
+
+# Validate that CUDAToolkit gets the correct version
+# when called before CUDA the language is enabled
+find_package(CUDAToolkit REQUIRED)
+enable_language(CUDA)
+
+if(NOT DEFINED CUDAToolkit_VERSION)
+  message(FATAL_ERROR "expected CUDAToolkit variable CUDAToolkit_VERSION not found")
+endif()
+
+set(cuda_libs cudart cuda_driver)
+
+# Verify that all the CUDA:: targets and variables exist
+foreach (cuda_lib IN LISTS cuda_libs)
+  if(NOT CUDA_${cuda_lib}_LIBRARY)
+    message(FATAL_ERROR "expected CUDAToolkit variable CUDA_${cuda_lib}_LIBRARY not found")
+  endif()
+  if(NOT TARGET CUDA::${cuda_lib})
+    message(FATAL_ERROR "expected CUDAToolkit target CUDA::${cuda_lib} not found")
+  endif()
+endforeach()
+
+add_executable(CudaOnlyToolkitBeforeLang main.cu)
+target_link_libraries(CudaOnlyToolkitBeforeLang PRIVATE CUDA::toolkit)

Tests/CudaOnly/ToolkitBeforeLang/main.cu

@@ -0,0 +1,8 @@
+// Only thing we care about is that these headers are found
+#include <cuda.h>
+#include <cuda_runtime_api.h>
+
+int main(int argc, char** argv)
+{
+  return 0;
+}