test cuda: import fmt in CUDA source code

Current test is only for Windows(cl.exe).
Need to test more with the other host compilers...

* Activate the test when `find_package(CUDA)` worked
* The test runs with C++14

Detailed comments in 'test/cuda-test'

test/CMakeLists.txt

@@ -225,3 +225,22 @@ if (FMT_PEDANTIC AND NOT WIN32)
     "-DPEDANTIC_COMPILE_FLAGS=${PEDANTIC_COMPILE_FLAGS}"
     "-DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}")
 endif ()
+
+#
+# Activate CUDA related tests (Optional)
+# if and only if we can find the CUDA in current CMake run.
+#
+find_package(CUDA 9.2)
+if(CUDA_FOUND)
+  add_test(cuda-test ${CMAKE_CTEST_COMMAND}
+    -C ${CMAKE_BUILD_TYPE}
+    --build-and-test
+    "${CMAKE_CURRENT_SOURCE_DIR}/cuda-test"
+    "${CMAKE_CURRENT_BINARY_DIR}/cuda-test"
+    --build-generator ${CMAKE_GENERATOR}
+    --build-makeprogram ${CMAKE_MAKE_PROGRAM}
+    --build-options
+      "-DFMT_DIR=${PROJECT_BINARY_DIR}"
+      "-DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}"
+  )
+endif()

test/cuda-test/CMakeLists.txt

@@ -0,0 +1,104 @@
+
+#
+# We can find some usecases which follows the guide of CMake.
+# The way replaces 'find_package(CUDA)' to 'enable_language(CUDA)'.
+# And let the CMake built-in functions to use NVCC.
+#
+# See: https://cmake.org/cmake/help/latest/module/FindCUDA.html#replacement
+#
+# However, such CMake versions are pretty high (3.10 or later).
+# And we can't sure most of the CUDA projects are using those latest
+# because the latest C++ standard for NVCC is C++ 14 at this moment.
+#
+# In conclusion, this test will use older version of CMake,
+# and rely on 'find_package(CUDA)'. For its version, do follow the Root CMakeLists.txt.
+#
+
+#
+# cmake_minimum_required(VERSION 3.10)
+# project(fmt-cuda-test LANGUAGES CXX CUDA) # see 'enable_language(CUDA)'
+cmake_minimum_required(VERSION 3.1) # for C++ 14
+project(fmt-cuda-test LANGUAGES CXX)
+
+# find from ${PROJECT_BINARY_DIR}
+find_package(FMT    REQUIRED) 
+
+# The environment variables(CUDA_BIN_PATH & CUDA_PATH) must be specified at this point
+find_package(CUDA   REQUIRED)
+
+#
+# Update these when NVCC becomes ready for C++ 17 features
+# https://docs.nvidia.com/cuda/cuda-c-programming-guide/index.html#cpp14-language-features
+#
+set(CMAKE_CUDA_STANDARD 14)
+set(CMAKE_CUDA_STANDARD_REQUIRED 14)
+
+list(APPEND CUDA_NVCC_FLAGS "-std=c++14")
+if(MSVC)
+    # this is the solution of pytorch
+    #   https://github.com/pytorch/pytorch/pull/7118
+    list(APPEND CUDA_NVCC_FLAGS "-Xcompiler" "/std:c++14")
+    list(APPEND CUDA_NVCC_FLAGS "-Xcompiler" "/Zc:__cplusplus")
+    # for the reason of this -Xcompiler options, see below ...
+endif()
+
+#
+# In this test, we will assume that 
+# the user is going to pre-compile CUDA source codes
+# with some libraries (including this 'fmt').
+#
+# In addition to that, 
+# this test will invoke both C++ Host compiler and NVCC 
+# by providing another (non-CUDA) C++ source code
+#
+cuda_add_executable(fmt-in-cuda-test
+    cuda-cpp14.cu
+    cpp14.cc
+)
+
+#
+# https://docs.nvidia.com/cuda/cuda-compiler-driver-nvcc/index.html
+#
+set_target_properties(fmt-in-cuda-test
+PROPERTIES
+    CXX_STANDARD 14 # Notice this is for C++ code
+    POSITION_INDEPENDENT_CODE ON
+)
+# target_compile_features(fmt-in-cuda-test
+# PRIVATE
+#     cxx_std_14 # just make sure of the property is available
+# )
+
+get_target_property(cuda_standard 
+    fmt-in-cuda-test CUDA_STANDARD
+)
+message(STATUS "cuda_standard:          ${cuda_standard}")
+
+get_target_property(cuda_standard_required
+    fmt-in-cuda-test CUDA_STANDARD_REQUIRED
+)
+message(STATUS "cuda_standard_required: ${cuda_standard_required}")
+
+#
+# https://cmake.org/cmake/help/latest/module/FindCUDA.html
+#
+# From the document, you can see "The default is to use no keyword"
+#
+target_link_libraries(fmt-in-cuda-test
+# PUBLIC
+    fmt::fmt
+)
+
+if(MSVC)
+    #
+    # MSVC places incorrect '__cplusplus' macro. Follow the guideline.
+    #
+    # https://github.com/Microsoft/vscode-cpptools/issues/2595
+    # https://devblogs.microsoft.com/cppblog/msvc-now-correctly-reports-__cplusplus/
+    #
+    target_compile_options(fmt-in-cuda-test
+    PRIVATE
+        /Zc:__cplusplus
+        /permissive-
+    )
+endif()

test/cuda-test/cpp14.cc

@@ -0,0 +1,8 @@
+
+#include <fmt/core.h>
+
+static_assert(__cplusplus >= 201402L, "expect C++ 2014");
+
+auto make_message_cpp() -> std::string{
+    return fmt::format("host compiler\t: __cplusplus == {}", __cplusplus);
+}

test/cuda-test/cuda-cpp14.cu

@@ -0,0 +1,32 @@
+
+//
+//  nvcc -x cu -std=c++14 ..\test\cuda-test\include_test.cu -I"../include" -Xcompiler /Zc:__cplusplus  -l"fmtd" -L"../build/Debug"
+//
+
+//
+// Ensure that we are using the expected standard
+// https://en.cppreference.com/w/cpp/preprocessor/replace#Predefined_macros
+//
+static_assert(__cplusplus >= 201402L, "expect C++ 2014 for nvcc");
+
+#if defined(__CUDACC__)
+#   define FMT_DEPRECATED
+#endif
+#include <fmt/core.h>
+
+#include <cuda.h>
+#include <iostream>
+
+using namespace std;
+
+extern auto make_message_cpp() -> std::string;
+extern auto make_message_cuda() -> std::string;
+
+int main(int, char*[]){
+    cout << make_message_cuda() << endl;
+    cout << make_message_cpp() << endl;
+}
+
+auto make_message_cuda() -> std::string{
+    return fmt::format("nvcc         \t: __cplusplus == {}", __cplusplus);
+}