feat: Use cpp20 by default (#2839)

Author: sbstndb

CMakeLists.txt

@@ -194,7 +194,7 @@ target_include_directories(xtensor INTERFACE
     $<BUILD_INTERFACE:${XTENSOR_INCLUDE_DIR}>
     $<INSTALL_INTERFACE:include>)
 
-target_compile_features(xtensor INTERFACE cxx_std_17)
+target_compile_features(xtensor INTERFACE cxx_std_20)
 
 target_link_libraries(xtensor INTERFACE xtl)
 
@@ -205,7 +205,7 @@ OPTION(BUILD_TESTS "xtensor test suite" OFF)
 OPTION(BUILD_BENCHMARK "xtensor benchmark" OFF)
 OPTION(DOWNLOAD_GBENCHMARK "download google benchmark and build from source" ON)
 OPTION(DEFAULT_COLUMN_MAJOR "set default layout to column major" OFF)
-OPTION(CPP20 "enables C++20 (experimental)" OFF)
+OPTION(CPP23 "enables C++23 (experimental)" OFF)
 OPTION(XTENSOR_DISABLE_EXCEPTIONS "Disable C++ exceptions" OFF)
 OPTION(DISABLE_MSVC_ITERATOR_CHECK "Disable the MVSC iterator check" ON)
 

test/CMakeLists.txt

@@ -34,27 +34,27 @@ string(TOUPPER "${CMAKE_BUILD_TYPE}" U_CMAKE_BUILD_TYPE)
 
 include(set_compiler_flag.cmake)
 
-if(CPP20)
-  # User requested C++17, but compiler might not oblige.
+if(CPP23)
+  # User requested C++23, but compiler might not oblige.
   set_compiler_flag(
     _cxx_std_flag CXX
-    "-std=c++2a"  # this should work with GNU, Intel, PGI
-    "/std:c++20"  # this should work with MSVC
+    "-std=c++23"  # this should work with GNU, Intel, PGI
+    "/std:c++23"  # this should work with MSVC
   )
   if(_cxx_std_flag)
-    message(STATUS "Building with C++20")
+    message(STATUS "Building with C++23")
   endif()
 else()
   set_compiler_flag(
     _cxx_std_flag CXX REQUIRED
-    "-std=c++17"  # this should work with GNU, Intel, PGI
-    "/std:c++17"  # this should work with MSVC
+    "-std=c++20"  # this should work with GNU, Intel, PGI
+    "/std:c++20"  # this should work with MSVC
   )
-  message(STATUS "Building with C++17")
+  message(STATUS "Building with C++20")
 endif()
 
 if(NOT _cxx_std_flag)
-  message(FATAL_ERROR "xtensor needs a C++17-compliant compiler.")
+  message(FATAL_ERROR "xtensor needs a C++20-compliant compiler.")
 endif()
 
 OPTION(XTENSOR_ENABLE_WERROR "Turn on -Werror" OFF)
@@ -74,7 +74,7 @@ if(CMAKE_CXX_COMPILER_ID MATCHES "GNU" OR (CMAKE_CXX_COMPILER_ID MATCHES "Intel"
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Werror -DSKIP_ON_WERROR")
   endif()
 elseif(CMAKE_CXX_COMPILER_ID MATCHES "MSVC")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${_cxx_std_flag} /MP /bigobj")
+  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${_cxx_std_flag} /Zc:__cplusplus /MP /bigobj")
   set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} /MANIFEST:NO")
   add_definitions(-D_CRT_SECURE_NO_WARNINGS)
   add_definitions(-D_SILENCE_TR1_NAMESPACE_DEPRECATION_WARNING)

test/test_xbuilder.cpp

@@ -676,7 +676,13 @@ namespace xt
 
         xt::dynamic_shape<std::size_t> sd = {3, 2, 1};
         auto ed1 = empty<double>(sd);
-        auto ed2 = empty<double, layout_type::column_major>(dynamic_shape<std::size_t>({3, 3, 3}));
+// TODO : The ed2 expression do not work on MSVC due to bad deduction since cpp20. We need to fix it for MSVC.
+#if defined(_MSVC_LANG)
+        using ShapeType = xt::dynamic_shape<std::size_t>;
+        auto ed2 = empty<double, xt::layout_type::column_major, ShapeType>(ShapeType({3, 3, 3}));
+#else
+        auto ed2 = empty<double, xt::layout_type::column_major>(xt::dynamic_shape<std::size_t>({3, 3, 3}));
+#endif
         auto ed3 = empty<double>(std::vector<std::size_t>({3, 3, 3}));
         b = std::is_same<decltype(ed1), xarray<double>>::value;
         EXPECT_TRUE(b);