feat(CMake): enable optional C++20 support (#7075)

conf/dist/config.cmake

@@ -84,3 +84,6 @@ endif()
 # Source tree in IDE
 set(WITH_SOURCE_TREE       "hierarchical" CACHE STRING "Build the source tree for IDE's.")
 set_property(CACHE WITH_SOURCE_TREE PROPERTY STRINGS no flat hierarchical)
+
+# If disable - use c++17
+option(USE_CPP_20 "Enable c++20 standard" 0)

src/cmake/macros/ConfigureBaseTargets.cmake

@@ -9,28 +9,15 @@ add_library(acore-compile-option-interface INTERFACE)
 # Use -std=c++11 instead of -std=gnu++11
 set(CXX_EXTENSIONS OFF)
 
-# Enable support С++17
-set(CMAKE_CXX_STANDARD 17)
-message(STATUS "Enabled С++17 support")
-
-# An interface library to make the target features available to other targets
-add_library(acore-feature-interface INTERFACE)
-
-target_compile_features(acore-feature-interface
-  INTERFACE
-    cxx_alias_templates
-    cxx_auto_type
-    cxx_constexpr
-    cxx_decltype
-    cxx_decltype_auto
-    cxx_final
-    cxx_lambdas
-    cxx_generic_lambdas
-    cxx_variadic_templates
-    cxx_defaulted_functions
-    cxx_nullptr
-    cxx_trailing_return_types
-    cxx_return_type_deduction)
+if (USE_CPP_20)
+  # Enable support С++20
+  set(CMAKE_CXX_STANDARD 20)
+  message(STATUS "Enabled С++20 standard")
+else()
+  # Enable support С++17
+  set(CMAKE_CXX_STANDARD 17)
+  message(STATUS "Enabled С++17 standard")
+endif()
 
 # An interface library to make the warnings level available to other targets
 # This interface taget is set-up through the platform specific script
@@ -38,10 +25,10 @@ add_library(acore-warning-interface INTERFACE)
 
 # An interface used for all other interfaces
 add_library(acore-default-interface INTERFACE)
+
 target_link_libraries(acore-default-interface
   INTERFACE
-    acore-compile-option-interface
-    acore-feature-interface)
+    acore-compile-option-interface)
 
 # An interface used for silencing all warnings
 add_library(acore-no-warning-interface INTERFACE)

src/cmake/showoptions.cmake

@@ -158,4 +158,10 @@ if(BUILD_SHARED_LIBS)
   WarnAboutSpacesInBuildPath()
 endif()
 
+if (USE_CPP_20)
+  message("")
+  message(" *** Enabled C++20 standart")
+  message(" *** Please note that this is an experimental feature!")
+endif()
+
 message("")