improv: detect c++17 to define DPP_NO_CORO at the point of usage (#1378)

Author: Mishura4

.gitignore

@@ -12,6 +12,7 @@ buildtools/composer.phar
 src/build
 cmake-build-*
 docpages/example_code/build
+mlspp/include/namespace.h
 
 # tests
 test

include/dpp/coro/coro.h

@@ -20,6 +20,9 @@
  ************************************************************************************/
 
 #pragma once
+
+#include <dpp/export.h>
+
 #ifndef DPP_NO_CORO
 
 #if (defined(_LIBCPP_VERSION) and !defined(__cpp_impl_coroutine)) // if libc++ experimental implementation (LLVM < 14)

include/dpp/export.h

@@ -33,6 +33,15 @@
 	#error "D++ Requires a C++17 compatible C++ compiler. Please ensure that you have enabled C++17 in your compiler flags."
 #endif
 
+/* If not using c++20, define DPP_CPP17_COMPAT and DPP_NO_CORO.
+ */
+#if !(defined(__cplusplus) && __cplusplus >= 202002L) && !(defined(_MSVC_LANG) && _MSVC_LANG >= 202002L)
+#  define DPP_CPP17_COMPAT
+#  if !defined(DPP_CORO) || !DPP_CORO // Allow overriding this because why not
+#    define DPP_NO_CORO
+#  endif
+#endif
+
 #ifndef DPP_STATIC
 	/* Dynamic linked build as shared object or dll */
 	#ifdef DPP_BUILD

library/CMakeLists.txt

@@ -403,14 +403,16 @@ if(NOT DPP_NO_CORO)
 					if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 12.0.0)
 						message("${BoldRed}Clang with stdc++ and coroutines requires version 12.0.0 or above. Forcing coroutines off.${ColourReset}")
 						set(DPP_NO_CORO ON)
+					else()
+						message("-- ${Yellow}Detected stdc++ - enabling mock std::experimental namespace${ColourReset}")
+						target_compile_definitions(dpp PUBLIC "STDCORO_GLIBCXX_COMPAT" "DPP_CORO")
 					endif()
-					message("-- ${Yellow}Detected stdc++ - enabling mock std::experimental namespace${ColourReset}")
-					target_compile_definitions(dpp PUBLIC "STDCORO_GLIBCXX_COMPAT")
 				else()
 					message("-- ${Yellow}Detected libc++ - using <experimental/coroutine>${ColourReset}")
 					if(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 9.0.0)
 						set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fcoroutines-ts")
 					endif()
+					target_compile_definitions(dpp PUBLIC "STDCORO_GLIBCXX_COMPAT" "DPP_CORO")
 				endif()
 				message("-- ${Yellow}Note - coroutines in clang < 14 are experimental, upgrading is recommended${ColourReset}")
 			endif()
@@ -421,6 +423,7 @@ if(NOT DPP_NO_CORO)
 			elseif(CMAKE_CXX_COMPILER_VERSION VERSION_LESS 11.0)
 				message("-- ${Yellow}Note - coroutines in g++10 are experimental, upgrading to g++11 or above is recommended${ColourReset}")
 				set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fcoroutines")
+				target_compile_definitions(dpp PUBLIC "STDCORO_GLIBCXX_COMPAT" "DPP_CORO")
 			endif()
 		endif()
 	endif()

mlspp/include/namespace.h

@@ -1,4 +1,4 @@
-#pragma once
-
-// Configurable top-level MLS namespace
-#define MLS_NAMESPACE ../include/dpp/mlspp/mls
+#pragma once
+
+// Configurable top-level MLS namespace
+#define MLS_NAMESPACE mls