explicit fs tests, no c++ separate test

CMakeLists.txt

@@ -32,6 +32,7 @@ project(nana VERSION      1.7.2
 add_library(nana)
 add_library(nana::nana ALIAS nana)
 target_compile_features(nana PUBLIC cxx_std_17)
+# set(CMAKE_CXX_STANDARD 17)
 
 #  need after cxx_std_14 or cxx_std_17 ??
 target_compile_features(nana

build/cmake/select_filesystem.cmake

@@ -55,8 +55,6 @@ else()
     endif()
 
     check_include_file_cxx (filesystem              NANA_HAVE_FILESYSTEM)
-    check_include_file_cxx (experimental/filesystem NANA_HAVE_EXP_FILESYSTEM)
-
     if (NANA_HAVE_FILESYSTEM)
         message (STATUS "C++ Filesystem header:      <filesystem>")
         set (TEST_FS_LIB ON)
@@ -67,7 +65,9 @@ else()
                 std::filesystem::path p{\"\tmp/\"};
                 throw std::filesystem::filesystem_error(\"Empty file name!\", std::make_error_code(std::errc::invalid_argument));
             }")
-    elseif (NANA_HAVE_EXP_FILESYSTEM)
+    else()
+        check_include_file_cxx (experimental/filesystem NANA_HAVE_EXP_FILESYSTEM)
+        if (NANA_HAVE_EXP_FILESYSTEM)
             message (STATUS "C++ Filesystem header:      <experimental/filesystem>")
             set (TEST_FS_LIB ON)
             set (CXXSTD_FS_TEST_SOURCE
@@ -83,6 +83,7 @@ else()
             target_compile_definitions(nana PUBLIC STD_FILESYSTEM_NOT_SUPPORTED)
             set (TEST_FS_LIB OFF)
         endif ()
+    endif ()
 
     if (TEST_FS_LIB)
         include (FindPackageMessage)
@@ -94,56 +95,84 @@ else()
         set (CMAKE_REQUIRED_INCLUDES    ${CMAKE_INCLUDE_PATH})
         set (CMAKE_REQUIRED_FLAGS       ${CMAKE_CXX_FLAGS})
         set (CMAKE_REQUIRED_FLAGS_ORIGINAL ${CMAKE_REQUIRED_FLAGS})
-
-        set (CXXSTD_TEST_SOURCE
-                "#if !defined (__cplusplus) || (__cplusplus < 201703L)
-                #error NOCXX17
-                #endif
-                int main() {}")
-
-        check_cxx_source_compiles ("${CXXSTD_TEST_SOURCE}" CXX17_BUILTIN)
-
-        if (CXX17_BUILTIN)
-            message (STATUS "C++ Standard-17 support:    builtin")
-        else ()
-            set (CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS_ORIGINAL} -std=c++17")
-            check_cxx_source_compiles ("${CXXSTD_TEST_SOURCE}" CXX17_FLAG)
-            if (CXX17_FLAG)
-                message (STATUS "C++ Standard-17 support:    via -std=c++17")
-            else ()
-                message (WARNING "nana requires C++17??, but your compiler does not support it.")
-            endif ()
-        endif ()
-
         set (CMAKE_REQUIRED_LIBRARIES_ORIGINAL ${CMAKE_REQUIRED_LIBRARIES})
-        check_cxx_source_compiles ("${CXXSTD_TEST_SOURCE}" C++17FS_FLAG)
 
-        if (C++17FS_FLAG)
+        # c++: builtin
+        set (CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS_ORIGINAL}")
+        set (CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES_ORIGINAL})
+        check_cxx_source_compiles ("${CXXSTD_FS_TEST_SOURCE}" CXXBuiltIn_FS_BuiltIn)
+        if (CXXBuiltIn_FS_BuiltIn)
             message (STATUS "C++ Filesystem library:     builtin")
         else()
-            set (C++17FS_LIB "")
+            set (CMAKE_REQUIRED_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES_ORIGINAL} stdc++fs")
-            foreach (_LIB stdc++fs)
+            check_cxx_source_compiles ("${CXXSTD_FS_TEST_SOURCE}" CXXBuiltIn_FS_stdcppfs)
-                set (CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES_ORIGINAL} ${_LIB})
+            if (CXXBuiltIn_FS_stdcppfs)
-                check_cxx_source_compiles ("${CXXSTD_FS_TEST_SOURCE}" C++17FS_LIB-l${_LIB})
+                message (STATUS "C++ Filesystem library:     stdc++fs")
-                message (STATUS "C++ Filesystem library:    testing -l${_LIB}")
+                target_link_libraries     (nana PUBLIC stdc++fs)
-                if (C++17FS_LIB-l${_LIB})
+            else()
-                    target_link_libraries     (nana PUBLIC ${_LIB})
+                set (CMAKE_REQUIRED_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES_ORIGINAL} c++fs")
-                    message (STATUS "C++ Filesystem library:     via -l${_LIB}")
+                check_cxx_source_compiles ("${CXXSTD_FS_TEST_SOURCE}" CXXBuiltIn_FS_cppfs)
-                    set (C++17FS_LIB ${_LIB})
+                if (CXXBuiltIn_FS_cppfs)
-                    break ()
+                    message (STATUS "C++ Filesystem library:     c++fs")
-                endif ()
+                    target_link_libraries     (nana PUBLIC c++fs)
-                set (CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES_ORIGINAL})
+                else()
-            endforeach ()
+
+        # c++:   -std=c++17
+        set (CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS_ORIGINAL} -std=c++17")
+        set (CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES_ORIGINAL})
+        check_cxx_source_compiles ("${CXXSTD_FS_TEST_SOURCE}" CXX_std__cpp17_FS_BuiltIn)
+        if (CXX_std__cpp17_FS_BuiltIn)
+            message (STATUS "C++: -std=c++17; Filesystem library: builtin")
+        else()
+            set (CMAKE_REQUIRED_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES_ORIGINAL} stdc++fs")
+            check_cxx_source_compiles ("${CXXSTD_FS_TEST_SOURCE}" CXX_std__cpp17_FS_stdcppfs)
+            if (CXX_std__cpp17_FS_stdcppfs)
+                message (STATUS "C++: -std=c++17; Filesystem library:   stdc++fs")
+                target_link_libraries     (nana PUBLIC stdc++fs)
+            else()
+                set (CMAKE_REQUIRED_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES_ORIGINAL}  c++fs")
+                check_cxx_source_compiles ("${CXXSTD_FS_TEST_SOURCE}" CXX_std__cpp17_FS_cppfs)
+                if (CXX_std__cpp17_FS_cppfs)
+                    message (STATUS "C++: -std=c++17; Filesystem library:    c++fs")
+                    target_link_libraries     (nana PUBLIC  c++fs)
+                else()
+
+       # c++:   /std:c++17
+       set (CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS_ORIGINAL} /std:c++17")
+       set (CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES_ORIGINAL})
+       check_cxx_source_compiles ("${CXXSTD_FS_TEST_SOURCE}" CXX_std_cpp17_FS_BuiltIn)
+       if (CXX_std_cpp17_FS_BuiltIn)
+           message (STATUS "C++: /std:c++17; Filesystem library: builtin")
+       else()
+           set (CMAKE_REQUIRED_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES_ORIGINAL} stdc++fs")
+           check_cxx_source_compiles ("${CXXSTD_FS_TEST_SOURCE}" CXX_std_cpp17_FS_stdcppfs)
+           if (CXX_std_cpp17_FS_stdcppfs)
+               message (STATUS "C++: /std:c++17; Filesystem library:   stdc++fs")
+               target_link_libraries     (nana PUBLIC stdc++fs)
+           else()
+               set (CMAKE_REQUIRED_LIBRARIES "${CMAKE_REQUIRED_LIBRARIES_ORIGINAL}  c++fs")
+               check_cxx_source_compiles ("${CXXSTD_FS_TEST_SOURCE}" CXX_std_cpp17_FS_cppfs)
+               if (CXX_std_cpp17_FS_cppfs)
+                   message (STATUS "C++: /std:c++17; Filesystem library:    c++fs")
+                   target_link_libraries     (nana PUBLIC  c++fs)
 
-            if (C++17FS_LIB)
-                message (STATUS "C++ Filesystem library:     via -l${C++17FS_LIB}")
        else ()
             message (WARNING "No std::filesystem library found: nana::filesystem will be used.
                               Set NANA_CMAKE_NANA_FILESYSTEM_FORCE to ON to avoid this warning.")
             target_compile_definitions(nana PUBLIC STD_FILESYSTEM_NOT_SUPPORTED)
+            set (CMAKE_REQUIRED_LIBRARIES ${CMAKE_REQUIRED_LIBRARIES_ORIGINAL})
+        endif ()
+        endif ()
+        endif ()
+        endif ()
+        endif ()
         endif ()
         endif ()
         endif ()
         endif ()
 
+    endif (TEST_FS_LIB)
+endif ()
+
+