Add C++17 copies of the test binaries

.clang-tidy

@@ -30,6 +30,7 @@ Checks: '*,
          -llvmlibc-*,
          -misc-no-recursion,
          -misc-non-private-member-variables-in-classes,
+         -modernize-use-nodiscard,
          -modernize-use-trailing-return-type,
          -readability-function-size,
          -readability-function-cognitive-complexity,

cmake/download_test_data.cmake

@@ -53,4 +53,4 @@ else()
     execute_process(COMMAND ${CMAKE_CXX_COMPILER} --version OUTPUT_VARIABLE CXX_VERSION_RESULT OUTPUT_STRIP_TRAILING_WHITESPACE)
 endif()
 string(REGEX REPLACE "[ ]*\n" "; " CXX_VERSION_RESULT "${CXX_VERSION_RESULT}")
-message(STATUS "Compiler: ${CXX_VERSION_RESULT}")
+message(STATUS "Compiler: ${CXX_VERSION_RESULT}, ${CMAKE_CXX_COMPILE_FEATURES}")

include/nlohmann/detail/conversions/from_json.hpp

@@ -19,8 +19,20 @@
 #include <nlohmann/detail/meta/type_traits.hpp>
 #include <nlohmann/detail/value_t.hpp>
 
-#ifdef JSON_HAS_CPP_17
-    #include <filesystem>
+#ifdef JSON_STD_FILESYSTEM_EXPERIMENTAL
+#if JSON_STD_FILESYSTEM_EXPERIMENTAL
+#include <experimental/filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::experimental::filesystem;
+} // namespace nlohmann::detail
+#else
+#include <filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::filesystem;
+} // namespace nlohmann::detail
+#endif
 #endif
 
 namespace nlohmann
@@ -448,9 +460,9 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
     }
 }
 
-#ifdef JSON_HAS_CPP_17
+#ifdef JSON_STD_FILESYSTEM_EXPERIMENTAL
 template<typename BasicJsonType>
-void from_json(const BasicJsonType& j, std::filesystem::path& p)
+void from_json(const BasicJsonType& j, std_fs::path& p)
 {
     if (JSON_HEDLEY_UNLIKELY(!j.is_string()))
     {

include/nlohmann/detail/conversions/to_json.hpp

@@ -15,8 +15,20 @@
 #include <nlohmann/detail/meta/type_traits.hpp>
 #include <nlohmann/detail/value_t.hpp>
 
-#ifdef JSON_HAS_CPP_17
-    #include <filesystem>
+#ifdef JSON_STD_FILESYSTEM_EXPERIMENTAL
+#if JSON_STD_FILESYSTEM_EXPERIMENTAL
+#include <experimental/filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::experimental::filesystem;
+} // namespace nlohmann::detail
+#else
+#include <filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::filesystem;
+} // namespace nlohmann::detail
+#endif
 #endif
 
 namespace nlohmann
@@ -391,9 +403,9 @@ void to_json(BasicJsonType& j, const T& t)
     to_json_tuple_impl(j, t, make_index_sequence<std::tuple_size<T>::value> {});
 }
 
-#ifdef JSON_HAS_CPP_17
+#ifdef JSON_STD_FILESYSTEM_EXPERIMENTAL
 template<typename BasicJsonType>
-void to_json(BasicJsonType& j, const std::filesystem::path& p)
+void to_json(BasicJsonType& j, const std_fs::path& p)
 {
     j = p.string();
 }

include/nlohmann/detail/macro_scope.hpp

@@ -37,6 +37,28 @@
     #define JSON_HAS_CPP_11
 #endif
 
+#ifdef JSON_HAS_CPP_17
+    // set JSON_STD_FILESYSTEM_EXPERIMENTAL to 1 if <experimental/filesystem> should be taken instead of <filesystem>
+    #if defined(__cpp_lib_filesystem)
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 0
+    #elif defined(__cpp_lib_experimental_filesystem)
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 1
+    #elif !defined(__has_include)
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 1
+    #elif __has_include(<filesystem>)
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 0
+    #elif __has_include(<experimental/filesystem>)
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 1
+    #else
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 0
+    #endif
+
+    // std::filesystem does not work on MinGW GCC 8: https://sourceforge.net/p/mingw-w64/bugs/737/
+    #if defined(__MINGW32__) && defined(__GNUC__) && __GNUC__ == 8
+        #undef JSON_STD_FILESYSTEM_EXPERIMENTAL
+    #endif
+#endif
+
 // disable documentation warnings on clang
 #if defined(__clang__)
     #pragma clang diagnostic push

include/nlohmann/detail/macro_unscope.hpp

@@ -16,6 +16,7 @@
 #undef JSON_HAS_CPP_14
 #undef JSON_HAS_CPP_17
 #undef JSON_HAS_CPP_20
+#undef JSON_STD_FILESYSTEM_EXPERIMENTAL
 #undef NLOHMANN_BASIC_JSON_TPL_DECLARATION
 #undef NLOHMANN_BASIC_JSON_TPL
 #undef JSON_EXPLICIT

include/nlohmann/detail/meta/cpp_future.hpp

@@ -148,7 +148,7 @@ struct static_const
 };
 
 template<typename T>
-constexpr T static_const<T>::value;
+constexpr T static_const<T>::value; // NOLINT(readability-redundant-declaration)
 
 }  // namespace detail
 }  // namespace nlohmann

single_include/nlohmann/json.hpp

@@ -2325,6 +2325,28 @@ using is_detected_convertible =
     #define JSON_HAS_CPP_11
 #endif
 
+#ifdef JSON_HAS_CPP_17
+    // set JSON_STD_FILESYSTEM_EXPERIMENTAL to 1 if <experimental/filesystem> should be taken instead of <filesystem>
+    #if defined(__cpp_lib_filesystem)
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 0
+    #elif defined(__cpp_lib_experimental_filesystem)
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 1
+    #elif !defined(__has_include)
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 1
+    #elif __has_include(<filesystem>)
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 0
+    #elif __has_include(<experimental/filesystem>)
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 1
+    #else
+        #define JSON_STD_FILESYSTEM_EXPERIMENTAL 0
+    #endif
+
+    // std::filesystem does not work on MinGW GCC 8: https://sourceforge.net/p/mingw-w64/bugs/737/
+    #if defined(__MINGW32__) && defined(__GNUC__) && __GNUC__ == 8
+        #undef JSON_STD_FILESYSTEM_EXPERIMENTAL
+    #endif
+#endif
+
 // disable documentation warnings on clang
 #if defined(__clang__)
     #pragma clang diagnostic push
@@ -3298,7 +3320,7 @@ struct static_const
 };
 
 template<typename T>
-constexpr T static_const<T>::value;
+constexpr T static_const<T>::value; // NOLINT(readability-redundant-declaration)
 
 }  // namespace detail
 }  // namespace nlohmann
@@ -3950,8 +3972,20 @@ T conditional_static_cast(U value)
 // #include <nlohmann/detail/value_t.hpp>
 
 
-#ifdef JSON_HAS_CPP_17
-    #include <filesystem>
+#ifdef JSON_STD_FILESYSTEM_EXPERIMENTAL
+#if JSON_STD_FILESYSTEM_EXPERIMENTAL
+#include <experimental/filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::experimental::filesystem;
+} // namespace nlohmann::detail
+#else
+#include <filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::filesystem;
+} // namespace nlohmann::detail
+#endif
 #endif
 
 namespace nlohmann
@@ -4379,9 +4413,9 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
     }
 }
 
-#ifdef JSON_HAS_CPP_17
+#ifdef JSON_STD_FILESYSTEM_EXPERIMENTAL
 template<typename BasicJsonType>
-void from_json(const BasicJsonType& j, std::filesystem::path& p)
+void from_json(const BasicJsonType& j, std_fs::path& p)
 {
     if (JSON_HEDLEY_UNLIKELY(!j.is_string()))
     {
@@ -4626,8 +4660,20 @@ class tuple_element<N, ::nlohmann::detail::iteration_proxy_value<IteratorType >>
 // #include <nlohmann/detail/value_t.hpp>
 
 
-#ifdef JSON_HAS_CPP_17
-    #include <filesystem>
+#ifdef JSON_STD_FILESYSTEM_EXPERIMENTAL
+#if JSON_STD_FILESYSTEM_EXPERIMENTAL
+#include <experimental/filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::experimental::filesystem;
+} // namespace nlohmann::detail
+#else
+#include <filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::filesystem;
+} // namespace nlohmann::detail
+#endif
 #endif
 
 namespace nlohmann
@@ -5002,9 +5048,9 @@ void to_json(BasicJsonType& j, const T& t)
     to_json_tuple_impl(j, t, make_index_sequence<std::tuple_size<T>::value> {});
 }
 
-#ifdef JSON_HAS_CPP_17
+#ifdef JSON_STD_FILESYSTEM_EXPERIMENTAL
 template<typename BasicJsonType>
-void to_json(BasicJsonType& j, const std::filesystem::path& p)
+void to_json(BasicJsonType& j, const std_fs::path& p)
 {
     j = p.string();
 }
@@ -26591,6 +26637,7 @@ inline nlohmann::json::json_pointer operator "" _json_pointer(const char* s, std
 #undef JSON_HAS_CPP_14
 #undef JSON_HAS_CPP_17
 #undef JSON_HAS_CPP_20
+#undef JSON_STD_FILESYSTEM_EXPERIMENTAL
 #undef NLOHMANN_BASIC_JSON_TPL_DECLARATION
 #undef NLOHMANN_BASIC_JSON_TPL
 #undef JSON_EXPLICIT

test/CMakeLists.txt

@@ -52,6 +52,17 @@ endif()
 # one executable for each unit test file
 #############################################################################
 
+# check if compiler supports C++17
+foreach(feature ${CMAKE_CXX_COMPILE_FEATURES})
+    if (${feature} STREQUAL cxx_std_17)
+        set(compiler_supports_cpp_17 TRUE)
+    endif()
+endforeach()
+# Clang only supports C++17 starting from Clang 5.0
+if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)
+    unset(compiler_supports_cpp_17)
+endif()
+
 file(GLOB files src/unit-*.cpp)
 
 foreach(file ${files})
@@ -68,6 +79,37 @@ foreach(file ${files})
     target_include_directories(${testcase} PRIVATE ${CMAKE_BINARY_DIR}/include thirdparty/doctest thirdparty/fifo_map)
     target_link_libraries(${testcase} PRIVATE ${NLOHMANN_JSON_TARGET_NAME})
 
+    # add a copy with C++17 compilation
+    if (compiler_supports_cpp_17)
+        file(READ ${file} FILE_CONTENT)
+        string(FIND "${FILE_CONTENT}" "JSON_HAS_CPP_17" CPP_17_FOUND)
+        if(NOT ${CPP_17_FOUND} EQUAL -1)
+            add_executable(${testcase}_cpp17 $<TARGET_OBJECTS:doctest_main> ${file})
+            target_compile_definitions(${testcase}_cpp17 PRIVATE DOCTEST_CONFIG_SUPER_FAST_ASSERTS)
+            target_compile_options(${testcase}_cpp17 PRIVATE
+                $<$<CXX_COMPILER_ID:MSVC>:/EHsc;$<$<CONFIG:Release>:/Od>>
+                $<$<NOT:$<CXX_COMPILER_ID:MSVC>>:-Wno-deprecated;-Wno-float-equal>
+                $<$<CXX_COMPILER_ID:GNU>:-Wno-deprecated-declarations>
+            )
+            target_include_directories(${testcase}_cpp17 PRIVATE ${CMAKE_BINARY_DIR}/include thirdparty/doctest thirdparty/fifo_map)
+            target_link_libraries(${testcase}_cpp17 PRIVATE ${NLOHMANN_JSON_TARGET_NAME})
+            target_compile_features(${testcase}_cpp17 PRIVATE cxx_std_17)
+
+            if (JSON_FastTests)
+                add_test(NAME "${testcase}_cpp17"
+                    COMMAND ${testcase}_cpp17 ${DOCTEST_TEST_FILTER}
+                    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
+                )
+            else()
+                add_test(NAME "${testcase}_cpp17"
+                    COMMAND ${testcase}_cpp17 ${DOCTEST_TEST_FILTER} --no-skip
+                    WORKING_DIRECTORY ${CMAKE_SOURCE_DIR}
+                )
+            endif()
+            set_tests_properties("${testcase}_cpp17" PROPERTIES LABELS "all" FIXTURES_REQUIRED TEST_DATA)
+        endif()
+    endif()
+
     if (JSON_FastTests)
         add_test(NAME "${testcase}"
             COMMAND ${testcase} ${DOCTEST_TEST_FILTER}

test/src/unit-regression1.cpp

@@ -205,7 +205,7 @@ TEST_CASE("regression tests 1")
         // check if the actual value was stored
         CHECK(j2 == 102);
 
-        static_assert(std::is_same<decltype(anon_enum_value), decltype(u)>::value, "");
+        static_assert(std::is_same<decltype(anon_enum_value), decltype(u)>::value, "types must be the same");
 
         j.push_back(json::object(
         {