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,

doc/mkdocs/docs/features/macros.md

@@ -24,6 +24,13 @@ The diagnostics messages can also be controlled with the CMake option `JSON_Diag
 
 The library targets C++11, but also supports some features introduced in later C++ versions (e.g., `std::string_view` support for C++17). For these new features, the library implements some preprocessor checks to determine the C++ standard. By defining any of these symbols, the internal check is overridden and the provided C++ version is unconditionally assumed. This can be helpful for compilers that only implement parts of the standard and would be detected incorrectly.
 
+## `JSON_HAS_FILESYSTEM`, `JSON_HAS_EXPERIMENTAL_FILESYSTEM`
+
+When compiling with C++17, the library provides conversions from and to `std::filesystem::path`. As compiler support
+for filesystem is limited, the library tries to detect whether `<filesystem>`/`std::filesystem` (`JSON_HAS_FILESYSTEM`)
+or `<experimental/filesystem>`/`std::experimental::filesystem` (`JSON_HAS_EXPERIMENTAL_FILESYSTEM`) should be used.
+To override the built-in check, define `JSON_HAS_FILESYSTEM` or `JSON_HAS_EXPERIMENTAL_FILESYSTEM` to `1`.
+
 ## `JSON_NOEXCEPTION`
 
 Exceptions can be switched off by defining the symbol `JSON_NOEXCEPTION`.

include/nlohmann/detail/conversions/from_json.hpp

@@ -19,8 +19,18 @@
 #include <nlohmann/detail/meta/type_traits.hpp>
 #include <nlohmann/detail/value_t.hpp>
 
-#ifdef JSON_HAS_CPP_17
-    #include <filesystem>
+#if JSON_HAS_EXPERIMENTAL_FILESYSTEM
+#include <experimental/filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::experimental::filesystem;
+} // namespace nlohmann::detail
+#elif JSON_HAS_FILESYSTEM
+#include <filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::filesystem;
+} // namespace nlohmann::detail
 #endif
 
 namespace nlohmann
@@ -448,9 +458,9 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
     }
 }
 
-#ifdef JSON_HAS_CPP_17
+#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
 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 +15,18 @@
 #include <nlohmann/detail/meta/type_traits.hpp>
 #include <nlohmann/detail/value_t.hpp>
 
-#ifdef JSON_HAS_CPP_17
-    #include <filesystem>
+#if JSON_HAS_EXPERIMENTAL_FILESYSTEM
+#include <experimental/filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::experimental::filesystem;
+} // namespace nlohmann::detail
+#elif JSON_HAS_FILESYSTEM
+#include <filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::filesystem;
+} // namespace nlohmann::detail
 #endif
 
 namespace nlohmann
@@ -391,9 +401,9 @@ 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
+#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
 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 +37,66 @@
     #define JSON_HAS_CPP_11
 #endif
 
+#if !defined(JSON_HAS_FILESYSTEM) && !defined(JSON_HAS_EXPERIMENTAL_FILESYSTEM)
+    #ifdef JSON_HAS_CPP_17
+        #if defined(__cpp_lib_filesystem)
+            #define JSON_HAS_FILESYSTEM 1
+        #elif defined(__cpp_lib_experimental_filesystem)
+            #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
+        #elif !defined(__has_include)
+            #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
+        #elif __has_include(<filesystem>)
+            #define JSON_HAS_FILESYSTEM 1
+        #elif __has_include(<experimental/filesystem>)
+            #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
+        #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_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+
+        // no filesystem support before GCC 8: https://en.cppreference.com/w/cpp/compiler_support
+        #if defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 8
+            #undef JSON_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+
+        // no filesystem support before Clang 7: https://en.cppreference.com/w/cpp/compiler_support
+        #if defined(__clang_major__) && __clang_major__ < 7
+            #undef JSON_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+
+        // no filesystem support before MSVC 19.14: https://en.cppreference.com/w/cpp/compiler_support
+        #if defined(_MSC_VER) && _MSC_VER < 1940
+            #undef JSON_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+
+        // no filesystem support before iOS 13
+        #if defined(__IPHONE_OS_VERSION_MIN_REQUIRED) && __IPHONE_OS_VERSION_MIN_REQUIRED < 130000
+            #undef JSON_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+
+        // no filesystem support before macOS Catalina
+        #if defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && __MAC_OS_X_VERSION_MIN_REQUIRED < 101500
+            #undef JSON_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+    #endif
+#endif
+
+#ifndef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+    #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 0
+#endif
+
+#ifndef JSON_HAS_FILESYSTEM
+    #define JSON_HAS_FILESYSTEM 0
+#endif
+
 // disable documentation warnings on clang
 #if defined(__clang__)
     #pragma clang diagnostic push

include/nlohmann/detail/macro_unscope.hpp

@@ -16,6 +16,8 @@
 #undef JSON_HAS_CPP_14
 #undef JSON_HAS_CPP_17
 #undef JSON_HAS_CPP_20
+#undef JSON_HAS_FILESYSTEM
+#undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
 #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 +2325,66 @@ using is_detected_convertible =
     #define JSON_HAS_CPP_11
 #endif
 
+#if !defined(JSON_HAS_FILESYSTEM) && !defined(JSON_HAS_EXPERIMENTAL_FILESYSTEM)
+    #ifdef JSON_HAS_CPP_17
+        #if defined(__cpp_lib_filesystem)
+            #define JSON_HAS_FILESYSTEM 1
+        #elif defined(__cpp_lib_experimental_filesystem)
+            #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
+        #elif !defined(__has_include)
+            #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
+        #elif __has_include(<filesystem>)
+            #define JSON_HAS_FILESYSTEM 1
+        #elif __has_include(<experimental/filesystem>)
+            #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 1
+        #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_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+
+        // no filesystem support before GCC 8: https://en.cppreference.com/w/cpp/compiler_support
+        #if defined(__GNUC__) && !defined(__clang__) && __GNUC__ < 8
+            #undef JSON_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+
+        // no filesystem support before Clang 7: https://en.cppreference.com/w/cpp/compiler_support
+        #if defined(__clang_major__) && __clang_major__ < 7
+            #undef JSON_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+
+        // no filesystem support before MSVC 19.14: https://en.cppreference.com/w/cpp/compiler_support
+        #if defined(_MSC_VER) && _MSC_VER < 1940
+            #undef JSON_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+
+        // no filesystem support before iOS 13
+        #if defined(__IPHONE_OS_VERSION_MIN_REQUIRED) && __IPHONE_OS_VERSION_MIN_REQUIRED < 130000
+            #undef JSON_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+
+        // no filesystem support before macOS Catalina
+        #if defined(__MAC_OS_X_VERSION_MIN_REQUIRED) && __MAC_OS_X_VERSION_MIN_REQUIRED < 101500
+            #undef JSON_HAS_FILESYSTEM
+            #undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+        #endif
+    #endif
+#endif
+
+#ifndef JSON_HAS_EXPERIMENTAL_FILESYSTEM
+    #define JSON_HAS_EXPERIMENTAL_FILESYSTEM 0
+#endif
+
+#ifndef JSON_HAS_FILESYSTEM
+    #define JSON_HAS_FILESYSTEM 0
+#endif
+
 // disable documentation warnings on clang
 #if defined(__clang__)
     #pragma clang diagnostic push
@@ -3298,7 +3358,7 @@ 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 +4010,18 @@ T conditional_static_cast(U value)
 // #include <nlohmann/detail/value_t.hpp>
 
 
-#ifdef JSON_HAS_CPP_17
-    #include <filesystem>
+#if JSON_HAS_EXPERIMENTAL_FILESYSTEM
+#include <experimental/filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::experimental::filesystem;
+} // namespace nlohmann::detail
+#elif JSON_HAS_FILESYSTEM
+#include <filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::filesystem;
+} // namespace nlohmann::detail
 #endif
 
 namespace nlohmann
@@ -4379,9 +4449,9 @@ void from_json(const BasicJsonType& j, std::unordered_map<Key, Value, Hash, KeyE
     }
 }
 
-#ifdef JSON_HAS_CPP_17
+#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
 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 +4696,18 @@ class tuple_element<N, ::nlohmann::detail::iteration_proxy_value<IteratorType >>
 // #include <nlohmann/detail/value_t.hpp>
 
 
-#ifdef JSON_HAS_CPP_17
-    #include <filesystem>
+#if JSON_HAS_EXPERIMENTAL_FILESYSTEM
+#include <experimental/filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::experimental::filesystem;
+} // namespace nlohmann::detail
+#elif JSON_HAS_FILESYSTEM
+#include <filesystem>
+namespace nlohmann::detail
+{
+namespace std_fs = std::filesystem;
+} // namespace nlohmann::detail
 #endif
 
 namespace nlohmann
@@ -5002,9 +5082,9 @@ 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
+#if JSON_HAS_FILESYSTEM || JSON_HAS_EXPERIMENTAL_FILESYSTEM
 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 +26671,8 @@ 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_HAS_FILESYSTEM
+#undef JSON_HAS_EXPERIMENTAL_FILESYSTEM
 #undef NLOHMANN_BASIC_JSON_TPL_DECLARATION
 #undef NLOHMANN_BASIC_JSON_TPL
 #undef JSON_EXPLICIT

test/CMakeLists.txt

@@ -52,6 +52,21 @@ 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 ("${CMAKE_CXX_COMPILER_ID}" MATCHES "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 5.0)
+    unset(compiler_supports_cpp_17)
+endif()
+# MSVC 2015 (14.0) does not support C++17
+if ("${CMAKE_CXX_COMPILER_ID}" MATCHES "MSVC" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 19.1)
+    unset(compiler_supports_cpp_17)
+endif()
+
 file(GLOB files src/unit-*.cpp)
 
 foreach(file ${files})
@@ -68,6 +83,37 @@ 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(
         {