From 12bb88871e3cc4f52b3bc488ddc73389a7ac3b55 Mon Sep 17 00:00:00 2001
From: Niels Lohmann <mail@nlohmann.me>
Date: Wed, 20 Oct 2021 15:18:00 +0200
Subject: [PATCH] :alembic: do not use too old compilers with C++17

---
 include/nlohmann/detail/macro_scope.hpp | 2 +-
 single_include/nlohmann/json.hpp        | 2 +-
 test/CMakeLists.txt                     | 4 ++++
 test/src/unit-regression2.cpp           | 2 +-
 4 files changed, 7 insertions(+), 3 deletions(-)

diff --git a/include/nlohmann/detail/macro_scope.hpp b/include/nlohmann/detail/macro_scope.hpp
index 22c0ea525..e113ea573 100644
--- a/include/nlohmann/detail/macro_scope.hpp
+++ b/include/nlohmann/detail/macro_scope.hpp
@@ -54,7 +54,7 @@
     #endif
 
     // std::filesystem does not work on MinGW GCC 8: https://sourceforge.net/p/mingw-w64/bugs/737/
-    #if __MINGW32__ && __GNUC__ == 8
+    #if defined(__MINGW32__) && defined(__GNUC__) && __GNUC__ == 8
         #undef JSON_STD_FILESYSTEM_EXPERIMENTAL
     #endif
 #endif
diff --git a/single_include/nlohmann/json.hpp b/single_include/nlohmann/json.hpp
index 7e758f05f..4cb0056e5 100644
--- a/single_include/nlohmann/json.hpp
+++ b/single_include/nlohmann/json.hpp
@@ -2342,7 +2342,7 @@ using is_detected_convertible =
     #endif
 
     // std::filesystem does not work on MinGW GCC 8: https://sourceforge.net/p/mingw-w64/bugs/737/
-    #if __MINGW32__ && __GNUC__ == 8
+    #if defined(__MINGW32__) && defined(__GNUC__) && __GNUC__ == 8
         #undef JSON_STD_FILESYSTEM_EXPERIMENTAL
     #endif
 #endif
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index 5f681e5d0..0ab021051 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -58,6 +58,10 @@ foreach(feature ${CMAKE_CXX_COMPILE_FEATURES})
         set(compiler_supports_cpp_17 TRUE)
     endif()
 endforeach()
+# Clang only supports C++17 starting from Clang 5.0
+if ("${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)
 
diff --git a/test/src/unit-regression2.cpp b/test/src/unit-regression2.cpp
index fb8b268c6..292f5f04a 100644
--- a/test/src/unit-regression2.cpp
+++ b/test/src/unit-regression2.cpp
@@ -64,7 +64,7 @@ using ordered_json = nlohmann::ordered_json;
     #define JSON_STD_FILESYSTEM_EXPERIMENTAL 0
 
     // std::filesystem does not work on MinGW GCC 8: https://sourceforge.net/p/mingw-w64/bugs/737/
-    #if __MINGW32__ && __GNUC__ == 8
+    #if defined(__MINGW32__) && defined(__GNUC__) && __GNUC__ == 8
         #undef JSON_STD_FILESYSTEM_EXPERIMENTAL
     #endif
 #endif