🏁 fix <optional> inclusion

include/nlohmann/detail/conversions/from_json.hpp

@@ -14,7 +14,11 @@
 #include <valarray> // valarray
 
 #ifdef JSON_HAS_CPP_17
-    #include <optional> // optional
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
 #endif
 
 #include <nlohmann/detail/exceptions.hpp>

include/nlohmann/detail/conversions/to_json.hpp

@@ -11,7 +11,11 @@
 #include <vector> // vector
 
 #ifdef JSON_HAS_CPP_17
-    #include <optional> // optional
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
 #endif
 
 #include <nlohmann/detail/iterators/iteration_proxy.hpp>

single_include/nlohmann/json.hpp

@@ -70,7 +70,11 @@ SOFTWARE.
 #include <valarray> // valarray
 
 #ifdef JSON_HAS_CPP_17
-    #include <optional> // optional
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
 #endif
 
 // #include <nlohmann/detail/exceptions.hpp>
@@ -3292,7 +3296,11 @@ constexpr const auto& from_json = detail::static_const<detail::from_json_fn>::va
 #include <vector> // vector
 
 #ifdef JSON_HAS_CPP_17
-    #include <optional> // optional
+    #if __has_include(<optional>)
+        #include <optional>
+    #elif __has_include(<experimental/optional>)
+        #include <experimental/optional>
+    #endif
 #endif
 
 // #include <nlohmann/detail/iterators/iteration_proxy.hpp>