Fixed error expected unqualified-id on GCC 11 (fixes #1622)

extras/tests/CMakeLists.txt

@@ -12,6 +12,7 @@ link_libraries(ArduinoJson catch)
 include_directories(Helpers)
 add_subdirectory(Cpp11)
 add_subdirectory(Cpp17)
+add_subdirectory(Cpp20)
 add_subdirectory(FailingBuilds)
 add_subdirectory(IntegrationTests)
 add_subdirectory(JsonArray)

extras/tests/Cpp20/CMakeLists.txt

@@ -0,0 +1,29 @@
+# ArduinoJson - https://arduinojson.org
+# Copyright Benoit Blanchon 2014-2021
+# MIT License
+
+if(MSVC_VERSION LESS 1910)
+	return()
+endif()
+
+if(CMAKE_CXX_COMPILER_ID MATCHES "Clang" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 10)
+	return()
+endif()
+
+if(CMAKE_CXX_COMPILER_ID STREQUAL "GNU" AND CMAKE_CXX_COMPILER_VERSION VERSION_LESS 10)
+	return()
+endif()
+
+set(CMAKE_CXX_STANDARD 20)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+
+add_executable(Cpp20Tests
+	smoke_test.cpp
+)
+
+add_test(Cpp20 Cpp20Tests)
+
+set_tests_properties(Cpp20
+	PROPERTIES
+		LABELS 		"Catch"
+)

extras/tests/Cpp20/smoke_test.cpp

@@ -0,0 +1,15 @@
+#include <ArduinoJson.h>
+
+#include <catch.hpp>
+#include <string>
+
+TEST_CASE("C++20 smoke test") {
+  StaticJsonDocument<128> doc;
+
+  deserializeJson(doc, "{\"hello\":\"world\"}");
+  REQUIRE(doc["hello"] == "world");
+
+  std::string json;
+  serializeJson(doc, json);
+  REQUIRE(json == "{\"hello\":\"world\"}");
+}