Fix compatibility with GCC 5.2 (fixes #1897)

Author: bblanchon

CHANGELOG.md

@@ -5,6 +5,7 @@ HEAD
 ----
 
 * Double speed of `DynamicJsonDocument::garbageCollect()`
+* Fix compatibility with GCC 5.2 (issue #1897)
 
 v6.21.0 (2023-03-14)
 -------

extras/tests/JsonDeserializer/input_types.cpp

@@ -24,6 +24,30 @@ TEST_CASE("deserializeJson(char*)") {
   }
 }
 
+TEST_CASE("deserializeJson(unsigned char*, unsigned int)") {  // issue #1897
+  StaticJsonDocument<1024> doc;
+
+  unsigned char input[] = "{\"hello\":\"world\"}";
+  unsigned char* input_ptr = input;
+  unsigned int size = sizeof(input);
+
+  DeserializationError err = deserializeJson(doc, input_ptr, size);
+
+  REQUIRE(err == DeserializationError::Ok);
+}
+
+TEST_CASE("deserializeJson(uint8_t*, size_t)") {  // issue #1898
+  StaticJsonDocument<1024> doc;
+
+  uint8_t input[] = "{\"hello\":\"world\"}";
+  uint8_t* input_ptr = input;
+  size_t size = sizeof(input);
+
+  DeserializationError err = deserializeJson(doc, input_ptr, size);
+
+  REQUIRE(err == DeserializationError::Ok);
+}
+
 TEST_CASE("deserializeJson(const std::string&)") {
   DynamicJsonDocument doc(4096);
 

src/ArduinoJson/Deserialization/deserialize.hpp

@@ -12,6 +12,17 @@
 
 ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 
+// A meta-function that returns the first type of the parameter pack
+// or void if empty
+template <typename...>
+struct first_or_void {
+  using type = void;
+};
+template <typename T, typename... Rest>
+struct first_or_void<T, Rest...> {
+  using type = T;
+};
+
 template <template <typename, typename> class TDeserializer, typename TReader,
           typename TWriter>
 TDeserializer<TReader, TWriter> makeDeserializer(MemoryPool* pool,
@@ -22,7 +33,9 @@ TDeserializer<TReader, TWriter> makeDeserializer(MemoryPool* pool,
 }
 
 template <template <typename, typename> class TDeserializer, typename TStream,
-          typename... Args>
+          typename... Args,
+          typename = typename enable_if<  // issue #1897
+              !is_integral<typename first_or_void<Args...>::type>::value>::type>
 DeserializationError deserialize(JsonDocument& doc, TStream&& input,
                                  Args... args) {
   auto reader = makeReader(detail::forward<TStream>(input));