Add a stub for add()

extras/tests/Deprecated/CMakeLists.txt

@@ -15,6 +15,7 @@ if(MSVC)
 endif()
 
 add_executable(DeprecatedTests
+	add.cpp
 	BasicJsonDocument.cpp
 	DynamicJsonDocument.cpp
 	memoryUsage.cpp

extras/tests/Deprecated/add.cpp

@@ -0,0 +1,38 @@
+// ArduinoJson - https://arduinojson.org
+// Copyright © 2014-2023, Benoit BLANCHON
+// MIT License
+
+#include <ArduinoJson.h>
+#include <catch.hpp>
+
+TEST_CASE("JsonArray::add()") {
+  JsonDocument doc;
+  JsonArray array = doc.to<JsonArray>();
+  array.add().set(42);
+  REQUIRE(doc.as<std::string>() == "[42]");
+}
+
+TEST_CASE("JsonDocument::add()") {
+  JsonDocument doc;
+  doc.add().set(42);
+  REQUIRE(doc.as<std::string>() == "[42]");
+}
+
+TEST_CASE("ElementProxy::add()") {
+  JsonDocument doc;
+  doc[0].add().set(42);
+  REQUIRE(doc.as<std::string>() == "[[42]]");
+}
+
+TEST_CASE("MemberProxy::add()") {
+  JsonDocument doc;
+  doc["x"].add().set(42);
+  REQUIRE(doc.as<std::string>() == "{\"x\":[42]}");
+}
+
+TEST_CASE("JsonVariant::add()") {
+  JsonDocument doc;
+  JsonVariant v = doc.add();
+  v.add().set(42);
+  REQUIRE(doc.as<std::string>() == "[[42]]");
+}

src/ArduinoJson/Array/JsonArray.hpp

@@ -158,6 +158,12 @@ class JsonArray : public detail::VariantOperators<JsonArray> {
     return data_ ? data_->size(resources_) : 0;
   }
 
+  // DEPRECATED: use add<JsonVariant>() instead
+  ARDUINOJSON_DEPRECATED("use add<JsonVariant>() instead")
+  JsonVariant add() const {
+    return add<JsonVariant>();
+  }
+
   // DEPRECATED: always returns zero
   ARDUINOJSON_DEPRECATED("always returns zero")
   size_t memoryUsage() const {

src/ArduinoJson/Document/JsonDocument.hpp

@@ -291,6 +291,12 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
     swap_(a.data_, b.data_);
   }
 
+  // DEPRECATED: use add<JsonVariant>() instead
+  ARDUINOJSON_DEPRECATED("use add<JsonVariant>() instead")
+  JsonVariant add() {
+    return add<JsonVariant>();
+  }
+
   // DEPRECATED: always returns zero
   ARDUINOJSON_DEPRECATED("always returns zero")
   size_t memoryUsage() const {

src/ArduinoJson/Variant/VariantRefBase.hpp

@@ -221,6 +221,10 @@ class VariantRefBase : public VariantTag {
                                   MemberProxy<TDerived, TChar*>>::type
   operator[](TChar* key) const;
 
+  // DEPRECATED: use add<JsonVariant>() instead
+  ARDUINOJSON_DEPRECATED("use add<JsonVariant>() instead")
+  JsonVariant add() const;
+
   // DEPRECATED: always returns zero
   ARDUINOJSON_DEPRECATED("always returns zero")
   size_t memoryUsage() const {

src/ArduinoJson/Variant/VariantRefBaseImpl.hpp

@@ -10,6 +10,11 @@
 
 ARDUINOJSON_BEGIN_PRIVATE_NAMESPACE
 
+template <typename TDerived>
+inline JsonVariant VariantRefBase<TDerived>::add() const {
+  return add<JsonVariant>();
+}
+
 template <typename TDerived>
 inline void convertToJson(const VariantRefBase<TDerived>& src,
                           JsonVariant dst) {