Add a stub for memoryUsage()

src/ArduinoJson/Array/JsonArray.hpp

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

src/ArduinoJson/Array/JsonArrayConst.hpp

@@ -78,6 +78,12 @@ class JsonArrayConst : public detail::VariantOperators<JsonArrayConst> {
     return data_ ? data_->size(resources_) : 0;
   }
 
+  // DEPRECATED: always returns zero
+  ARDUINOJSON_DEPRECATED("always returns zero")
+  size_t memoryUsage() const {
+    return 0;
+  }
+
  private:
   const detail::VariantData* getData() const {
     return collectionToVariant(data_);

src/ArduinoJson/Document/JsonDocument.hpp

@@ -291,6 +291,12 @@ class JsonDocument : public detail::VariantOperators<const JsonDocument&> {
     swap_(a.data_, b.data_);
   }
 
+  // DEPRECATED: always returns zero
+  ARDUINOJSON_DEPRECATED("always returns zero")
+  size_t memoryUsage() const {
+    return 0;
+  }
+
  private:
   JsonVariant getVariant() {
     return JsonVariant(&data_, &resources_);

src/ArduinoJson/Object/JsonObject.hpp

@@ -166,6 +166,12 @@ class JsonObject : public detail::VariantOperators<JsonObject> {
                                          resources_) != 0;
   }
 
+  // DEPRECATED: always returns zero
+  ARDUINOJSON_DEPRECATED("always returns zero")
+  size_t memoryUsage() const {
+    return 0;
+  }
+
  private:
   detail::ResourceManager* getResourceManager() const {
     return resources_;

src/ArduinoJson/Object/JsonObjectConst.hpp

@@ -105,6 +105,12 @@ class JsonObjectConst : public detail::VariantOperators<JsonObjectConst> {
         detail::ObjectData::getMember(data_, detail::adaptString(key)));
   }
 
+  // DEPRECATED: always returns zero
+  ARDUINOJSON_DEPRECATED("always returns zero")
+  size_t memoryUsage() const {
+    return 0;
+  }
+
  private:
   const detail::VariantData* getData() const {
     return collectionToVariant(data_);

src/ArduinoJson/Variant/JsonVariantConst.hpp

@@ -133,6 +133,12 @@ class JsonVariantConst : public detail::VariantTag,
                                           resources_) != 0;
   }
 
+  // DEPRECATED: always returns zero
+  ARDUINOJSON_DEPRECATED("always returns zero")
+  size_t memoryUsage() const {
+    return 0;
+  }
+
  protected:
   const detail::VariantData* getData() const {
     return data_;

src/ArduinoJson/Variant/VariantRefBase.hpp

@@ -221,6 +221,12 @@ class VariantRefBase : public VariantTag {
                                   MemberProxy<TDerived, TChar*>>::type
   operator[](TChar* key) const;
 
+  // DEPRECATED: always returns zero
+  ARDUINOJSON_DEPRECATED("always returns zero")
+  size_t memoryUsage() const {
+    return 0;
+  }
+
  private:
   TDerived& derived() {
     return static_cast<TDerived&>(*this);