Make JSON_STRING_SIZE(N) return N+1 to fix third-party code

ThingsBoard uses this macro to compute size of char arrays ಠ_ಠ
https://github.com/thingsboard/thingsboard-client-sdk/blob/v0.12.2/src/Helper.h#L38

Closes #2054

Author: bblanchon

CHANGELOG.md

@@ -1,6 +1,11 @@
 ArduinoJson: change log
 =======================
 
+HEAD
+----
+
+* Make `JSON_STRING_SIZE(N)` return `N+1` to fix third-party code (issue #2054)
+
 v7.0.3 (2024-02-05)
 ------
 

extras/tests/Deprecated/macros.cpp

@@ -14,5 +14,5 @@ TEST_CASE("JSON_OBJECT_SIZE") {
 }
 
 TEST_CASE("JSON_STRING_SIZE") {
-  REQUIRE(JSON_STRING_SIZE(10) == ArduinoJson::detail::sizeofString(10));
+  REQUIRE(JSON_STRING_SIZE(10) == 11);  // issue #2054
 }

src/ArduinoJson/compatibility.hpp

@@ -39,7 +39,7 @@
 #define JSON_OBJECT_SIZE(N) _Pragma ("GCC warning \"JSON_OBJECT_SIZE is deprecated, you don't need to compute the size anymore\"") (ArduinoJson::detail::sizeofObject(N))
 
 // DEPRECATED: you don't need to compute the size anymore
-#define JSON_STRING_SIZE(N) _Pragma ("GCC warning \"JSON_STRING_SIZE is deprecated, you don't need to compute the size anymore\"") (ArduinoJson::detail::sizeofString(N))
+#define JSON_STRING_SIZE(N) _Pragma ("GCC warning \"JSON_STRING_SIZE is deprecated, you don't need to compute the size anymore\"") (N+1)
 
 #else
 
@@ -50,7 +50,7 @@
 #define JSON_OBJECT_SIZE(N) (ArduinoJson::detail::sizeofObject(N))
 
 // DEPRECATED: you don't need to compute the size anymore
-#define JSON_STRING_SIZE(N) (ArduinoJson::detail::sizeofString(N))
+#define JSON_STRING_SIZE(N) (N+1)
 
 #endif