Implement nesting() out of VariantData

src/ArduinoJson/Variant/VariantFunctions.hpp

@@ -7,6 +7,7 @@
 #include <ArduinoJson/Polyfills/attributes.hpp>
 #include <ArduinoJson/Strings/StoragePolicy.hpp>
 #include <ArduinoJson/Variant/VariantData.hpp>
+#include <ArduinoJson/Variant/Visitor.hpp>
 
 namespace ARDUINOJSON_NAMESPACE {
 
@@ -106,4 +107,21 @@ inline bool variantIsNull(const VariantData *var) {
   return var == 0 || var->isNull();
 }
 
+inline size_t variantNesting(const VariantData *var) {
+  if (!var)
+    return 0;
+
+  const CollectionData *collection = var->asCollection();
+  if (!collection)
+    return 0;
+
+  size_t maxChildNesting = 0;
+  for (const VariantSlot *s = collection->head(); s; s = s->next()) {
+    size_t childNesting = variantNesting(s->data());
+    if (childNesting > maxChildNesting)
+      maxChildNesting = childNesting;
+  }
+  return maxChildNesting + 1;
+}
+
 }  // namespace ARDUINOJSON_NAMESPACE