Call shrinkToFit() in deserializeJson() and deserializeMsgPack()

src/ArduinoJson/Configuration.hpp

@@ -110,6 +110,17 @@
 #  define ARDUINOJSON_INITIAL_POOL_COUNT 4
 #endif
 
+// Automatically call shrinkToFit() from deserializeXxx()
+// Disabled by default on 8-bit platforms because it's not worth the increase in
+// code size
+#ifndef ARDUINOJSON_AUTO_SHRINK
+#  if defined(__SIZEOF_POINTER__) && __SIZEOF_POINTER__ <= 2
+#    define ARDUINOJSON_AUTO_SHRINK 0
+#  else
+#    define ARDUINOJSON_AUTO_SHRINK 1
+#  endif
+#endif
+
 #ifdef ARDUINO
 
 // Enable support for Arduino's String class

src/ArduinoJson/Deserialization/Filter.hpp

@@ -4,14 +4,21 @@
 
 #pragma once
 
-#include <ArduinoJson/Namespace.hpp>
+#include <ArduinoJson/Variant/JsonVariant.hpp>
+#include <ArduinoJson/Variant/VariantAttorney.hpp>
 
 ARDUINOJSON_BEGIN_PUBLIC_NAMESPACE
 
 namespace DeserializationOption {
 class Filter {
  public:
-  explicit Filter(JsonVariantConst v) : variant_(v) {}
+#if ARDUINOJSON_AUTO_SHRINK
+  explicit Filter(JsonDocument& doc) : variant_(doc) {
+    doc.shrinkToFit();
+  }
+#endif
+
+  explicit Filter(JsonVariantConst variant) : variant_(variant) {}
 
   bool allow() const {
     return variant_;

src/ArduinoJson/Deserialization/deserialize.hpp

@@ -43,8 +43,12 @@ DeserializationError doDeserialize(TDestination&& dst, TReader reader,
     return DeserializationError::NoMemory;
   auto resources = VariantAttorney::getResourceManager(dst);
   dst.clear();
-  return TDeserializer<TReader>(resources, reader)
-      .parse(*data, options.filter, options.nestingLimit);
+  auto err = TDeserializer<TReader>(resources, reader)
+                 .parse(*data, options.filter, options.nestingLimit);
+#if ARDUINOJSON_AUTO_SHRINK
+  resources->shrinkToFit();
+#endif
+  return err;
 }
 
 template <template <typename> class TDeserializer, typename TDestination,

src/ArduinoJson/Memory/VariantPoolImpl.hpp

@@ -26,9 +26,12 @@ inline void VariantPool::destroy(Allocator* allocator) {
 }
 
 inline void VariantPool::shrinkToFit(Allocator* allocator) {
-  slots_ = reinterpret_cast<VariantSlot*>(
+  auto newSlots = reinterpret_cast<VariantSlot*>(
       allocator->reallocate(slots_, slotsToBytes(usage_)));
-  capacity_ = usage_;
+  if (newSlots) {
+    slots_ = newSlots;
+    capacity_ = usage_;
+  }
 }
 
 inline SlotWithId VariantPool::allocSlot() {