Don't add partial objects when allocation fails

Fixes #2081

extras/tests/JsonVariant/add.cpp

@@ -6,6 +6,8 @@
 #include <stdint.h>
 #include <catch.hpp>
 
+#include "Allocators.hpp"
+
 TEST_CASE("JsonVariant::add(T)") {
   JsonDocument doc;
   JsonVariant var = doc.to<JsonVariant>();
@@ -56,15 +58,58 @@ TEST_CASE("JsonVariant::add<T>()") {
     REQUIRE(doc.as<std::string>() == "[[1,2]]");
   }
 
-  SECTION("JsonObject") {
-    JsonObject object = var.add<JsonObject>();
-    object["hello"] = "world";
-    REQUIRE(doc.as<std::string>() == "[{\"hello\":\"world\"}]");
-  }
-
   SECTION("JsonVariant") {
     JsonVariant variant = var.add<JsonVariant>();
     variant.set(42);
     REQUIRE(doc.as<std::string>() == "[42]");
   }
 }
+
+TEST_CASE("JsonObject::add(JsonObject) ") {
+  JsonDocument doc1;
+  doc1[std::string("hello")] = std::string("world");
+
+  TimebombAllocator allocator(10);
+  SpyingAllocator spy(&allocator);
+  JsonDocument doc2(&spy);
+  JsonVariant variant = doc2.to<JsonVariant>();
+
+  SECTION("success") {
+    bool result = variant.add(doc1.as<JsonObject>());
+
+    REQUIRE(result == true);
+    REQUIRE(doc2.as<std::string>() == "[{\"hello\":\"world\"}]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("hello")),
+                             Allocate(sizeofString("world")),
+                         });
+  }
+
+  SECTION("partial failure") {  // issue #2081
+    allocator.setCountdown(2);
+
+    bool result = variant.add(doc1.as<JsonObject>());
+
+    REQUIRE(result == false);
+    REQUIRE(doc2.as<std::string>() == "[]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             Allocate(sizeofPool()),
+                             Allocate(sizeofString("hello")),
+                             AllocateFail(sizeofString("world")),
+                             Deallocate(sizeofString("hello")),
+                         });
+  }
+
+  SECTION("complete failure") {
+    allocator.setCountdown(0);
+
+    bool result = variant.add(doc1.as<JsonObject>());
+
+    REQUIRE(result == false);
+    REQUIRE(doc2.as<std::string>() == "[]");
+    REQUIRE(spy.log() == AllocatorLog{
+                             AllocateFail(sizeofPool()),
+                         });
+  }
+}