src: fix cppgc incompatibility in v8

src/base_object.h

@@ -38,11 +38,18 @@ namespace worker {
 class TransferData;
 }
 
+// This just has to be different from the Chromium ones:
+// https://source.chromium.org/chromium/chromium/src/+/main:gin/public/gin_embedders.h;l=18-23;drc=5a758a97032f0b656c3c36a3497560762495501a
+// Otherwise, when Node is loaded in an isolate which uses cppgc, cppgc will
+// misinterpret the data stored in the embedder fields and try to garbage
+// collect them.
+static uint16_t kNodeEmbedderId = 0x90de;
+
 class BaseObject : public MemoryRetainer {
  public:
-  enum InternalFields { kSlot, kInternalFieldCount };
+  enum InternalFields { kEmbedderType, kSlot, kInternalFieldCount };
 
-  // Associates this object with `object`. It uses the 0th internal field for
+  // Associates this object with `object`. It uses the 1st internal field for
   // that, and in particular aborts if there is no such field.
   BaseObject(Environment* env, v8::Local<v8::Object> object);
   ~BaseObject() override;

src/env.cc

@@ -2126,7 +2126,9 @@ void Environment::RunWeakRefCleanup() {
 BaseObject::BaseObject(Environment* env, Local<Object> object)
     : persistent_handle_(env->isolate(), object), env_(env) {
   CHECK_EQ(false, object.IsEmpty());
-  CHECK_GT(object->InternalFieldCount(), 0);
+  CHECK_GE(object->InternalFieldCount(), BaseObject::kInternalFieldCount);
+  object->SetAlignedPointerInInternalField(BaseObject::kEmbedderType,
+                                           &kNodeEmbedderId);
   object->SetAlignedPointerInInternalField(BaseObject::kSlot,
                                            static_cast<void*>(this));
   env->AddCleanupHook(DeleteMe, static_cast<void*>(this));
@@ -2180,7 +2182,9 @@ void BaseObject::MakeWeak() {
 void BaseObject::LazilyInitializedJSTemplateConstructor(
     const FunctionCallbackInfo<Value>& args) {
   DCHECK(args.IsConstructCall());
-  DCHECK_GT(args.This()->InternalFieldCount(), 0);
+  CHECK_GE(args.This()->InternalFieldCount(), BaseObject::kInternalFieldCount);
+  args.This()->SetAlignedPointerInInternalField(BaseObject::kEmbedderType,
+                                                &kNodeEmbedderId);
   args.This()->SetAlignedPointerInInternalField(BaseObject::kSlot, nullptr);
 }