src: refactor `BaseObject` internal field management

- Instead of storing a pointer whose type refers to the specific
  subclass of `BaseObject`, just store a `BaseObject*` directly.
  This means in particular that one can cast to classes along
  the way of the inheritance chain without issues, and that
  `BaseObject*` no longer needs to be the first superclass
  in the case of multiple inheritance.

  In particular, this renders hack-y solutions to this problem (like
  ddc19be6de1ba263d9c175b2760696e7b9918b25) obsolete and addresses
  a `TODO` comment of mine.

- Move wrapping/unwrapping methods to the `BaseObject` class.
  We use these almost exclusively for `BaseObject`s, and I hope
  that this gives a better idea of how (and for what) these are used
  in our code.

- Perform initialization/deinitialization of the internal field
  in the `BaseObject*` constructor/destructor. This makes the code
  a bit more obviously correct, avoids explicit calls for this
  in subclass constructors, and in particular allows us to avoid
  crash situations when we previously called `ClearWrap()`
  during GC.

  This also means that we enforce that the object passed to the
  `BaseObject` constructor needs to have an internal field.
  This is the only reason for the test change.

- Change the signature of `MakeWeak()` to not require a pointer
  argument. Previously, this would always have been the same
  as `this`, and no other value made sense. Also, the parameter
  was something that I personally found somewhat confusing
  when becoming familiar with Node’s code.

- Add a `TODO` comment that motivates switching to real inheritance
  for the JS types we expose from the native side. This patch
  brings us a lot closer to being able to do that.

- Some less significant drive-by cleanup.

Since we *effectively* already store the `BaseObject*` pointer
anyway since ddc19be6de1ba263d9c175b2760696e7b9918b25, I do not
think that this is going to have any impact on diagnostic tooling.

Fixes: https://github.com/nodejs/node/issues/18897
PR-URL: https://github.com/nodejs/node/pull/20455
Reviewed-By: Gus Caplan <me@gus.host>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Daniel Bevenius <daniel.bevenius@gmail.com>

1 files changed, 1 insertions, 15 deletions

diff --git a/src/udp_wrap.cc b/src/udp_wrap.cc
index e02220a8784..414fe07eab6 100644
--- a/src/udp_wrap.cc
+++ b/src/udp_wrap.cc
@@ -53,7 +53,6 @@ using AsyncHooks = Environment::AsyncHooks;
 class SendWrap : public ReqWrap<uv_udp_send_t> {
  public:
   SendWrap(Environment* env, Local<Object> req_wrap_obj, bool have_callback);
-  ~SendWrap();
   inline bool have_callback() const;
   size_t msg_size;
   size_t self_size() const override { return sizeof(*this); }
@@ -67,12 +66,6 @@ SendWrap::SendWrap(Environment* env,
                    bool have_callback)
     : ReqWrap(env, req_wrap_obj, AsyncWrap::PROVIDER_UDPSENDWRAP),
       have_callback_(have_callback) {
-  Wrap(req_wrap_obj, this);
-}
-
-
-SendWrap::~SendWrap() {
-  ClearWrap(object());
 }
 
 
@@ -81,12 +74,6 @@ inline bool SendWrap::have_callback() const {
 }
 
 
-static void NewSendWrap(const FunctionCallbackInfo<Value>& args) {
-  CHECK(args.IsConstructCall());
-  ClearWrap(args.This());
-}
-
-
 UDPWrap::UDPWrap(Environment* env, Local<Object> object)
     : HandleWrap(env,
                  object,
@@ -153,8 +140,7 @@ void UDPWrap::Initialize(Local<Object> target,
 
   // Create FunctionTemplate for SendWrap
   Local<FunctionTemplate> swt =
-      FunctionTemplate::New(env->isolate(), NewSendWrap);
-  swt->InstanceTemplate()->SetInternalFieldCount(1);
+      BaseObject::MakeLazilyInitializedJSTemplate(env);
   AsyncWrap::AddWrapMethods(env, swt);
   Local<String> sendWrapString =
       FIXED_ONE_BYTE_STRING(env->isolate(), "SendWrap");