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, 3 insertions, 3 deletions

diff --git a/src/async_wrap.cc b/src/async_wrap.cc
index 06dcbb4fb1d..f7a6d4e68dd 100644
--- a/src/async_wrap.cc
+++ b/src/async_wrap.cc
@@ -123,8 +123,8 @@ RetainedObjectInfo* WrapperInfo(uint16_t class_id, Local<Value> wrapper) {
   Local<Object> object = wrapper.As<Object>();
   CHECK_GT(object->InternalFieldCount(), 0);
 
-  AsyncWrap* wrap = Unwrap<AsyncWrap>(object);
-  if (wrap == nullptr) return nullptr;  // ClearWrap() already called.
+  AsyncWrap* wrap;
+  ASSIGN_OR_RETURN_UNWRAP(&wrap, object, nullptr);
 
   return new RetainedAsyncInfo(class_id, wrap);
 }
@@ -231,7 +231,7 @@ class PromiseWrap : public AsyncWrap {
  public:
   PromiseWrap(Environment* env, Local<Object> object, bool silent)
       : AsyncWrap(env, object, PROVIDER_PROMISE, -1, silent) {
-    MakeWeak(this);
+    MakeWeak();
   }
   size_t self_size() const override { return sizeof(*this); }