Duplicate deregister in Nested Object GC

[chacha912]

What happened:

When performing garbage collection (GC) on nested objects, the deregister process leads to redundant operations on child nodes. This issue arises because the deregister iterates over children, while getDescendants also performs a similar traversal, resulting in unnecessary duplication.

yorkie-js-sdk/src/document/crdt/root.ts

Lines 168 to 191 in a714e66

	/**
	* `deregisterElement` deregister the given element and its descendants from hash table.
	*/
	public deregisterElement(element: CRDTElement): number {
	let count = 0;
	const deregisterElementInternal = (elem: CRDTElement) => {
	const createdAt = elem.getCreatedAt().toIDString();
	this.elementPairMapByCreatedAt.delete(createdAt);
	this.removedElementSetByCreatedAt.delete(createdAt);
	count++;
	if (elem instanceof CRDTContainer) {
	elem.getDescendants((e) => {
	deregisterElementInternal(e);
	return false;
	});
	}
	};
	deregisterElementInternal(element);
	return count;
	}

yorkie-js-sdk/src/document/crdt/object.ts

Lines 215 to 231 in a714e66

	/**
	* `getDescendants` returns the descendants of this object by traversing.
	*/
	public getDescendants(
	callback: (elem: CRDTElement, parent: CRDTContainer) => boolean,
	): void {
	for (const node of this.memberNodes) {
	const element = node.getValue();
	if (callback(element, this)) {
	return;
	}
	if (element instanceof CRDTContainer) {
	element.getDescendants(callback);
	}
	}
	}

What you expected to happen:

Garbage collection should efficiently iterate over children only once, deregistering them, and returning the accurate count of garbage-collected nodes.

How to reproduce it (as minimally and precisely as possible):

Execute the following test code:

it.only('test', async function ({ task }) {
  type TestDoc = { shape?: { point?: { x?: number; y?: number } } };
  const docKey = toDocKey(`${task.name}-${new Date().getTime()}`);
  const doc = new yorkie.Document<TestDoc>(docKey);

  doc.update((root) => {
    root.shape = { point: { x: 0, y: 0 } };
    delete root.shape;
  });
  assert.equal(doc.getGarbageLen(), 4); // shape, point, x, y
  assert.equal(doc.garbageCollect(MaxTimeTicket), 4); // The number of GC nodes must also be 4. (It's 6 for now.)
});

Anything else we need to know?:

This issue was reported in #714 .
The deregisterElements logic has been modified in #691 .

Environment:

• Operating system:
• Browser and version:
• Yorkie version (use yorkie version): v0.4.11
• Yorkie JS SDK version: v0.4.11