Prevent deregisterElement from deregistering twice in nested object

src/document/crdt/root.ts

@@ -176,16 +176,15 @@ export class CRDTRoot {
       this.elementPairMapByCreatedAt.delete(createdAt);
       this.removedElementSetByCreatedAt.delete(createdAt);
       count++;
-
-      if (elem instanceof CRDTContainer) {
-        elem.getDescendants((e) => {
-          deregisterElementInternal(e);
-          return false;
-        });
-      }
     };
 
     deregisterElementInternal(element);
+    if (element instanceof CRDTContainer) {
+      element.getDescendants((e) => {
+        deregisterElementInternal(e);
+        return false;
+      });
+    }
 
     return count;
   }

test/integration/gc_test.ts

@@ -682,4 +682,16 @@ describe('Garbage Collection', function () {
     await client1.deactivate();
     await client2.deactivate();
   });
+  it('garbage collection test for nested object', 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.
+  });
 });