Fix missing collection of removed elements from the root

Sources/Document/Document.swift

@@ -344,6 +344,13 @@ public actor Document {
         return self.root.garbageLength
     }
 
+    /**
+     * `getGarbageLengthFromClone` returns the length of elements should be purged from clone.
+     */
+    func getGarbageLengthFromClone() -> Int {
+        return self.clone?.root.garbageLength ?? 0
+    }
+
     /**
      * `toJSON` returns the JSON encoding of this array.
      */

Sources/Document/Operation/SetOperation.swift

@@ -55,8 +55,11 @@ struct SetOperation: Operation {
         }
 
         let value = self.value.deepcopy()
-        parent.set(key: self.key, value: value)
+        let removed = parent.set(key: self.key, value: value)
         root.registerElement(value, parent: parent)
+        if let removed {
+            root.registerRemovedElement(removed)
+        }
 
         guard let path = try? root.createPath(createdAt: parentCreatedAt) else {
             throw YorkieError.unexpected(message: "fail to get path")

Tests/Integration/GCTests.swift

@@ -739,4 +739,34 @@ class GCTests: XCTestCase {
         try await client1.deactivate()
         try await client2.deactivate()
     }
+
+    func test_can_collect_removed_elements_from_both_root_and_clone() async throws {
+        let options = ClientOptions()
+        let docKey = "\(self.description)-\(Date().description)".toDocKey
+
+        let doc = Document(key: docKey)
+
+        let client = Client(rpcAddress: rpcAddress, options: options)
+
+        try await client.activate()
+
+        try await client.attach(doc, [:], false)
+
+        try await doc.update { root, _ in
+            root.point = ["x": Int64(0), "y": Int64(0)]
+        }
+
+        try await doc.update { root, _ in
+            root.point = ["x": Int64(1), "y": Int64(1)]
+        }
+
+        try await doc.update { root, _ in
+            root.point = ["x": Int64(2), "y": Int64(2)]
+        }
+
+        var len = await doc.getGarbageLength()
+        XCTAssertEqual(len, 6)
+        len = await doc.getGarbageLengthFromClone()
+        XCTAssertEqual(len, 6)
+    }
 }

Tests/Unit/Document/DocumentTests.swift

@@ -1049,7 +1049,7 @@ class DocumentTests: XCTestCase {
                        {}
                        """)
         var length = await target.getGarbageLength()
-        XCTAssertEqual(length, 1)
+        XCTAssertEqual(length, 2)
 
         await target.garbageCollect(lessThanOrEqualTo: TimeTicket.max)
         result = await target.toSortedJSON()