ScenePartition/Editor/ScenePartitionMenuEditor.cs

using UnityEditor;
using UnityEngine;

namespace VertexColor.ScenePartition.Editor
{
    public static class ScenePartitionMenuEditor
    {
        [MenuItem("GameObject/CopyFileId", false, 10000)]
        public static void CreateTextArea5()
        {
            GameObject go = Selection.activeGameObject;

            if (go == null) return;

            GlobalObjectId id = GlobalObjectId.GetGlobalObjectIdSlow(go);

            if (id.targetPrefabId == 0) // 0 = no prefab.
            {
                EditorGUIUtility.systemCopyBuffer = id.targetObjectId.ToString();
                Debug.Log($"object id: {id.targetObjectId}");
            }
            else
            {
                EditorGUIUtility.systemCopyBuffer = id.targetPrefabId.ToString();
                Debug.Log($"object id: {id.targetPrefabId}");
            }
        }
    }
}