Diffirintiate between index and newindex

Will it be possible to set different types for index and newindex metamethods?

My use case is tree structure that return new tree_node from index and stores data when newindex is called.

If I use generic {[key]:new_index_type} it works almost fine but index return incorrect types.

Below is example of what I'm trying to achive

该 issue 提到了 __index 和 __newindex 元方法，并展示了一个 tree_node 使用场景，但没有指出源文件或测试。首先定位这些元方法的类型推断处理，并复现报告中的泛型表行为。当 index 和 newindex 能够接收不同的类型且不破坏示例时，即视为完成。