---@class with function return question

so I have this (as a mockup):

do
    ---@class a
    local a = {}

    ---@generic T
    ---@param self a
    ---@param new T
    ---@return T
    a.extend = function(self, new)
        --...
        return new
    end
end

and it's supposed to be inheritance for prototypes, right, but I'm trying to make the LS think that it returns the second parameter new and it does that and the LS thinks that, so far so good. So this

    local b = a:extend{
        n = 1
    }

will make it like this:

but the problem is, that if I use ---@class b here, then it will ignore what the function returns and I get this:

am I missing something or is it just not possible? Though, if I separate it into two statements like this,

    ---@class b
    local b = {
        n = 1
    }

    b = a:extend(b)

then I get what I want:

but it's not ideal, since it's two statements now and I can't use the fun{} syntactic sugar this way, which would be the whole reason, right. Is there a way to make it work? Also I'm unsure about how to properly word the title here

未指定源文件或测试。复现两个单行 Lua 代码片段和两个双语句 Lua 代码片段，然后跟踪 LuaLS 对局部声明、类注解、泛型和函数返回值的类型推断。实现受支持的行为并由回归测试覆盖，或明确记录该限制，即视为完成。