过程宏如何检查Option<Option<T>>的泛型类型并将其展平为单个选项？

use syn::{parse_macro_input, DeriveInput};
use quote::quote;
use proc_macro::TokenStream;

#[proc_macro]
pub fn flatten_option(input: TokenStream) -> TokenStream {
    // 解析输入的语法树
    let input = parse_macro_input!(input as DeriveInput);

    // 获取泛型类型
    let inner_type = match input.generics.params.first() {
        Some(param) => quote!(#param),
        None => panic!("Expected a generic type parameter"),
    };

    // 生成展平后的代码
    let output = quote! {
        fn flatten_option(option: Option<Option<#inner_type>>) -> Option<#inner_type> {
            match option {
                Some(inner_option) => inner_option,
                None => None,
            }
        }
    };

    // 返回生成的代码
    output.into()
}

#[macro_use]
extern crate my_macro_crate;

fn main() {
    let option: Option<Option<i32>> = Some(Some(42));
    let flattened_option = flatten_option!(option);
    println!("{:?}", flattened_option); // 输出: Some(42)
}