Generic parameter of syn:Type

Hi all,

I have faced with issue how to get generic parameter for for result of parsed function:

async fn handle_url(url: Url, handled_urls: Arc<Mutex<HashSet<Url>>>)
    -> Result<(), IOError>
    // Some logic

And I try to parse this function with the following procedure macro:

    let input = syn::parse_macro_input!(item as syn::ItemFn);
    let attr_args = syn::parse_macro_input!(attrs as syn::AttributeArgs);

    let sig = &input.sig;
    let vis = input.vis;
    let name = &sig.ident;
    let mut args = Vec::new();
    for arg in &sig.inputs {
    let ret = match &sig.output {
        ReturnType::Default => {
            panic!("Used only for Result<?,?>");
        ReturnType::Type(arrow, box_type) => {
    match ret.as_ref() {
        Type::Path(type_path) => {
            println!("How to get Result<_,?> ?");
        _ => {
            panic!("Used only for Result<?,?>");
    let body = &input.block;
    let attrs = &input.attrs;

println!("How to get Result<_,?> ?"); shows the place where I cannot figure out the error of Result ...

Any help will be appreciated !!

Following the documentation, we get:

1 Like

One additional question ... do you know how to get crate where is the Type is defined ?

There is no way to do this, since macros are expanded before type resolution.

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