Error parsing Option<()> and Result<(), ()> literals in syn::parse_macro_input: unexpected end of input, expected an expression #1726
Description
I'm having issues with handling Option::<()>::Some(()) and Result::<(), ()>::Ok(()) literals in my macro.
Below is the gist of the macro that I've implemented, doesn't really stray from the documentation:
use syn::punctuated::Punctuated;
use syn::parse::{Parse, ParseStream};
use syn::{parse_macro_input, Token, Expr};
struct Args {
args: Punctuated<Expr, Token![,]>,
}
impl Parse for Args {
fn parse(input: ParseStream) -> syn::Result<Self> {
Ok(Self { args: Punctuated::<Expr, Token![,]>::parse_terminated(input)? })
}
}
#[proc_macro]
pub fn foo(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
let args = parse_macro_input!(input as Args); // __this is where it fails__
// ...
}I have a proc_macro2 test that also confirms this behavior with both std prelude and fully qualified forms:
// Fails with Some(())...
syn::parse_macro_input(proc_macro2::TokenStream::from_str("Some(())").unwrap()); // error: expected '()', found 'TokenStream'
syn::parse_macro_input(proc_macro2::TokenStream::from_str("Option::<()>::Some(())").unwrap()); // error: expected '()', found 'TokenStream'
// and with Ok(())
syn::parse_macro_input(proc_macro2::TokenStream::from_str("Ok(())").unwrap()); // error: expected '()', found 'TokenStream'
syn::parse_macro_input(proc_macro2::TokenStream::from_str("Result::<(), ()>::Ok(())").unwrap()); // error: expected '()', found 'TokenStream'The error that gets emitted from these tests is expected '()', found 'TokenStream'