Improve proc macro attribute diagnostics

Author: mejrs

proc_macro/src/lib.rs

@@ -74,6 +74,7 @@ pub fn is_available() -> bool {
 ///
 /// This is both the input and output of `#[proc_macro]`, `#[proc_macro_attribute]`
 /// and `#[proc_macro_derive]` definitions.
+#[rustc_diagnostic_item = "TokenStream"]
 #[stable(feature = "proc_macro_lib", since = "1.15.0")]
 #[derive(Clone)]
 pub struct TokenStream(Option<bridge::client::TokenStream>);