restore snapshot when parse_param_general

compiler/rustc_parse/src/parser/item.rs

@@ -2494,9 +2494,11 @@ impl<'a> Parser<'a> {
         // Parse the arguments, starting out with `self` being allowed...
         let (mut params, _) = self.parse_paren_comma_seq(|p| {
             p.recover_diff_marker();
+            let snapshot = p.create_snapshot_for_diagnostic();
             let param = p.parse_param_general(req_name, first_param).or_else(|mut e| {
                 e.emit();
                 let lo = p.prev_token.span;
+                p.restore_snapshot(snapshot);
                 // Skip every token until next possible arg or end.
                 p.eat_to_tokens(&[&token::Comma, &token::CloseDelim(Delimiter::Parenthesis)]);
                 // Create a placeholder argument for proper arg count (issue #34264).