error: failed to parse macro arguments: expected `Send`
 --> tests/ui/args_invalid.rs:3:20
  |
3 | #[async_recursion(?Sync)]
  |                    ^^^^

error: failed to parse macro arguments: expected `,`
 --> tests/ui/args_invalid.rs:6:24
  |
6 | #[async_recursion(Sync Sync)]
  |                        ^^^^

error: failed to parse macro arguments: expected `,`
 --> tests/ui/args_invalid.rs:9:23
  |
9 | #[async_recursion(Sync?Send)]
  |                       ^