{"ast_node_type":"other","tokens":[{"end":71,"kind":"keyword","start":0,"text":"//"}]}
                    // it is of no concern, so we only check for TAITs.
                    // however in `fn fut() -> impl Future<Output = i32> { async { 42 } }`, where
                    if self.can_define_opaque_ty(b_def_id)