{"ast_node_type":"other","tokens":[{"end":86,"kind":"keyword","start":0,"text":"//"}]}
        // existential type AsyncBlockImplTrait<InnerType>: Future<Output = InnerType>
        // Use the first type parameter as the output type of future.
        let impl_trait_id = crate::ImplTraitId::AsyncBlockTypeImplTrait(self.owner, tgt_expr);