{"ast_node_type":"variable","tokens":[{"end":50,"kind":"keyword","start":0,"text":"let"}]}
            let expected_ty = ecx.next_ty_infer();
        ecx.probe_builtin_trait_candidate(BuiltinImplSource::Misc).enter(|ecx| {
            // Take `AsyncIterator<Item = I>` and turn it into the corresponding