{"ast_node_type":"variable","tokens":[{"end":87,"kind":"keyword","start":0,"text":"let"}]}
                            let (idx, _) = receiver.layout.non_1zst_field(self).expect(
                            // (The rules for `DispatchFromDyn` ensure there's exactly one such field.)
                                "not exactly one non-1-ZST field in a `DispatchFromDyn` type",