{"ast_node_type":"variable","tokens":[{"end":79,"kind":"keyword","start":0,"text":"let"}]}
                            let (idx, _) = op.layout.non_1zst_field(bx).expect(
                        while !op.layout.ty.is_raw_ptr() && !op.layout.ty.is_ref() {
                                "not exactly one non-1-ZST field in a `DispatchFromDyn` type",