{"ast_node_type":"variable","tokens":[{"end":59,"kind":"keyword","start":0,"text":"let"}]}
            let category = if call_source.from_hir_call() {
            let op_arg_ty = self.normalize(op_arg_ty, term_location);
                ConstraintCategory::CallArgument(Some(self.infcx.tcx.erase_regions(func_ty)))