{"ast_node_type":"variable","tokens":[{"end":73,"kind":"keyword","start":0,"text":"let"}]}
                let cast_ty = fcx.resolve_vars_if_possible(self.cast_ty);
                let expr_if_nightly = fcx.tcx.sess.is_nightly_build().then_some(self.expr_span);
                let expr_ty = fcx.resolve_vars_if_possible(self.expr_ty);