{"ast_node_type":"variable","tokens":[{"end":65,"kind":"keyword","start":0,"text":"let"}]}
        let a = self.type_checker.infcx.shallow_resolve_const(a);
    ) -> RelateResult<'tcx, ty::Const<'tcx>> {
        assert!(!a.has_non_region_infer(), "unexpected inference var {:?}", a);