{"ast_node_type":"other","tokens":[{"end":88,"kind":"keyword","start":0,"text":"debug_assert!(!ty.is_ty_var(),"}]}
        debug_assert!(!ty.is_ty_var(), "instantiating ty var with var: {vid:?} {ty:?}");
        let vid = self.root_var(vid);
        debug_assert!(self.probe(vid).is_unknown());