{"ast_node_type":"variable","tokens":[{"end":97,"kind":"keyword","start":0,"text":"let"}]}
        let trait_ref = TraitRef { trait_id: to_chalk_trait_id(trait_id), substitution: substs };
        let substs = TyBuilder::placeholder_subst(db, trait_id);
        let pred = WhereClause::Implemented(trait_ref);