{"ast_node_type":"variable","tokens":[{"end":48,"kind":"keyword","start":0,"text":"let"}]}
        let ret_ty = callable_sig.ret().clone();
        let callable_sig = db.callable_item_signature(self.id.into()).substitute(Interner, &substs);
        for pred in ret_ty.impl_trait_bounds(db).into_iter().flatten() {