{"ast_node_type":"variable","tokens":[{"end":62,"kind":"keyword","start":0,"text":"let"}]}
        let parent_subst = ClosureSubst(subst).parent_subst();
        let (captures, _) = infer.closure_info(&c);
        captures.get(f).expect("broken closure field").ty.clone().substitute(Interner, parent_subst)