Function rustc_builtin_macros::deriving::generic::cs_fold_fields

pub fn cs_fold_fields<'a, F>(
    use_foldl: bool, 
    f: F, 
    base: P<Expr>, 
    cx: &mut ExtCtxt<'_>, 
    all_fields: &[FieldInfo<'a>]
) -> P<Expr> where
    F: FnMut(&mut ExtCtxt<'_>, Span, P<Expr>, P<Expr>, &[P<Expr>]) -> P<Expr>,