{"ast_node_type":"variable","tokens":[{"end":38,"kind":"keyword","start":0,"text":"let"}]}
        let fn_span = self.token.span;
    ) -> PResult<'a, (Ident, FnSig, Generics, Option<P<FnContract>>, Option<P<Block>>)> {
        let header = self.parse_fn_front_matter(vis, case, FrontMatterParsingMode::Function)?; // `const ... fn`