{"ast_node_type":"function","tokens":[{"end":34,"kind":"keyword","start":0,"text":"fn"}]}
    fn decode(d: &mut D) -> Self {
impl<D: Decoder, Prov: Provenance + Decodable<D>> Decodable<D> for ProvenanceMap<Prov> {
        assert!(!Prov::OFFSET_IS_ADDR); // only `CtfeProvenance` is ever serialized