Function decode_datum_with_codec_and_limits 

pub fn decode_datum_with_codec_and_limits(
    cx: &mut Cx,
    symbol: &Symbol,
    input: Input,
    read_policy: ReadPolicy,
    limits: DecodeLimits,
) -> Result<Datum>

Decode input to a Datum under explicit DecodeLimits, failing if the decoded Expr is not inert data.