Function flatten_anyhow 

pub(crate) fn flatten_anyhow<T, E>(r: Result<Result<T>, E>) -> Result<T>
where
    E: Display + Debug + Send + Sync + 'static,

Flatten a nested Result<Result>, defaulting to converting the error type to an anyhow::Error. See https://doc.rust-lang.org/std/result/enum.Result.html#method.flatten