use crate::{compound, loose, pack};use std::path::PathBuf; /// Returned by [`compound::Db::at()`]#[derive(thiserror::Error, Debug)]#[allow(missing_docs)]pub enum Error {    #[error("The objects directory at '{0}' is not an accessible directory")]    Inaccessible(PathBuf),    #[error(transparent)]    Pack(#[from] pack::bundle::Error),    #[error(transparent)]    Alternate(#[from] Box<crate::alternate::Error>),} /// Instantiationimpl compound::Db {    /// Returns a compound database as initialized from the given git `objects_directory`.    pub fn at(objects_directory: impl Into<PathBuf>) -> Result<compound::Db, Error> {        let loose_objects = objects_directory.into();        if !loose_objects.is_dir() {            return Err(Error::Inaccessible(loose_objects));        }        let packs = match std::fs::read_dir(loose_objects.join("pack")) {            Ok(entries) => {                let mut packs_and_sizes = entries                    .filter_map(Result::ok)                    .filter_map(|e| e.metadata().map(|md| (e.path(), md)).ok())                    .filter(|(_, md)| md.file_type().is_file())                    .filter(|(p, _)| {                        p.extension().unwrap_or_default() == "idx"                            && p.file_name().unwrap_or_default().to_string_lossy().starts_with("pack-")                    })                    .map(|(p, md)| pack::Bundle::at(p).map(|b| (b, md.len())))                    .collect::<Result<Vec<_>, _>>()?;                packs_and_sizes.sort_by_key(|e| e.1);                packs_and_sizes.into_iter().rev().map(|(b, _)| b).collect()            }            Err(_) => Vec::new(),        };         Ok(compound::Db {            loose: loose::Db::at(loose_objects.clone()),            packs,            alternates: crate::alternate::resolve(loose_objects).map_err(Box::new)?,        })    }}