//! Filesystem utilities//!//! These are will be parallel if the `parallel` feature is enabled, at the expense of compiling additional dependencies//! along with runtime costs for maintaining a global [`rayon`](https://docs.rs/rayon) thread pool.//!//! For information on how to use the [`WalkDir`] type, have a look at//! * [`jwalk::WalkDir`](https://docs.rs/jwalk/0.5.1/jwalk/type.WalkDir.html) if `parallel` feature is enabled//! * [walkdir::WalkDir](https://docs.rs/walkdir/2.3.1/walkdir/struct.WalkDir.html) otherwise#[cfg(feature = "fs-walkdir-parallel")]///pub mod walkdir {    use std::path::Path;     pub use jwalk::{DirEntry as DirEntryGeneric, DirEntryIter as DirEntryIterGeneric, Error, WalkDir};     /// An alias for an uncustomized directory entry to match the one of the non-parallel version offered by `walkdir`.    pub type DirEntry = DirEntryGeneric<((), ())>;     /// Instantiate a new directory iterator which will not skip hidden files.    pub fn walkdir_new(root: impl AsRef<Path>) -> WalkDir {        WalkDir::new(root)            .skip_hidden(false)            .parallelism(jwalk::Parallelism::Serial)    }     /// Instantiate a new directory iterator which will not skip hidden files and is sorted    pub fn walkdir_sorted_new(root: impl AsRef<Path>) -> WalkDir {        WalkDir::new(root)            .skip_hidden(false)            .sort(true)            .parallelism(jwalk::Parallelism::Serial)    }     /// The Iterator yielding directory items    pub type DirEntryIter = DirEntryIterGeneric<((), ())>;} #[cfg(all(feature = "walkdir", not(feature = "fs-walkdir-parallel")))]///pub mod walkdir {    use std::path::Path;     pub use walkdir::{DirEntry, Error, WalkDir};     /// Instantiate a new directory iterator which will not skip hidden files.    pub fn walkdir_new(root: impl AsRef<Path>) -> WalkDir {        WalkDir::new(root)    }     /// Instantiate a new directory iterator which will not skip hidden files and is sorted    pub fn walkdir_sorted_new(root: impl AsRef<Path>) -> WalkDir {        WalkDir::new(root).sort_by_file_name()    }     /// The Iterator yielding directory items    pub type DirEntryIter = walkdir::IntoIter;} #[cfg(any(feature = "walkdir", feature = "fs-walkdir-parallel"))]pub use self::walkdir::{walkdir_new, walkdir_sorted_new, WalkDir}; /// Prepare open options which won't follow symlinks when the file is opened.////// Note: only effective on unix currently.pub fn open_options_no_follow() -> std::fs::OpenOptions {    #[cfg_attr(not(unix), allow(unused_mut))]    let mut options = std::fs::OpenOptions::new();    #[cfg(unix)]    {        /// Make sure that it's impossible to follow through to the target of symlinks.        /// Note that this will still follow symlinks in the path, which is what we assume        /// has been checked separately.        use std::os::unix::fs::OpenOptionsExt;        options.custom_flags(libc::O_NOFOLLOW);    }    options} mod snapshot {    use std::ops::Deref;     use crate::threading::{get_mut, get_ref, MutableOnDemand, OwnShared};     /// A structure holding enough information to reload a value if its on-disk representation changes as determined by its modified time.    #[derive(Debug)]    pub struct Snapshot<T: std::fmt::Debug> {        value: T,        modified: std::time::SystemTime,    }     /// A snapshot of a resource which is up-to-date in the moment it is retrieved.    pub type SharedSnapshot<T> = OwnShared<Snapshot<T>>;     /// Use this type for fields in structs that are to store the [`Snapshot`], typically behind an [`OwnShared`].    ///    /// Note that the resource itself is behind another [`OwnShared`] to allow it to be used without holding any kind of lock, hence    /// without blocking updates while it is used.    #[derive(Debug, Default)]    pub struct MutableSnapshot<T: std::fmt::Debug>(pub MutableOnDemand<Option<SharedSnapshot<T>>>);     impl<T: std::fmt::Debug> Deref for Snapshot<T> {        type Target = T;         fn deref(&self) -> &Self::Target {            &self.value        }    }     impl<T: std::fmt::Debug> Deref for MutableSnapshot<T> {        type Target = MutableOnDemand<Option<SharedSnapshot<T>>>;         fn deref(&self) -> &Self::Target {            &self.0        }    }     impl<T: std::fmt::Debug> MutableSnapshot<T> {        /// Create a new instance of this type.        ///        /// Useful in case `Default::default()` isn't working for some reason.        pub fn new() -> Self {            MutableSnapshot(MutableOnDemand::new(None))        }         /// Refresh `state` forcefully by re-`open`ing the resource. Note that `open()` returns `None` if the resource isn't        /// present on disk, and that it's critical that the modified time is obtained _before_ opening the resource.        pub fn force_refresh<E>(            &self,            open: impl FnOnce() -> Result<Option<(std::time::SystemTime, T)>, E>,        ) -> Result<(), E> {            let mut state = get_mut(&self.0);            *state = open()?.map(|(modified, value)| OwnShared::new(Snapshot { value, modified }));            Ok(())        }         /// Assure that the resource in `state` is up-to-date by comparing the `current_modification_time` with the one we know in `state`        /// and by acting accordingly.        /// Returns the potentially updated/reloaded resource if it is still present on disk, which then represents a snapshot that is up-to-date        /// in that very moment, or `None` if the underlying file doesn't exist.        ///        /// Note that even though this is racy, each time a request is made there is a chance to see the actual state.        pub fn recent_snapshot<E>(            &self,            mut current_modification_time: impl FnMut() -> Option<std::time::SystemTime>,            open: impl FnOnce() -> Result<Option<T>, E>,        ) -> Result<Option<SharedSnapshot<T>>, E> {            let state = get_ref(self);            let recent_modification = current_modification_time();            let buffer = match (&*state, recent_modification) {                (None, None) => (*state).clone(),                (Some(_), None) => {                    drop(state);                    let mut state = get_mut(self);                    *state = None;                    (*state).clone()                }                (Some(snapshot), Some(modified_time)) => {                    if snapshot.modified < modified_time {                        drop(state);                        let mut state = get_mut(self);                         if let (Some(_snapshot), Some(modified_time)) = (&*state, current_modification_time()) {                            *state = open()?.map(|value| {                                OwnShared::new(Snapshot {                                    value,                                    modified: modified_time,                                })                            });                        }                         (*state).clone()                    } else {                        // Note that this relies on sub-section precision or else is a race when the packed file was just changed.                        // It's nothing we can know though, so… up to the caller unfortunately.                        Some(snapshot.clone())                    }                }                (None, Some(_modified_time)) => {                    drop(state);                    let mut state = get_mut(self);                    // Still in the same situation? If so, load the buffer. This compensates for the trampling herd                    // during lazy-loading at the expense of another mtime check.                    if let (None, Some(modified_time)) = (&*state, current_modification_time()) {                        *state = open()?.map(|value| {                            OwnShared::new(Snapshot {                                value,                                modified: modified_time,                            })                        });                    }                    (*state).clone()                }            };            Ok(buffer)        }    }}pub use snapshot::{MutableSnapshot, SharedSnapshot, Snapshot};