annotate rust/hg-core/src/dirstate_tree/status.rs @ 48202:0cc0c0972164

dirstate-v2: Only convert from SystemTime to Timestamp and not back

Converting from Timestamp back to SystemTime was only used for equality
comparison, but this can also be done on Timestamp values.

Differential Revision: https://phab.mercurial-scm.org/D11631

use crate::dirstate::status::IgnoreFnType;
use crate::dirstate_tree::dirstate_map::BorrowedPath;
use crate::dirstate_tree::dirstate_map::ChildNodesRef;
use crate::dirstate_tree::dirstate_map::DirstateMap;
use crate::dirstate_tree::dirstate_map::NodeData;
use crate::dirstate_tree::dirstate_map::NodeRef;
use crate::dirstate_tree::on_disk::DirstateV2ParseError;
use crate::dirstate_tree::on_disk::Timestamp;
use crate::matchers::get_ignore_function;
use crate::matchers::Matcher;
use crate::utils::files::get_bytes_from_os_string;
use crate::utils::files::get_path_from_bytes;
use crate::utils::hg_path::HgPath;
use crate::BadMatch;
use crate::DirstateStatus;
use crate::EntryState;
use crate::HgPathBuf;
use crate::PatternFileWarning;
use crate::StatusError;
use crate::StatusOptions;
use micro_timer::timed;
use rayon::prelude::*;
use sha1::{Digest, Sha1};
use std::borrow::Cow;
use std::io;
use std::path::Path;
use std::path::PathBuf;
use std::sync::Mutex;
use std::time::SystemTime;

/// Returns the status of the working directory compared to its parent
/// changeset.
///
/// This algorithm is based on traversing the filesystem tree (`fs` in function
/// and variable names) and dirstate tree at the same time. The core of this
/// traversal is the recursive `traverse_fs_directory_and_dirstate` function
/// and its use of `itertools::merge_join_by`. When reaching a path that only
/// exists in one of the two trees, depending on information requested by
/// `options` we may need to traverse the remaining subtree.
#[timed]
pub fn status<'tree, 'on_disk: 'tree>(
    dmap: &'tree mut DirstateMap<'on_disk>,
    matcher: &(dyn Matcher + Sync),
    root_dir: PathBuf,
    ignore_files: Vec<PathBuf>,
    options: StatusOptions,
) -> Result<(DirstateStatus<'on_disk>, Vec<PatternFileWarning>), StatusError> {
    let (ignore_fn, warnings, patterns_changed): (IgnoreFnType, _, _) =
        if options.list_ignored || options.list_unknown {
            let mut hasher = Sha1::new();
            let (ignore_fn, warnings) = get_ignore_function(
                ignore_files,
                &root_dir,
                &mut |pattern_bytes| hasher.update(pattern_bytes),
            )?;
            let new_hash = *hasher.finalize().as_ref();
            let changed = new_hash != dmap.ignore_patterns_hash;
            dmap.ignore_patterns_hash = new_hash;
            (ignore_fn, warnings, Some(changed))
        } else {
            (Box::new(|&_| true), vec![], None)
        };

    let common = StatusCommon {
        dmap,
        options,
        matcher,
        ignore_fn,
        outcome: Default::default(),
        ignore_patterns_have_changed: patterns_changed,
        new_cachable_directories: Default::default(),
        outated_cached_directories: Default::default(),
        filesystem_time_at_status_start: filesystem_now(&root_dir).ok(),
    };
    let is_at_repo_root = true;
    let hg_path = &BorrowedPath::OnDisk(HgPath::new(""));
    let has_ignored_ancestor = false;
    let root_cached_mtime = None;
    let root_dir_metadata = None;
    // If the path we have for the repository root is a symlink, do follow it.
    // (As opposed to symlinks within the working directory which are not
    // followed, using `std::fs::symlink_metadata`.)
    common.traverse_fs_directory_and_dirstate(
        has_ignored_ancestor,
        dmap.root.as_ref(),
        hg_path,
        &root_dir,
        root_dir_metadata,
        root_cached_mtime,
        is_at_repo_root,
    )?;
    let mut outcome = common.outcome.into_inner().unwrap();
    let new_cachable = common.new_cachable_directories.into_inner().unwrap();
    let outdated = common.outated_cached_directories.into_inner().unwrap();

    outcome.dirty = common.ignore_patterns_have_changed == Some(true)
        || !outdated.is_empty()
        || !new_cachable.is_empty();

    // Remove outdated mtimes before adding new mtimes, in case a given
    // directory is both
    for path in &outdated {
        let node = dmap.get_or_insert(path)?;
        if let NodeData::CachedDirectory { .. } = &node.data {
            node.data = NodeData::None
        }
    }
    for (path, mtime) in &new_cachable {
        let node = dmap.get_or_insert(path)?;
        match &node.data {
            NodeData::Entry(_) => {} // Don’t overwrite an entry
            NodeData::CachedDirectory { .. } | NodeData::None => {
                node.data = NodeData::CachedDirectory { mtime: *mtime }
            }
        }
    }

    Ok((outcome, warnings))
}

/// Bag of random things needed by various parts of the algorithm. Reduces the
/// number of parameters passed to functions.
struct StatusCommon<'a, 'tree, 'on_disk: 'tree> {
    dmap: &'tree DirstateMap<'on_disk>,
    options: StatusOptions,
    matcher: &'a (dyn Matcher + Sync),
    ignore_fn: IgnoreFnType<'a>,
    outcome: Mutex<DirstateStatus<'on_disk>>,
    new_cachable_directories: Mutex<Vec<(Cow<'on_disk, HgPath>, Timestamp)>>,
    outated_cached_directories: Mutex<Vec<Cow<'on_disk, HgPath>>>,

    /// Whether ignore files like `.hgignore` have changed since the previous
    /// time a `status()` call wrote their hash to the dirstate. `None` means
    /// we don’t know as this run doesn’t list either ignored or uknown files
    /// and therefore isn’t reading `.hgignore`.
    ignore_patterns_have_changed: Option<bool>,

    /// The current time at the start of the `status()` algorithm, as measured
    /// and possibly truncated by the filesystem.
    filesystem_time_at_status_start: Option<SystemTime>,
}

impl<'a, 'tree, 'on_disk> StatusCommon<'a, 'tree, 'on_disk> {
    fn read_dir(
        &self,
        hg_path: &HgPath,
        fs_path: &Path,
        is_at_repo_root: bool,
    ) -> Result<Vec<DirEntry>, ()> {
        DirEntry::read_dir(fs_path, is_at_repo_root)
            .map_err(|error| self.io_error(error, hg_path))
    }

    fn io_error(&self, error: std::io::Error, hg_path: &HgPath) {
        let errno = error.raw_os_error().expect("expected real OS error");
        self.outcome
            .lock()
            .unwrap()
            .bad
            .push((hg_path.to_owned().into(), BadMatch::OsError(errno)))
    }

    fn check_for_outdated_directory_cache(
        &self,
        dirstate_node: &NodeRef<'tree, 'on_disk>,
    ) -> Result<(), DirstateV2ParseError> {
        if self.ignore_patterns_have_changed == Some(true)
            && dirstate_node.cached_directory_mtime().is_some()
        {
            self.outated_cached_directories.lock().unwrap().push(
                dirstate_node
                    .full_path_borrowed(self.dmap.on_disk)?
                    .detach_from_tree(),
            )
        }
        Ok(())
    }

    /// If this returns true, we can get accurate results by only using
    /// `symlink_metadata` for child nodes that exist in the dirstate and don’t
    /// need to call `read_dir`.
    fn can_skip_fs_readdir(
        &self,
        directory_metadata: Option<&std::fs::Metadata>,
        cached_directory_mtime: Option<&Timestamp>,
    ) -> bool {
        if !self.options.list_unknown && !self.options.list_ignored {
            // All states that we care about listing have corresponding
            // dirstate entries.
            // This happens for example with `hg status -mard`.
            return true;
        }
        if !self.options.list_ignored
            && self.ignore_patterns_have_changed == Some(false)
        {
            if let Some(cached_mtime) = cached_directory_mtime {
                // The dirstate contains a cached mtime for this directory, set
                // by a previous run of the `status` algorithm which found this
                // directory eligible for `read_dir` caching.
                if let Some(meta) = directory_metadata {
                    if let Ok(current_mtime) = meta.modified() {
                        let current_mtime = Timestamp::from(current_mtime);
                        if current_mtime == *cached_mtime {
                            // The mtime of that directory has not changed
                            // since then, which means that the results of
                            // `read_dir` should also be unchanged.
                            return true;
                        }
                    }
                }
            }
        }
        false
    }

    /// Returns whether all child entries of the filesystem directory have a
    /// corresponding dirstate node or are ignored.
    fn traverse_fs_directory_and_dirstate(
        &self,
        has_ignored_ancestor: bool,
        dirstate_nodes: ChildNodesRef<'tree, 'on_disk>,
        directory_hg_path: &BorrowedPath<'tree, 'on_disk>,
        directory_fs_path: &Path,
        directory_metadata: Option<&std::fs::Metadata>,
        cached_directory_mtime: Option<&Timestamp>,
        is_at_repo_root: bool,
    ) -> Result<bool, DirstateV2ParseError> {
        if self.can_skip_fs_readdir(directory_metadata, cached_directory_mtime)
        {
            dirstate_nodes
                .par_iter()
                .map(|dirstate_node| {
                    let fs_path = directory_fs_path.join(get_path_from_bytes(
                        dirstate_node.base_name(self.dmap.on_disk)?.as_bytes(),
                    ));
                    match std::fs::symlink_metadata(&fs_path) {
                        Ok(fs_metadata) => self.traverse_fs_and_dirstate(
                            &fs_path,
                            &fs_metadata,
                            dirstate_node,
                            has_ignored_ancestor,
                        ),
                        Err(e) if e.kind() == std::io::ErrorKind::NotFound => {
                            self.traverse_dirstate_only(dirstate_node)
                        }
                        Err(error) => {
                            let hg_path =
                                dirstate_node.full_path(self.dmap.on_disk)?;
                            Ok(self.io_error(error, hg_path))
                        }
                    }
                })
                .collect::<Result<_, _>>()?;

            // We don’t know, so conservatively say this isn’t the case
            let children_all_have_dirstate_node_or_are_ignored = false;

            return Ok(children_all_have_dirstate_node_or_are_ignored);
        }

        let mut fs_entries = if let Ok(entries) = self.read_dir(
            directory_hg_path,
            directory_fs_path,
            is_at_repo_root,
        ) {
            entries
        } else {
            // Treat an unreadable directory (typically because of insufficient
            // permissions) like an empty directory. `self.read_dir` has
            // already called `self.io_error` so a warning will be emitted.
            Vec::new()
        };

        // `merge_join_by` requires both its input iterators to be sorted:

        let dirstate_nodes = dirstate_nodes.sorted();
        // `sort_unstable_by_key` doesn’t allow keys borrowing from the value:
        // https://github.com/rust-lang/rust/issues/34162
        fs_entries.sort_unstable_by(|e1, e2| e1.base_name.cmp(&e2.base_name));

        // Propagate here any error that would happen inside the comparison
        // callback below
        for dirstate_node in &dirstate_nodes {
            dirstate_node.base_name(self.dmap.on_disk)?;
        }
        itertools::merge_join_by(
            dirstate_nodes,
            &fs_entries,
            |dirstate_node, fs_entry| {
                // This `unwrap` never panics because we already propagated
                // those errors above
                dirstate_node
                    .base_name(self.dmap.on_disk)
                    .unwrap()
                    .cmp(&fs_entry.base_name)
            },
        )
        .par_bridge()
        .map(|pair| {
            use itertools::EitherOrBoth::*;
            let has_dirstate_node_or_is_ignored;
            match pair {
                Both(dirstate_node, fs_entry) => {
                    self.traverse_fs_and_dirstate(
                        &fs_entry.full_path,
                        &fs_entry.metadata,
                        dirstate_node,
                        has_ignored_ancestor,
                    )?;
                    has_dirstate_node_or_is_ignored = true
                }
                Left(dirstate_node) => {
                    self.traverse_dirstate_only(dirstate_node)?;
                    has_dirstate_node_or_is_ignored = true;
                }
                Right(fs_entry) => {
                    has_dirstate_node_or_is_ignored = self.traverse_fs_only(
                        has_ignored_ancestor,
                        directory_hg_path,
                        fs_entry,
                    )
                }
            }
            Ok(has_dirstate_node_or_is_ignored)
        })
        .try_reduce(|| true, |a, b| Ok(a && b))
    }

    fn traverse_fs_and_dirstate(
        &self,
        fs_path: &Path,
        fs_metadata: &std::fs::Metadata,
        dirstate_node: NodeRef<'tree, 'on_disk>,
        has_ignored_ancestor: bool,
    ) -> Result<(), DirstateV2ParseError> {
        self.check_for_outdated_directory_cache(&dirstate_node)?;
        let hg_path = &dirstate_node.full_path_borrowed(self.dmap.on_disk)?;
        let file_type = fs_metadata.file_type();
        let file_or_symlink = file_type.is_file() || file_type.is_symlink();
        if !file_or_symlink {
            // If we previously had a file here, it was removed (with
            // `hg rm` or similar) or deleted before it could be
            // replaced by a directory or something else.
            self.mark_removed_or_deleted_if_file(
                &hg_path,
                dirstate_node.state()?,
            );
        }
        if file_type.is_dir() {
            if self.options.collect_traversed_dirs {
                self.outcome
                    .lock()
                    .unwrap()
                    .traversed
                    .push(hg_path.detach_from_tree())
            }
            let is_ignored = has_ignored_ancestor || (self.ignore_fn)(hg_path);
            let is_at_repo_root = false;
            let children_all_have_dirstate_node_or_are_ignored = self
                .traverse_fs_directory_and_dirstate(
                    is_ignored,
                    dirstate_node.children(self.dmap.on_disk)?,
                    hg_path,
                    fs_path,
                    Some(fs_metadata),
                    dirstate_node.cached_directory_mtime(),
                    is_at_repo_root,
                )?;
            self.maybe_save_directory_mtime(
                children_all_have_dirstate_node_or_are_ignored,
                fs_metadata,
                dirstate_node,
            )?
        } else {
            if file_or_symlink && self.matcher.matches(hg_path) {
                if let Some(state) = dirstate_node.state()? {
                    match state {
                        EntryState::Added => self
                            .outcome
                            .lock()
                            .unwrap()
                            .added
                            .push(hg_path.detach_from_tree()),
                        EntryState::Removed => self
                            .outcome
                            .lock()
                            .unwrap()
                            .removed
                            .push(hg_path.detach_from_tree()),
                        EntryState::Merged => self
                            .outcome
                            .lock()
                            .unwrap()
                            .modified
                            .push(hg_path.detach_from_tree()),
                        EntryState::Normal => self
                            .handle_normal_file(&dirstate_node, fs_metadata)?,
                    }
                } else {
                    // `node.entry.is_none()` indicates a "directory"
                    // node, but the filesystem has a file
                    self.mark_unknown_or_ignored(
                        has_ignored_ancestor,
                        hg_path,
                    );
                }
            }

            for child_node in dirstate_node.children(self.dmap.on_disk)?.iter()
            {
                self.traverse_dirstate_only(child_node)?
            }
        }
        Ok(())
    }

    fn maybe_save_directory_mtime(
        &self,
        children_all_have_dirstate_node_or_are_ignored: bool,
        directory_metadata: &std::fs::Metadata,
        dirstate_node: NodeRef<'tree, 'on_disk>,
    ) -> Result<(), DirstateV2ParseError> {
        if children_all_have_dirstate_node_or_are_ignored {
            // All filesystem directory entries from `read_dir` have a
            // corresponding node in the dirstate, so we can reconstitute the
            // names of those entries without calling `read_dir` again.
            if let (Some(status_start), Ok(directory_mtime)) = (
                &self.filesystem_time_at_status_start,
                directory_metadata.modified(),
            ) {
                // Although the Rust standard library’s `SystemTime` type
                // has nanosecond precision, the times reported for a
                // directory’s (or file’s) modified time may have lower
                // resolution based on the filesystem (for example ext3
                // only stores integer seconds), kernel (see
                // https://stackoverflow.com/a/14393315/1162888), etc.
                if &directory_mtime >= status_start {
                    // The directory was modified too recently, don’t cache its
                    // `read_dir` results.
                    //
                    // A timeline like this is possible:
                    //
                    // 1. A change to this directory (direct child was
                    //    added or removed) cause its mtime to be set
                    //    (possibly truncated) to `directory_mtime`
                    // 2. This `status` algorithm calls `read_dir`
                    // 3. An other change is made to the same directory is
                    //    made so that calling `read_dir` agin would give
                    //    different results, but soon enough after 1. that
                    //    the mtime stays the same
                    //
                    // On a system where the time resolution poor, this
                    // scenario is not unlikely if all three steps are caused
                    // by the same script.
                } else {
                    // We’ve observed (through `status_start`) that time has
                    // “progressed” since `directory_mtime`, so any further
                    // change to this directory is extremely likely to cause a
                    // different mtime.
                    //
                    // Having the same mtime again is not entirely impossible
                    // since the system clock is not monotonous. It could jump
                    // backward to some point before `directory_mtime`, then a
                    // directory change could potentially happen during exactly
                    // the wrong tick.
                    //
                    // We deem this scenario (unlike the previous one) to be
                    // unlikely enough in practice.
                    let timestamp = directory_mtime.into();
                    let cached = dirstate_node.cached_directory_mtime();
                    if cached != Some(&timestamp) {
                        let hg_path = dirstate_node
                            .full_path_borrowed(self.dmap.on_disk)?
                            .detach_from_tree();
                        self.new_cachable_directories
                            .lock()
                            .unwrap()
                            .push((hg_path, timestamp))
                    }
                }
            }
        }
        Ok(())
    }

    /// A file with `EntryState::Normal` in the dirstate was found in the
    /// filesystem
    fn handle_normal_file(
        &self,
        dirstate_node: &NodeRef<'tree, 'on_disk>,
        fs_metadata: &std::fs::Metadata,
    ) -> Result<(), DirstateV2ParseError> {
        // Keep the low 31 bits
        fn truncate_u64(value: u64) -> i32 {
            (value & 0x7FFF_FFFF) as i32
        }
        fn truncate_i64(value: i64) -> i32 {
            (value & 0x7FFF_FFFF) as i32
        }

        let entry = dirstate_node
            .entry()?
            .expect("handle_normal_file called with entry-less node");
        let hg_path = &dirstate_node.full_path_borrowed(self.dmap.on_disk)?;
        let mode_changed =
            || self.options.check_exec && entry.mode_changed(fs_metadata);
        let size = entry.size();
        let size_changed = size != truncate_u64(fs_metadata.len());
        if size >= 0 && size_changed && fs_metadata.file_type().is_symlink() {
            // issue6456: Size returned may be longer due to encryption
            // on EXT-4 fscrypt. TODO maybe only do it on EXT4?
            self.outcome
                .lock()
                .unwrap()
                .unsure
                .push(hg_path.detach_from_tree())
        } else if dirstate_node.has_copy_source()
            || entry.is_from_other_parent()
            || (size >= 0 && (size_changed || mode_changed()))
        {
            self.outcome
                .lock()
                .unwrap()
                .modified
                .push(hg_path.detach_from_tree())
        } else {
            let mtime = mtime_seconds(fs_metadata);
            if truncate_i64(mtime) != entry.mtime()
                || mtime == self.options.last_normal_time
            {
                self.outcome
                    .lock()
                    .unwrap()
                    .unsure
                    .push(hg_path.detach_from_tree())
            } else if self.options.list_clean {
                self.outcome
                    .lock()
                    .unwrap()
                    .clean
                    .push(hg_path.detach_from_tree())
            }
        }
        Ok(())
    }

    /// A node in the dirstate tree has no corresponding filesystem entry
    fn traverse_dirstate_only(
        &self,
        dirstate_node: NodeRef<'tree, 'on_disk>,
    ) -> Result<(), DirstateV2ParseError> {
        self.check_for_outdated_directory_cache(&dirstate_node)?;
        self.mark_removed_or_deleted_if_file(
            &dirstate_node.full_path_borrowed(self.dmap.on_disk)?,
            dirstate_node.state()?,
        );
        dirstate_node
            .children(self.dmap.on_disk)?
            .par_iter()
            .map(|child_node| self.traverse_dirstate_only(child_node))
            .collect()
    }

    /// A node in the dirstate tree has no corresponding *file* on the
    /// filesystem
    ///
    /// Does nothing on a "directory" node
    fn mark_removed_or_deleted_if_file(
        &self,
        hg_path: &BorrowedPath<'tree, 'on_disk>,
        dirstate_node_state: Option<EntryState>,
    ) {
        if let Some(state) = dirstate_node_state {
            if self.matcher.matches(hg_path) {
                if let EntryState::Removed = state {
                    self.outcome
                        .lock()
                        .unwrap()
                        .removed
                        .push(hg_path.detach_from_tree())
                } else {
                    self.outcome
                        .lock()
                        .unwrap()
                        .deleted
                        .push(hg_path.detach_from_tree())
                }
            }
        }
    }

    /// Something in the filesystem has no corresponding dirstate node
    ///
    /// Returns whether that path is ignored
    fn traverse_fs_only(
        &self,
        has_ignored_ancestor: bool,
        directory_hg_path: &HgPath,
        fs_entry: &DirEntry,
    ) -> bool {
        let hg_path = directory_hg_path.join(&fs_entry.base_name);
        let file_type = fs_entry.metadata.file_type();
        let file_or_symlink = file_type.is_file() || file_type.is_symlink();
        if file_type.is_dir() {
            let is_ignored =
                has_ignored_ancestor || (self.ignore_fn)(&hg_path);
            let traverse_children = if is_ignored {
                // Descendants of an ignored directory are all ignored
                self.options.list_ignored
            } else {
                // Descendants of an unknown directory may be either unknown or
                // ignored
                self.options.list_unknown || self.options.list_ignored
            };
            if traverse_children {
                let is_at_repo_root = false;
                if let Ok(children_fs_entries) = self.read_dir(
                    &hg_path,
                    &fs_entry.full_path,
                    is_at_repo_root,
                ) {
                    children_fs_entries.par_iter().for_each(|child_fs_entry| {
                        self.traverse_fs_only(
                            is_ignored,
                            &hg_path,
                            child_fs_entry,
                        );
                    })
                }
            }
            if self.options.collect_traversed_dirs {
                self.outcome.lock().unwrap().traversed.push(hg_path.into())
            }
            is_ignored
        } else {
            if file_or_symlink {
                if self.matcher.matches(&hg_path) {
                    self.mark_unknown_or_ignored(
                        has_ignored_ancestor,
                        &BorrowedPath::InMemory(&hg_path),
                    )
                } else {
                    // We haven’t computed whether this path is ignored. It
                    // might not be, and a future run of status might have a
                    // different matcher that matches it. So treat it as not
                    // ignored. That is, inhibit readdir caching of the parent
                    // directory.
                    false
                }
            } else {
                // This is neither a directory, a plain file, or a symlink.
                // Treat it like an ignored file.
                true
            }
        }
    }

    /// Returns whether that path is ignored
    fn mark_unknown_or_ignored(
        &self,
        has_ignored_ancestor: bool,
        hg_path: &BorrowedPath<'_, 'on_disk>,
    ) -> bool {
        let is_ignored = has_ignored_ancestor || (self.ignore_fn)(&hg_path);
        if is_ignored {
            if self.options.list_ignored {
                self.outcome
                    .lock()
                    .unwrap()
                    .ignored
                    .push(hg_path.detach_from_tree())
            }
        } else {
            if self.options.list_unknown {
                self.outcome
                    .lock()
                    .unwrap()
                    .unknown
                    .push(hg_path.detach_from_tree())
            }
        }
        is_ignored
    }
}

#[cfg(unix)] // TODO
fn mtime_seconds(metadata: &std::fs::Metadata) -> i64 {
    // Going through `Metadata::modified()` would be portable, but would take
    // care to construct a `SystemTime` value with sub-second precision just
    // for us to throw that away here.
    use std::os::unix::fs::MetadataExt;
    metadata.mtime()
}

struct DirEntry {
    base_name: HgPathBuf,
    full_path: PathBuf,
    metadata: std::fs::Metadata,
}

impl DirEntry {
    /// Returns **unsorted** entries in the given directory, with name and
    /// metadata.
    ///
    /// If a `.hg` sub-directory is encountered:
    ///
    /// * At the repository root, ignore that sub-directory
    /// * Elsewhere, we’re listing the content of a sub-repo. Return an empty
    ///   list instead.
    fn read_dir(path: &Path, is_at_repo_root: bool) -> io::Result<Vec<Self>> {
        let mut results = Vec::new();
        for entry in path.read_dir()? {
            let entry = entry?;
            let metadata = entry.metadata()?;
            let name = get_bytes_from_os_string(entry.file_name());
            // FIXME don't do this when cached
            if name == b".hg" {
                if is_at_repo_root {
                    // Skip the repo’s own .hg (might be a symlink)
                    continue;
                } else if metadata.is_dir() {
                    // A .hg sub-directory at another location means a subrepo,
                    // skip it entirely.
                    return Ok(Vec::new());
                }
            }
            results.push(DirEntry {
                base_name: name.into(),
                full_path: entry.path(),
                metadata,
            })
        }
        Ok(results)
    }
}

/// Return the `mtime` of a temporary file newly-created in the `.hg` directory
/// of the give repository.
///
/// This is similar to `SystemTime::now()`, with the result truncated to the
/// same time resolution as other files’ modification times. Using `.hg`
/// instead of the system’s default temporary directory (such as `/tmp`) makes
/// it more likely the temporary file is in the same disk partition as contents
/// of the working directory, which can matter since different filesystems may
/// store timestamps with different resolutions.
///
/// This may fail, typically if we lack write permissions. In that case we
/// should continue the `status()` algoritm anyway and consider the current
/// date/time to be unknown.
fn filesystem_now(repo_root: &Path) -> Result<SystemTime, io::Error> {
    tempfile::tempfile_in(repo_root.join(".hg"))?
        .metadata()?
        .modified()
}