rust/hg-core/src/vfs.rs

rust: bump to memmap2 0.5.3, micro-timer 0.4.0, and crossbeam-channel 0.5.0

The merge in 12adf8c695ed had conflicts in rust/Cargo.lock and
rust/hg-core/Cargo.toml . Let's ignore rust/Cargo.lock - it is regenerated.

For rust/hg-core/Cargo.toml, stable had dd6b67d5c256 "rust: fix unsound
`OwningDirstateMap`" which introduced ouroboros (and dropped
stable_deref_trait).

Default had ec8d9b5a5e7c "rust-hg-core: upgrade dependencies" which had a lot
of churn bumping minimum versions - also patch versions. It is indeed a good
idea to bump to *allow* use of latest package. That means that major versions
should be bumped for packages after 1.0, and for packages below 1.0 minor
versions should be bumped too. But it doesn't work to try enforce a policy of
using latest patch by bumping versions at arbitrary times.

For good or bad, the merge doesn't seem to have resolved the conflicts
correctly, and many of the minor "upgrade dependencies" were lost again.

Unfortunately, it also lost the bump of memmap2 to 0.5.3, which is needed for
Fedora packaging where 0.4 isn't available. Same with micro-timer bump to 0.4
(which already is used in rhg). crossbeam-channel bump was also lost.

This change fixes that regression by redoing these "important" lines of the
merge "correctly".

I propose this for stable, even though dependency changes on stable branches
are annoying.

use crate::errors::{HgError, IoErrorContext, IoResultExt};
use memmap2::{Mmap, MmapOptions};
use std::io::{ErrorKind, Write};
use std::path::{Path, PathBuf};

/// Filesystem access abstraction for the contents of a given "base" diretory
#[derive(Clone, Copy)]
pub struct Vfs<'a> {
    pub(crate) base: &'a Path,
}

struct FileNotFound(std::io::Error, PathBuf);

impl Vfs<'_> {
    pub fn join(&self, relative_path: impl AsRef<Path>) -> PathBuf {
        self.base.join(relative_path)
    }

    pub fn symlink_metadata(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<std::fs::Metadata, HgError> {
        let path = self.join(relative_path);
        std::fs::symlink_metadata(&path).when_reading_file(&path)
    }

    pub fn read_link(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<PathBuf, HgError> {
        let path = self.join(relative_path);
        std::fs::read_link(&path).when_reading_file(&path)
    }

    pub fn read(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<Vec<u8>, HgError> {
        let path = self.join(relative_path);
        std::fs::read(&path).when_reading_file(&path)
    }

    fn mmap_open_gen(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<Result<Mmap, FileNotFound>, HgError> {
        let path = self.join(relative_path);
        let file = match std::fs::File::open(&path) {
            Err(err) => {
                if let ErrorKind::NotFound = err.kind() {
                    return Ok(Err(FileNotFound(err, path)));
                };
                return (Err(err)).when_reading_file(&path);
            }
            Ok(file) => file,
        };
        // TODO: what are the safety requirements here?
        let mmap = unsafe { MmapOptions::new().map(&file) }
            .when_reading_file(&path)?;
        Ok(Ok(mmap))
    }

    pub fn mmap_open_opt(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<Option<Mmap>, HgError> {
        self.mmap_open_gen(relative_path).map(|res| res.ok())
    }

    pub fn mmap_open(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<Mmap, HgError> {
        match self.mmap_open_gen(relative_path)? {
            Err(FileNotFound(err, path)) => Err(err).when_reading_file(&path),
            Ok(res) => Ok(res),
        }
    }

    pub fn rename(
        &self,
        relative_from: impl AsRef<Path>,
        relative_to: impl AsRef<Path>,
    ) -> Result<(), HgError> {
        let from = self.join(relative_from);
        let to = self.join(relative_to);
        std::fs::rename(&from, &to)
            .with_context(|| IoErrorContext::RenamingFile { from, to })
    }

    pub fn remove_file(
        &self,
        relative_path: impl AsRef<Path>,
    ) -> Result<(), HgError> {
        let path = self.join(relative_path);
        std::fs::remove_file(&path)
            .with_context(|| IoErrorContext::RemovingFile(path))
    }

    #[cfg(unix)]
    pub fn create_symlink(
        &self,
        relative_link_path: impl AsRef<Path>,
        target_path: impl AsRef<Path>,
    ) -> Result<(), HgError> {
        let link_path = self.join(relative_link_path);
        std::os::unix::fs::symlink(target_path, &link_path)
            .when_writing_file(&link_path)
    }

    /// Write `contents` into a temporary file, then rename to `relative_path`.
    /// This makes writing to a file "atomic": a reader opening that path will
    /// see either the previous contents of the file or the complete new
    /// content, never a partial write.
    pub fn atomic_write(
        &self,
        relative_path: impl AsRef<Path>,
        contents: &[u8],
    ) -> Result<(), HgError> {
        let mut tmp = tempfile::NamedTempFile::new_in(self.base)
            .when_writing_file(self.base)?;
        tmp.write_all(contents)
            .and_then(|()| tmp.flush())
            .when_writing_file(tmp.path())?;
        let path = self.join(relative_path);
        tmp.persist(&path)
            .map_err(|e| e.error)
            .when_writing_file(&path)?;
        Ok(())
    }
}

fn fs_metadata(
    path: impl AsRef<Path>,
) -> Result<Option<std::fs::Metadata>, HgError> {
    let path = path.as_ref();
    match std::fs::metadata(path) {
        Ok(meta) => Ok(Some(meta)),
        Err(error) => match error.kind() {
            // TODO: when we require a Rust version where `NotADirectory` is
            // stable, invert this logic and return None for it and `NotFound`
            // and propagate any other error.
            ErrorKind::PermissionDenied => Err(error).with_context(|| {
                IoErrorContext::ReadingMetadata(path.to_owned())
            }),
            _ => Ok(None),
        },
    }
}

pub(crate) fn is_dir(path: impl AsRef<Path>) -> Result<bool, HgError> {
    Ok(fs_metadata(path)?.map_or(false, |meta| meta.is_dir()))
}

pub(crate) fn is_file(path: impl AsRef<Path>) -> Result<bool, HgError> {
    Ok(fs_metadata(path)?.map_or(false, |meta| meta.is_file()))
}