// Licensed to the Apache Software Foundation (ASF) under one
// or more contributor license agreements.  See the NOTICE file
// distributed with this work for additional information
// regarding copyright ownership.  The ASF licenses this file
// to you under the Apache License, Version 2.0 (the
// "License"); you may not use this file except in compliance
// with the License.  You may obtain a copy of the License at
//
//   http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing,
// software distributed under the License is distributed on an
// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
// KIND, either express or implied.  See the License for the
// specific language governing permissions and limitations
// under the License..

//! Filesystem manipulation operations.

#![deny(unsafe_op_in_unsafe_fn)]
use crate::ffi::OsString;
use crate::fmt;
use crate::io::{self, Initializer, IoSlice, IoSliceMut, Read, Seek, SeekFrom, Write};
use crate::path::{Path, PathBuf};
use crate::sys::fs as fs_imp;
use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};
use crate::time::SystemTime;
#[cfg(not(feature = "untrusted_fs"))]
use crate::untrusted::path::PathEx;

/// A reference to an open file on the filesystem.
///
/// An instance of a `File` can be read and/or written depending on what options
/// it was opened with. Files also implement [`Seek`] to alter the logical cursor
/// that the file contains internally.
///
/// Files are automatically closed when they go out of scope.  Errors detected
/// on closing are ignored by the implementation of `Drop`.  Use the method
/// [`sync_all`] if these errors must be manually handled.
///
/// # Examples
///
/// Creates a new file and write bytes to it (you can also use [`write()`]):
///
/// ```no_run
/// use std::fs::File;
/// use std::io::prelude::*;
///
/// fn main() -> std::io::Result<()> {
///     let mut file = File::create("foo.txt")?;
///     file.write_all(b"Hello, world!")?;
///     Ok(())
/// }
/// ```
///
/// Read the contents of a file into a [`String`] (you can also use [`read`]):
///
/// ```no_run
/// use std::fs::File;
/// use std::io::prelude::*;
///
/// fn main() -> std::io::Result<()> {
///     let mut file = File::open("foo.txt")?;
///     let mut contents = String::new();
///     file.read_to_string(&mut contents)?;
///     assert_eq!(contents, "Hello, world!");
///     Ok(())
/// }
/// ```
///
/// It can be more efficient to read the contents of a file with a buffered
/// [`Read`]er. This can be accomplished with [`BufReader<R>`]:
///
/// ```no_run
/// use std::fs::File;
/// use std::io::BufReader;
/// use std::io::prelude::*;
///
/// fn main() -> std::io::Result<()> {
///     let file = File::open("foo.txt")?;
///     let mut buf_reader = BufReader::new(file);
///     let mut contents = String::new();
///     buf_reader.read_to_string(&mut contents)?;
///     assert_eq!(contents, "Hello, world!");
///     Ok(())
/// }
/// ```
///
/// Note that, although read and write methods require a `&mut File`, because
/// of the interfaces for [`Read`] and [`Write`], the holder of a `&File` can
/// still modify the file, either through methods that take `&File` or by
/// retrieving the underlying OS object and modifying the file that way.
/// Additionally, many operating systems allow concurrent modification of files
/// by different processes. Avoid assuming that holding a `&File` means that the
/// file will not change.
///
/// [`BufReader<R>`]: io::BufReader
/// [`sync_all`]: File::sync_all
pub struct File {
    inner: fs_imp::File,
}

/// Metadata information about a file.
///
/// This structure is returned from the [`metadata`] or
/// [`symlink_metadata`] function or method and represents known
/// metadata about a file such as its permissions, size, modification
/// times, etc.
#[derive(Clone)]
pub struct Metadata(fs_imp::FileAttr);

/// Iterator over the entries in a directory.
///
/// This iterator is returned from the [`read_dir`] function of this module and
/// will yield instances of [`io::Result`]`<`[`DirEntry`]`>`. Through a [`DirEntry`]
/// information like the entry's path and possibly other metadata can be
/// learned.
///
/// The order in which this iterator returns entries is platform and filesystem
/// dependent.
///
/// # Errors
///
/// This [`io::Result`] will be an [`Err`] if there's some sort of intermittent
/// IO error during iteration.
#[derive(Debug)]
pub struct ReadDir(fs_imp::ReadDir);

/// Entries returned by the [`ReadDir`] iterator.
///
/// An instance of `DirEntry` represents an entry inside of a directory on the
/// filesystem. Each entry can be inspected via methods to learn about the full
/// path or possibly other metadata through per-platform extension traits.
pub struct DirEntry(fs_imp::DirEntry);

/// Options and flags which can be used to configure how a file is opened.
///
/// This builder exposes the ability to configure how a [`File`] is opened and
/// what operations are permitted on the open file. The [`File::open`] and
/// [`File::create`] methods are aliases for commonly used options using this
/// builder.
///
/// Generally speaking, when using `OpenOptions`, you'll first call
/// [`OpenOptions::new`], then chain calls to methods to set each option, then
/// call [`OpenOptions::open`], passing the path of the file you're trying to
/// open. This will give you a [`io::Result`] with a [`File`] inside that you
/// can further operate on.
///
/// # Examples
///
/// Opening a file to read:
///
/// ```no_run
/// use std::fs::OpenOptions;
///
/// let file = OpenOptions::new().read(true).open("foo.txt");
/// ```
///
/// Opening a file for both reading and writing, as well as creating it if it
/// doesn't exist:
///
/// ```no_run
/// use std::fs::OpenOptions;
///
/// let file = OpenOptions::new()
///             .read(true)
///             .write(true)
///             .create(true)
///             .open("foo.txt");
/// ```
#[derive(Clone, Debug)]
pub struct OpenOptions(fs_imp::OpenOptions);

/// Representation of the various permissions on a file.
///
/// This module only currently provides one bit of information,
/// [`Permissions::readonly`], which is exposed on all currently supported
/// platforms. Unix-specific functionality, such as mode bits, is available
/// through the [`PermissionsExt`] trait.
///
/// [`PermissionsExt`]: crate::os::unix::fs::PermissionsExt
#[derive(Clone, PartialEq, Eq, Debug)]
pub struct Permissions(fs_imp::FilePermissions);

/// A structure representing a type of file with accessors for each file type.
/// It is returned by [`Metadata::file_type`] method.
#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
#[cfg_attr(not(test), rustc_diagnostic_item = "FileType")]
pub struct FileType(fs_imp::FileType);

/// A builder used to create directories in various manners.
///
/// This builder also supports platform-specific options.
#[cfg_attr(not(test), rustc_diagnostic_item = "DirBuilder")]
#[derive(Debug)]
pub struct DirBuilder {
    inner: fs_imp::DirBuilder,
    recursive: bool,
}

/// Indicates how large a buffer to pre-allocate before reading the entire file.
fn initial_buffer_size(file: &File) -> usize {
    // Allocate one extra byte so the buffer doesn't need to grow before the
    // final `read` call at the end of the file.  Don't worry about `usize`
    // overflow because reading will fail regardless in that case.
    file.metadata().map(|m| m.len() as usize + 1).unwrap_or(0)
}

/// Read the entire contents of a file into a bytes vector.
///
/// This is a convenience function for using [`File::open`] and [`read_to_end`]
/// with fewer imports and without an intermediate variable. It pre-allocates a
/// buffer based on the file size when available, so it is generally faster than
/// reading into a vector created with [`Vec::new()`].
///
/// [`read_to_end`]: Read::read_to_end
///
/// # Errors
///
/// This function will return an error if `path` does not already exist.
/// Other errors may also be returned according to [`OpenOptions::open`].
///
/// It will also return an error if it encounters while reading an error
/// of a kind other than [`io::ErrorKind::Interrupted`].
///
/// # Examples
///
/// ```no_run
/// use std::fs;
/// use std::net::SocketAddr;
///
/// fn main() -> Result<(), Box<dyn std::error::Error + 'static>> {
///     let foo: SocketAddr = String::from_utf8_lossy(&fs::read("address.txt")?).parse()?;
///     Ok(())
/// }
/// ```
pub fn read<P: AsRef<Path>>(path: P) -> io::Result<Vec<u8>> {
    fn inner(path: &Path) -> io::Result<Vec<u8>> {
        let mut file = File::open(path)?;
        let mut bytes = Vec::with_capacity(initial_buffer_size(&file));
        file.read_to_end(&mut bytes)?;
        Ok(bytes)
    }
    inner(path.as_ref())
}

/// Read the entire contents of a file into a string.
///
/// This is a convenience function for using [`File::open`] and [`read_to_string`]
/// with fewer imports and without an intermediate variable. It pre-allocates a
/// buffer based on the file size when available, so it is generally faster than
/// reading into a string created with [`String::new()`].
///
/// [`read_to_string`]: Read::read_to_string
///
/// # Errors
///
/// This function will return an error if `path` does not already exist.
/// Other errors may also be returned according to [`OpenOptions::open`].
///
/// It will also return an error if it encounters while reading an error
/// of a kind other than [`io::ErrorKind::Interrupted`],
/// or if the contents of the file are not valid UTF-8.
///
/// # Examples
///
/// ```no_run
/// use std::fs;
/// use std::net::SocketAddr;
/// use std::error::Error;
///
/// fn main() -> Result<(), Box<dyn Error>> {
///     let foo: SocketAddr = fs::read_to_string("address.txt")?.parse()?;
///     Ok(())
/// }
/// ```
pub fn read_to_string<P: AsRef<Path>>(path: P) -> io::Result<String> {
    fn inner(path: &Path) -> io::Result<String> {
        let mut file = File::open(path)?;
        let mut string = String::with_capacity(initial_buffer_size(&file));
        file.read_to_string(&mut string)?;
        Ok(string)
    }
    inner(path.as_ref())
}

/// Write a slice as the entire contents of a file.
///
/// This function will create a file if it does not exist,
/// and will entirely replace its contents if it does.
///
/// This is a convenience function for using [`File::create`] and [`write_all`]
/// with fewer imports.
///
/// [`write_all`]: Write::write_all
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::write("foo.txt", b"Lorem ipsum")?;
///     fs::write("bar.txt", "dolor sit")?;
///     Ok(())
/// }
/// ```
pub fn write<P: AsRef<Path>, C: AsRef<[u8]>>(path: P, contents: C) -> io::Result<()> {
    fn inner(path: &Path, contents: &[u8]) -> io::Result<()> {
        File::create(path)?.write_all(contents)
    }
    inner(path.as_ref(), contents.as_ref())
}

impl File {
    /// Attempts to open a file in read-only mode.
    ///
    /// See the [`OpenOptions::open`] method for more details.
    ///
    /// # Errors
    ///
    /// This function will return an error if `path` does not already exist.
    /// Other errors may also be returned according to [`OpenOptions::open`].
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut f = File::open("foo.txt")?;
    ///     Ok(())
    /// }
    /// ```
    pub fn open<P: AsRef<Path>>(path: P) -> io::Result<File> {
        OpenOptions::new().read(true).open(path.as_ref())
    }

    /// Opens a file in write-only mode.
    ///
    /// This function will create a file if it does not exist,
    /// and will truncate it if it does.
    ///
    /// See the [`OpenOptions::open`] function for more details.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut f = File::create("foo.txt")?;
    ///     Ok(())
    /// }
    /// ```
    pub fn create<P: AsRef<Path>>(path: P) -> io::Result<File> {
        OpenOptions::new().write(true).create(true).truncate(true).open(path.as_ref())
    }

    /// Returns a new OpenOptions object.
    ///
    /// This function returns a new OpenOptions object that you can use to
    /// open or create a file with specific options if `open()` or `create()`
    /// are not appropriate.
    ///
    /// It is equivalent to `OpenOptions::new()` but allows you to write more
    /// readable code. Instead of `OpenOptions::new().read(true).open("foo.txt")`
    /// you can write `File::with_options().read(true).open("foo.txt")`. This
    /// also avoids the need to import `OpenOptions`.
    ///
    /// See the [`OpenOptions::new`] function for more details.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// #![feature(with_options)]
    /// use std::fs::File;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut f = File::with_options().read(true).open("foo.txt")?;
    ///     Ok(())
    /// }
    /// ```
    pub fn with_options() -> OpenOptions {
        OpenOptions::new()
    }

    /// Attempts to sync all OS-internal metadata to disk.
    ///
    /// This function will attempt to ensure that all in-memory data reaches the
    /// filesystem before returning.
    ///
    /// This can be used to handle errors that would otherwise only be caught
    /// when the `File` is closed.  Dropping a file will ignore errors in
    /// synchronizing this in-memory data.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    /// use std::io::prelude::*;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut f = File::create("foo.txt")?;
    ///     f.write_all(b"Hello, world!")?;
    ///
    ///     f.sync_all()?;
    ///     Ok(())
    /// }
    /// ```
    pub fn sync_all(&self) -> io::Result<()> {
        self.inner.fsync()
    }

    /// This function is similar to [`sync_all`], except that it might not
    /// synchronize file metadata to the filesystem.
    ///
    /// This is intended for use cases that must synchronize content, but don't
    /// need the metadata on disk. The goal of this method is to reduce disk
    /// operations.
    ///
    /// Note that some platforms may simply implement this in terms of
    /// [`sync_all`].
    ///
    /// [`sync_all`]: File::sync_all
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    /// use std::io::prelude::*;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut f = File::create("foo.txt")?;
    ///     f.write_all(b"Hello, world!")?;
    ///
    ///     f.sync_data()?;
    ///     Ok(())
    /// }
    /// ```
    pub fn sync_data(&self) -> io::Result<()> {
        self.inner.datasync()
    }

    /// Truncates or extends the underlying file, updating the size of
    /// this file to become `size`.
    ///
    /// If the `size` is less than the current file's size, then the file will
    /// be shrunk. If it is greater than the current file's size, then the file
    /// will be extended to `size` and have all of the intermediate data filled
    /// in with 0s.
    ///
    /// The file's cursor isn't changed. In particular, if the cursor was at the
    /// end and the file is shrunk using this operation, the cursor will now be
    /// past the end.
    ///
    /// # Errors
    ///
    /// This function will return an error if the file is not opened for writing.
    /// Also, std::io::ErrorKind::InvalidInput will be returned if the desired
    /// length would cause an overflow due to the implementation specifics.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut f = File::create("foo.txt")?;
    ///     f.set_len(10)?;
    ///     Ok(())
    /// }
    /// ```
    ///
    /// Note that this method alters the content of the underlying file, even
    /// though it takes `&self` rather than `&mut self`.
    pub fn set_len(&self, size: u64) -> io::Result<()> {
        self.inner.truncate(size)
    }

    /// Queries metadata about the underlying file.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut f = File::open("foo.txt")?;
    ///     let metadata = f.metadata()?;
    ///     Ok(())
    /// }
    /// ```
    pub fn metadata(&self) -> io::Result<Metadata> {
        self.inner.file_attr().map(Metadata)
    }

    /// Creates a new `File` instance that shares the same underlying file handle
    /// as the existing `File` instance. Reads, writes, and seeks will affect
    /// both `File` instances simultaneously.
    ///
    /// # Examples
    ///
    /// Creates two handles for a file named `foo.txt`:
    ///
    /// ```no_run
    /// use std::fs::File;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut file = File::open("foo.txt")?;
    ///     let file_copy = file.try_clone()?;
    ///     Ok(())
    /// }
    /// ```
    ///
    /// Assuming there’s a file named `foo.txt` with contents `abcdef\n`, create
    /// two handles, seek one of them, and read the remaining bytes from the
    /// other handle:
    ///
    /// ```no_run
    /// use std::fs::File;
    /// use std::io::SeekFrom;
    /// use std::io::prelude::*;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut file = File::open("foo.txt")?;
    ///     let mut file_copy = file.try_clone()?;
    ///
    ///     file.seek(SeekFrom::Start(3))?;
    ///
    ///     let mut contents = vec![];
    ///     file_copy.read_to_end(&mut contents)?;
    ///     assert_eq!(contents, b"def\n");
    ///     Ok(())
    /// }
    /// ```
    pub fn try_clone(&self) -> io::Result<File> {
        Ok(File { inner: self.inner.duplicate()? })
    }

    /// Changes the permissions on the underlying file.
    ///
    /// # Platform-specific behavior
    ///
    /// This function currently corresponds to the `fchmod` function on Unix and
    /// the `SetFileInformationByHandle` function on Windows. Note that, this
    /// [may change in the future][changes].
    ///
    /// [changes]: io#platform-specific-behavior
    ///
    /// # Errors
    ///
    /// This function will return an error if the user lacks permission change
    /// attributes on the underlying file. It may also return an error in other
    /// os-specific unspecified cases.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// fn main() -> std::io::Result<()> {
    ///     use std::fs::File;
    ///
    ///     let file = File::open("foo.txt")?;
    ///     let mut perms = file.metadata()?.permissions();
    ///     perms.set_readonly(true);
    ///     file.set_permissions(perms)?;
    ///     Ok(())
    /// }
    /// ```
    ///
    /// Note that this method alters the permissions of the underlying file,
    /// even though it takes `&self` rather than `&mut self`.
    pub fn set_permissions(&self, perm: Permissions) -> io::Result<()> {
        self.inner.set_permissions(perm.0)
    }
}

// In addition to the `impl`s here, `File` also has `impl`s for
// `AsFd`/`From<OwnedFd>`/`Into<OwnedFd>` and
// `AsRawFd`/`IntoRawFd`/`FromRawFd`, on Unix and WASI, and
// `AsHandle`/`From<OwnedHandle>`/`Into<OwnedHandle>` and
// `AsRawHandle`/`IntoRawHandle`/`FromRawHandle` on Windows.

impl AsInner<fs_imp::File> for File {
    fn as_inner(&self) -> &fs_imp::File {
        &self.inner
    }
}
impl FromInner<fs_imp::File> for File {
    fn from_inner(f: fs_imp::File) -> File {
        File { inner: f }
    }
}
impl IntoInner<fs_imp::File> for File {
    fn into_inner(self) -> fs_imp::File {
        self.inner
    }
}

impl fmt::Debug for File {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.inner.fmt(f)
    }
}

impl Read for File {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.inner.read(buf)
    }

    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        self.inner.read_vectored(bufs)
    }

    #[inline]
    fn is_read_vectored(&self) -> bool {
        self.inner.is_read_vectored()
    }

    #[inline]
    unsafe fn initializer(&self) -> Initializer {
        // SAFETY: Read is guaranteed to work on uninitialized memory
        unsafe { Initializer::nop() }
    }
}

impl Write for File {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.inner.write(buf)
    }

    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        self.inner.write_vectored(bufs)
    }

    #[inline]
    fn is_write_vectored(&self) -> bool {
        self.inner.is_write_vectored()
    }

    fn flush(&mut self) -> io::Result<()> {
        self.inner.flush()
    }
}

impl Seek for File {
    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
        self.inner.seek(pos)
    }
}

impl Read for &File {
    fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
        self.inner.read(buf)
    }

    fn read_vectored(&mut self, bufs: &mut [IoSliceMut<'_>]) -> io::Result<usize> {
        self.inner.read_vectored(bufs)
    }

    #[inline]
    fn is_read_vectored(&self) -> bool {
        self.inner.is_read_vectored()
    }

    #[inline]
    unsafe fn initializer(&self) -> Initializer {
        // SAFETY: Read is guaranteed to work on uninitialized memory
        unsafe { Initializer::nop() }
    }
}

impl Write for &File {
    fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
        self.inner.write(buf)
    }

    fn write_vectored(&mut self, bufs: &[IoSlice<'_>]) -> io::Result<usize> {
        self.inner.write_vectored(bufs)
    }

    #[inline]
    fn is_write_vectored(&self) -> bool {
        self.inner.is_write_vectored()
    }

    fn flush(&mut self) -> io::Result<()> {
        self.inner.flush()
    }
}

impl Seek for &File {
    fn seek(&mut self, pos: SeekFrom) -> io::Result<u64> {
        self.inner.seek(pos)
    }
}

impl OpenOptions {
    /// Creates a blank new set of options ready for configuration.
    ///
    /// All options are initially set to `false`.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::OpenOptions;
    ///
    /// let mut options = OpenOptions::new();
    /// let file = options.read(true).open("foo.txt");
    /// ```
    pub fn new() -> Self {
        OpenOptions(fs_imp::OpenOptions::new())
    }

    /// Sets the option for read access.
    ///
    /// This option, when true, will indicate that the file should be
    /// `read`-able if opened.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::OpenOptions;
    ///
    /// let file = OpenOptions::new().read(true).open("foo.txt");
    /// ```
    pub fn read(&mut self, read: bool) -> &mut Self {
        self.0.read(read);
        self
    }

    /// Sets the option for write access.
    ///
    /// This option, when true, will indicate that the file should be
    /// `write`-able if opened.
    ///
    /// If the file already exists, any write calls on it will overwrite its
    /// contents, without truncating it.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::OpenOptions;
    ///
    /// let file = OpenOptions::new().write(true).open("foo.txt");
    /// ```
    pub fn write(&mut self, write: bool) -> &mut Self {
        self.0.write(write);
        self
    }

    /// Sets the option for the append mode.
    ///
    /// This option, when true, means that writes will append to a file instead
    /// of overwriting previous contents.
    /// Note that setting `.write(true).append(true)` has the same effect as
    /// setting only `.append(true)`.
    ///
    /// For most filesystems, the operating system guarantees that all writes are
    /// atomic: no writes get mangled because another process writes at the same
    /// time.
    ///
    /// One maybe obvious note when using append-mode: make sure that all data
    /// that belongs together is written to the file in one operation. This
    /// can be done by concatenating strings before passing them to [`write()`],
    /// or using a buffered writer (with a buffer of adequate size),
    /// and calling [`flush()`] when the message is complete.
    ///
    /// If a file is opened with both read and append access, beware that after
    /// opening, and after every write, the position for reading may be set at the
    /// end of the file. So, before writing, save the current position (using
    /// [`seek`]`(`[`SeekFrom`]`::`[`Current`]`(0))`), and restore it before the next read.
    ///
    /// ## Note
    ///
    /// This function doesn't create the file if it doesn't exist. Use the
    /// [`OpenOptions::create`] method to do so.
    ///
    /// [`write()`]: Write::write
    /// [`flush()`]: Write::flush
    /// [`seek`]: Seek::seek
    /// [`Current`]: SeekFrom::Current
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::OpenOptions;
    ///
    /// let file = OpenOptions::new().append(true).open("foo.txt");
    /// ```
    pub fn append(&mut self, append: bool) -> &mut Self {
        self.0.append(append);
        self
    }

    /// Sets the option for truncating a previous file.
    ///
    /// If a file is successfully opened with this option set it will truncate
    /// the file to 0 length if it already exists.
    ///
    /// The file must be opened with write access for truncate to work.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::OpenOptions;
    ///
    /// let file = OpenOptions::new().write(true).truncate(true).open("foo.txt");
    /// ```
    pub fn truncate(&mut self, truncate: bool) -> &mut Self {
        self.0.truncate(truncate);
        self
    }

    /// Sets the option to create a new file, or open it if it already exists.
    ///
    /// In order for the file to be created, [`OpenOptions::write`] or
    /// [`OpenOptions::append`] access must be used.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::OpenOptions;
    ///
    /// let file = OpenOptions::new().write(true).create(true).open("foo.txt");
    /// ```
    pub fn create(&mut self, create: bool) -> &mut Self {
        self.0.create(create);
        self
    }

    /// Sets the option to create a new file, failing if it already exists.
    ///
    /// No file is allowed to exist at the target location, also no (dangling) symlink. In this
    /// way, if the call succeeds, the file returned is guaranteed to be new.
    ///
    /// This option is useful because it is atomic. Otherwise between checking
    /// whether a file exists and creating a new one, the file may have been
    /// created by another process (a TOCTOU race condition / attack).
    ///
    /// If `.create_new(true)` is set, [`.create()`] and [`.truncate()`] are
    /// ignored.
    ///
    /// The file must be opened with write or append access in order to create
    /// a new file.
    ///
    /// [`.create()`]: OpenOptions::create
    /// [`.truncate()`]: OpenOptions::truncate
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::OpenOptions;
    ///
    /// let file = OpenOptions::new().write(true)
    ///                              .create_new(true)
    ///                              .open("foo.txt");
    /// ```
    pub fn create_new(&mut self, create_new: bool) -> &mut Self {
        self.0.create_new(create_new);
        self
    }

    /// Opens a file at `path` with the options specified by `self`.
    ///
    /// # Errors
    ///
    /// This function will return an error under a number of different
    /// circumstances. Some of these error conditions are listed here, together
    /// with their [`io::ErrorKind`]. The mapping to [`io::ErrorKind`]s is not
    /// part of the compatibility contract of the function.
    ///
    /// * [`NotFound`]: The specified file does not exist and neither `create`
    ///   or `create_new` is set.
    /// * [`NotFound`]: One of the directory components of the file path does
    ///   not exist.
    /// * [`PermissionDenied`]: The user lacks permission to get the specified
    ///   access rights for the file.
    /// * [`PermissionDenied`]: The user lacks permission to open one of the
    ///   directory components of the specified path.
    /// * [`AlreadyExists`]: `create_new` was specified and the file already
    ///   exists.
    /// * [`InvalidInput`]: Invalid combinations of open options (truncate
    ///   without write access, no access mode set, etc.).
    ///
    /// The following errors don't match any existing [`io::ErrorKind`] at the moment:
    /// * One of the directory components of the specified file path
    ///   was not, in fact, a directory.
    /// * Filesystem-level errors: full disk, write permission
    ///   requested on a read-only file system, exceeded disk quota, too many
    ///   open files, too long filename, too many symbolic links in the
    ///   specified path (Unix-like systems only), etc.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::OpenOptions;
    ///
    /// let file = OpenOptions::new().read(true).open("foo.txt");
    /// ```
    ///
    /// [`AlreadyExists`]: io::ErrorKind::AlreadyExists
    /// [`InvalidInput`]: io::ErrorKind::InvalidInput
    /// [`NotFound`]: io::ErrorKind::NotFound
    /// [`PermissionDenied`]: io::ErrorKind::PermissionDenied
    pub fn open<P: AsRef<Path>>(&self, path: P) -> io::Result<File> {
        self._open(path.as_ref())
    }

    fn _open(&self, path: &Path) -> io::Result<File> {
        fs_imp::File::open(path, &self.0).map(|inner| File { inner })
    }
}

impl AsInner<fs_imp::OpenOptions> for OpenOptions {
    fn as_inner(&self) -> &fs_imp::OpenOptions {
        &self.0
    }
}

impl AsInnerMut<fs_imp::OpenOptions> for OpenOptions {
    fn as_inner_mut(&mut self) -> &mut fs_imp::OpenOptions {
        &mut self.0
    }
}

impl Metadata {
    /// Returns the file type for this metadata.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// fn main() -> std::io::Result<()> {
    ///     use std::fs;
    ///
    ///     let metadata = fs::metadata("foo.txt")?;
    ///
    ///     println!("{:?}", metadata.file_type());
    ///     Ok(())
    /// }
    /// ```
    pub fn file_type(&self) -> FileType {
        FileType(self.0.file_type())
    }

    /// Returns `true` if this metadata is for a directory. The
    /// result is mutually exclusive to the result of
    /// [`Metadata::is_file`], and will be false for symlink metadata
    /// obtained from [`symlink_metadata`].
    ///
    /// # Examples
    ///
    /// ```no_run
    /// fn main() -> std::io::Result<()> {
    ///     use std::fs;
    ///
    ///     let metadata = fs::metadata("foo.txt")?;
    ///
    ///     assert!(!metadata.is_dir());
    ///     Ok(())
    /// }
    /// ```
    pub fn is_dir(&self) -> bool {
        self.file_type().is_dir()
    }

    /// Returns `true` if this metadata is for a regular file. The
    /// result is mutually exclusive to the result of
    /// [`Metadata::is_dir`], and will be false for symlink metadata
    /// obtained from [`symlink_metadata`].
    ///
    /// When the goal is simply to read from (or write to) the source, the most
    /// reliable way to test the source can be read (or written to) is to open
    /// it. Only using `is_file` can break workflows like `diff <( prog_a )` on
    /// a Unix-like system for example. See [`File::open`] or
    /// [`OpenOptions::open`] for more information.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let metadata = fs::metadata("foo.txt")?;
    ///
    ///     assert!(metadata.is_file());
    ///     Ok(())
    /// }
    /// ```
    pub fn is_file(&self) -> bool {
        self.file_type().is_file()
    }

    /// Returns `true` if this metadata is for a symbolic link.
    ///
    /// # Examples
    ///
    #[cfg_attr(unix, doc = "```no_run")]
    #[cfg_attr(not(unix), doc = "```ignore")]
    /// #![feature(is_symlink)]
    /// use std::fs;
    /// use std::path::Path;
    /// use std::os::unix::fs::symlink;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let link_path = Path::new("link");
    ///     symlink("/origin_does_not_exists/", link_path)?;
    ///
    ///     let metadata = fs::symlink_metadata(link_path)?;
    ///
    ///     assert!(metadata.is_symlink());
    ///     Ok(())
    /// }
    /// ```
    pub fn is_symlink(&self) -> bool {
        self.file_type().is_symlink()
    }

    /// Returns the size of the file, in bytes, this metadata is for.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let metadata = fs::metadata("foo.txt")?;
    ///
    ///     assert_eq!(0, metadata.len());
    ///     Ok(())
    /// }
    /// ```
    pub fn len(&self) -> u64 {
        self.0.size()
    }

    /// Returns the permissions of the file this metadata is for.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let metadata = fs::metadata("foo.txt")?;
    ///
    ///     assert!(!metadata.permissions().readonly());
    ///     Ok(())
    /// }
    /// ```
    pub fn permissions(&self) -> Permissions {
        Permissions(self.0.perm())
    }

    /// Returns the last modification time listed in this metadata.
    ///
    /// The returned value corresponds to the `mtime` field of `stat` on Unix
    /// platforms and the `ftLastWriteTime` field on Windows platforms.
    ///
    /// # Errors
    ///
    /// This field might not be available on all platforms, and will return an
    /// `Err` on platforms where it is not available.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let metadata = fs::metadata("foo.txt")?;
    ///
    ///     if let Ok(time) = metadata.modified() {
    ///         println!("{:?}", time);
    ///     } else {
    ///         println!("Not supported on this platform");
    ///     }
    ///     Ok(())
    /// }
    /// ```
    pub fn modified(&self) -> io::Result<SystemTime> {
        self.0.modified().map(FromInner::from_inner)
    }

    /// Returns the last access time of this metadata.
    ///
    /// The returned value corresponds to the `atime` field of `stat` on Unix
    /// platforms and the `ftLastAccessTime` field on Windows platforms.
    ///
    /// Note that not all platforms will keep this field update in a file's
    /// metadata, for example Windows has an option to disable updating this
    /// time when files are accessed and Linux similarly has `noatime`.
    ///
    /// # Errors
    ///
    /// This field might not be available on all platforms, and will return an
    /// `Err` on platforms where it is not available.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let metadata = fs::metadata("foo.txt")?;
    ///
    ///     if let Ok(time) = metadata.accessed() {
    ///         println!("{:?}", time);
    ///     } else {
    ///         println!("Not supported on this platform");
    ///     }
    ///     Ok(())
    /// }
    /// ```
    pub fn accessed(&self) -> io::Result<SystemTime> {
        self.0.accessed().map(FromInner::from_inner)
    }

    /// Returns the creation time listed in this metadata.
    ///
    /// The returned value corresponds to the `btime` field of `statx` on
    /// Linux kernel starting from to 4.11, the `birthtime` field of `stat` on other
    /// Unix platforms, and the `ftCreationTime` field on Windows platforms.
    ///
    /// # Errors
    ///
    /// This field might not be available on all platforms, and will return an
    /// `Err` on platforms or filesystems where it is not available.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let metadata = fs::metadata("foo.txt")?;
    ///
    ///     if let Ok(time) = metadata.created() {
    ///         println!("{:?}", time);
    ///     } else {
    ///         println!("Not supported on this platform or filesystem");
    ///     }
    ///     Ok(())
    /// }
    /// ```
    pub fn created(&self) -> io::Result<SystemTime> {
        self.0.created().map(FromInner::from_inner)
    }
}

impl fmt::Debug for Metadata {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Metadata")
            .field("file_type", &self.file_type())
            .field("is_dir", &self.is_dir())
            .field("is_file", &self.is_file())
            .field("permissions", &self.permissions())
            .field("modified", &self.modified())
            .field("accessed", &self.accessed())
            .field("created", &self.created())
            .finish_non_exhaustive()
    }
}

impl AsInner<fs_imp::FileAttr> for Metadata {
    fn as_inner(&self) -> &fs_imp::FileAttr {
        &self.0
    }
}

impl FromInner<fs_imp::FileAttr> for Metadata {
    fn from_inner(attr: fs_imp::FileAttr) -> Metadata {
        Metadata(attr)
    }
}

impl Permissions {
    /// Returns `true` if these permissions describe a readonly (unwritable) file.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let mut f = File::create("foo.txt")?;
    ///     let metadata = f.metadata()?;
    ///
    ///     assert_eq!(false, metadata.permissions().readonly());
    ///     Ok(())
    /// }
    /// ```
    pub fn readonly(&self) -> bool {
        self.0.readonly()
    }

    /// Modifies the readonly flag for this set of permissions. If the
    /// `readonly` argument is `true`, using the resulting `Permission` will
    /// update file permissions to forbid writing. Conversely, if it's `false`,
    /// using the resulting `Permission` will update file permissions to allow
    /// writing.
    ///
    /// This operation does **not** modify the filesystem. To modify the
    /// filesystem use the [`set_permissions`] function.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let f = File::create("foo.txt")?;
    ///     let metadata = f.metadata()?;
    ///     let mut permissions = metadata.permissions();
    ///
    ///     permissions.set_readonly(true);
    ///
    ///     // filesystem doesn't change
    ///     assert_eq!(false, metadata.permissions().readonly());
    ///
    ///     // just this particular `permissions`.
    ///     assert_eq!(true, permissions.readonly());
    ///     Ok(())
    /// }
    /// ```
    pub fn set_readonly(&mut self, readonly: bool) {
        self.0.set_readonly(readonly)
    }
}

impl FileType {
    /// Tests whether this file type represents a directory. The
    /// result is mutually exclusive to the results of
    /// [`is_file`] and [`is_symlink`]; only zero or one of these
    /// tests may pass.
    ///
    /// [`is_file`]: FileType::is_file
    /// [`is_symlink`]: FileType::is_symlink
    ///
    /// # Examples
    ///
    /// ```no_run
    /// fn main() -> std::io::Result<()> {
    ///     use std::fs;
    ///
    ///     let metadata = fs::metadata("foo.txt")?;
    ///     let file_type = metadata.file_type();
    ///
    ///     assert_eq!(file_type.is_dir(), false);
    ///     Ok(())
    /// }
    /// ```
    pub fn is_dir(&self) -> bool {
        self.0.is_dir()
    }

    /// Tests whether this file type represents a regular file.
    /// The result is  mutually exclusive to the results of
    /// [`is_dir`] and [`is_symlink`]; only zero or one of these
    /// tests may pass.
    ///
    /// When the goal is simply to read from (or write to) the source, the most
    /// reliable way to test the source can be read (or written to) is to open
    /// it. Only using `is_file` can break workflows like `diff <( prog_a )` on
    /// a Unix-like system for example. See [`File::open`] or
    /// [`OpenOptions::open`] for more information.
    ///
    /// [`is_dir`]: FileType::is_dir
    /// [`is_symlink`]: FileType::is_symlink
    ///
    /// # Examples
    ///
    /// ```no_run
    /// fn main() -> std::io::Result<()> {
    ///     use std::fs;
    ///
    ///     let metadata = fs::metadata("foo.txt")?;
    ///     let file_type = metadata.file_type();
    ///
    ///     assert_eq!(file_type.is_file(), true);
    ///     Ok(())
    /// }
    /// ```
    pub fn is_file(&self) -> bool {
        self.0.is_file()
    }

    /// Tests whether this file type represents a symbolic link.
    /// The result is mutually exclusive to the results of
    /// [`is_dir`] and [`is_file`]; only zero or one of these
    /// tests may pass.
    ///
    /// The underlying [`Metadata`] struct needs to be retrieved
    /// with the [`fs::symlink_metadata`] function and not the
    /// [`fs::metadata`] function. The [`fs::metadata`] function
    /// follows symbolic links, so [`is_symlink`] would always
    /// return `false` for the target file.
    ///
    /// [`fs::metadata`]: metadata
    /// [`fs::symlink_metadata`]: symlink_metadata
    /// [`is_dir`]: FileType::is_dir
    /// [`is_file`]: FileType::is_file
    /// [`is_symlink`]: FileType::is_symlink
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let metadata = fs::symlink_metadata("foo.txt")?;
    ///     let file_type = metadata.file_type();
    ///
    ///     assert_eq!(file_type.is_symlink(), false);
    ///     Ok(())
    /// }
    /// ```
    pub fn is_symlink(&self) -> bool {
        self.0.is_symlink()
    }
}

impl AsInner<fs_imp::FileType> for FileType {
    fn as_inner(&self) -> &fs_imp::FileType {
        &self.0
    }
}

impl FromInner<fs_imp::FilePermissions> for Permissions {
    fn from_inner(f: fs_imp::FilePermissions) -> Permissions {
        Permissions(f)
    }
}

impl AsInner<fs_imp::FilePermissions> for Permissions {
    fn as_inner(&self) -> &fs_imp::FilePermissions {
        &self.0
    }
}

impl Iterator for ReadDir {
    type Item = io::Result<DirEntry>;

    fn next(&mut self) -> Option<io::Result<DirEntry>> {
        self.0.next().map(|entry| entry.map(DirEntry))
    }
}

impl DirEntry {
    /// Returns the full path to the file that this entry represents.
    ///
    /// The full path is created by joining the original path to `read_dir`
    /// with the filename of this entry.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     for entry in fs::read_dir(".")? {
    ///         let dir = entry?;
    ///         println!("{:?}", dir.path());
    ///     }
    ///     Ok(())
    /// }
    /// ```
    ///
    /// This prints output like:
    ///
    /// ```text
    /// "./whatever.txt"
    /// "./foo.html"
    /// "./hello_world.rs"
    /// ```
    ///
    /// The exact text, of course, depends on what files you have in `.`.
    pub fn path(&self) -> PathBuf {
        self.0.path()
    }

    /// Returns the metadata for the file that this entry points at.
    ///
    /// This function will not traverse symlinks if this entry points at a
    /// symlink. To traverse symlinks use [`fs::metadata`] or [`fs::File::metadata`].
    ///
    /// [`fs::metadata`]: metadata
    /// [`fs::File::metadata`]: File::metadata
    ///
    /// # Platform-specific behavior
    ///
    /// On Windows this function is cheap to call (no extra system calls
    /// needed), but on Unix platforms this function is the equivalent of
    /// calling `symlink_metadata` on the path.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fs;
    ///
    /// if let Ok(entries) = fs::read_dir(".") {
    ///     for entry in entries {
    ///         if let Ok(entry) = entry {
    ///             // Here, `entry` is a `DirEntry`.
    ///             if let Ok(metadata) = entry.metadata() {
    ///                 // Now let's show our entry's permissions!
    ///                 println!("{:?}: {:?}", entry.path(), metadata.permissions());
    ///             } else {
    ///                 println!("Couldn't get metadata for {:?}", entry.path());
    ///             }
    ///         }
    ///     }
    /// }
    /// ```
    pub fn metadata(&self) -> io::Result<Metadata> {
        self.0.metadata().map(Metadata)
    }

    /// Returns the file type for the file that this entry points at.
    ///
    /// This function will not traverse symlinks if this entry points at a
    /// symlink.
    ///
    /// # Platform-specific behavior
    ///
    /// On Windows and most Unix platforms this function is free (no extra
    /// system calls needed), but some Unix platforms may require the equivalent
    /// call to `symlink_metadata` to learn about the target file type.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fs;
    ///
    /// if let Ok(entries) = fs::read_dir(".") {
    ///     for entry in entries {
    ///         if let Ok(entry) = entry {
    ///             // Here, `entry` is a `DirEntry`.
    ///             if let Ok(file_type) = entry.file_type() {
    ///                 // Now let's show our entry's file type!
    ///                 println!("{:?}: {:?}", entry.path(), file_type);
    ///             } else {
    ///                 println!("Couldn't get file type for {:?}", entry.path());
    ///             }
    ///         }
    ///     }
    /// }
    /// ```
    pub fn file_type(&self) -> io::Result<FileType> {
        self.0.file_type().map(FileType)
    }

    /// Returns the bare file name of this directory entry without any other
    /// leading path component.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fs;
    ///
    /// if let Ok(entries) = fs::read_dir(".") {
    ///     for entry in entries {
    ///         if let Ok(entry) = entry {
    ///             // Here, `entry` is a `DirEntry`.
    ///             println!("{:?}", entry.file_name());
    ///         }
    ///     }
    /// }
    /// ```
    pub fn file_name(&self) -> OsString {
        self.0.file_name()
    }
}

impl fmt::Debug for DirEntry {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_tuple("DirEntry").field(&self.path()).finish()
    }
}

impl AsInner<fs_imp::DirEntry> for DirEntry {
    fn as_inner(&self) -> &fs_imp::DirEntry {
        &self.0
    }
}

/// Removes a file from the filesystem.
///
/// Note that there is no
/// guarantee that the file is immediately deleted (e.g., depending on
/// platform, other open file descriptors may prevent immediate removal).
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `unlink` function on Unix
/// and the `DeleteFile` function on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * `path` points to a directory.
/// * The file doesn't exist.
/// * The user lacks permissions to remove the file.
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::remove_file("a.txt")?;
///     Ok(())
/// }
/// ```
#[doc(alias = "delete")]
pub fn remove_file<P: AsRef<Path>>(path: P) -> io::Result<()> {
    fs_imp::unlink(path.as_ref())
}

/// Given a path, query the file system to get information about a file,
/// directory, etc.
///
/// This function will traverse symbolic links to query information about the
/// destination file.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `stat` function on Unix
/// and the `GetFileAttributesEx` function on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * The user lacks permissions to perform `metadata` call on `path`.
/// * `path` does not exist.
///
/// # Examples
///
/// ```rust,no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     let attr = fs::metadata("/some/file/path.txt")?;
///     // inspect attr ...
///     Ok(())
/// }
/// ```
pub fn metadata<P: AsRef<Path>>(path: P) -> io::Result<Metadata> {
    fs_imp::stat(path.as_ref()).map(Metadata)
}

/// Query the metadata about a file without following symlinks.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `lstat` function on Unix
/// and the `GetFileAttributesEx` function on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * The user lacks permissions to perform `metadata` call on `path`.
/// * `path` does not exist.
///
/// # Examples
///
/// ```rust,no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     let attr = fs::symlink_metadata("/some/file/path.txt")?;
///     // inspect attr ...
///     Ok(())
/// }
/// ```
pub fn symlink_metadata<P: AsRef<Path>>(path: P) -> io::Result<Metadata> {
    fs_imp::lstat(path.as_ref()).map(Metadata)
}

/// Rename a file or directory to a new name, replacing the original file if
/// `to` already exists.
///
/// This will not work if the new name is on a different mount point.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `rename` function on Unix
/// and the `MoveFileEx` function with the `MOVEFILE_REPLACE_EXISTING` flag on Windows.
///
/// Because of this, the behavior when both `from` and `to` exist differs. On
/// Unix, if `from` is a directory, `to` must also be an (empty) directory. If
/// `from` is not a directory, `to` must also be not a directory. In contrast,
/// on Windows, `from` can be anything, but `to` must *not* be a directory.
///
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * `from` does not exist.
/// * The user lacks permissions to view contents.
/// * `from` and `to` are on separate filesystems.
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::rename("a.txt", "b.txt")?; // Rename a.txt to b.txt
///     Ok(())
/// }
/// ```
pub fn rename<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> io::Result<()> {
    fs_imp::rename(from.as_ref(), to.as_ref())
}

/// Copies the contents of one file to another. This function will also
/// copy the permission bits of the original file to the destination file.
///
/// This function will **overwrite** the contents of `to`.
///
/// Note that if `from` and `to` both point to the same file, then the file
/// will likely get truncated by this operation.
///
/// On success, the total number of bytes copied is returned and it is equal to
/// the length of the `to` file as reported by `metadata`.
///
/// If you’re wanting to copy the contents of one file to another and you’re
/// working with [`File`]s, see the [`io::copy()`] function.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `open` function in Unix
/// with `O_RDONLY` for `from` and `O_WRONLY`, `O_CREAT`, and `O_TRUNC` for `to`.
/// `O_CLOEXEC` is set for returned file descriptors.
/// On Windows, this function currently corresponds to `CopyFileEx`. Alternate
/// NTFS streams are copied but only the size of the main stream is returned by
/// this function. On MacOS, this function corresponds to `fclonefileat` and
/// `fcopyfile`.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * `from` is neither a regular file nor a symlink to a regular file.
/// * `from` does not exist.
/// * The current process does not have the permission rights to read
///   `from` or write `to`.
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::copy("foo.txt", "bar.txt")?;  // Copy foo.txt to bar.txt
///     Ok(())
/// }
/// ```
pub fn copy<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> io::Result<u64> {
    fs_imp::copy(from.as_ref(), to.as_ref())
}

/// Creates a new hard link on the filesystem.
///
/// The `link` path will be a link pointing to the `original` path. Note that
/// systems often require these two paths to both be located on the same
/// filesystem.
///
/// If `original` names a symbolic link, it is platform-specific whether the
/// symbolic link is followed. On platforms where it's possible to not follow
/// it, it is not followed, and the created hard link points to the symbolic
/// link itself.
///
/// # Platform-specific behavior
///
/// This function currently corresponds the `CreateHardLink` function on Windows.
/// On most Unix systems, it corresponds to the `linkat` function with no flags.
/// On Android, VxWorks, and Redox, it instead corresponds to the `link` function.
/// On MacOS, it uses the `linkat` function if it is available, but on very old
/// systems where `linkat` is not available, `link` is selected at runtime instead.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * The `original` path is not a file or doesn't exist.
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::hard_link("a.txt", "b.txt")?; // Hard link a.txt to b.txt
///     Ok(())
/// }
/// ```
pub fn hard_link<P: AsRef<Path>, Q: AsRef<Path>>(original: P, link: Q) -> io::Result<()> {
    fs_imp::link(original.as_ref(), link.as_ref())
}

/// Creates a new symbolic link on the filesystem.
///
/// The `link` path will be a symbolic link pointing to the `original` path.
/// On Windows, this will be a file symlink, not a directory symlink;
/// for this reason, the platform-specific [`std::os::unix::fs::symlink`]
/// and [`std::os::windows::fs::symlink_file`] or [`symlink_dir`] should be
/// used instead to make the intent explicit.
///
/// [`std::os::unix::fs::symlink`]: crate::os::unix::fs::symlink
/// [`std::os::windows::fs::symlink_file`]: crate::os::windows::fs::symlink_file
/// [`symlink_dir`]: crate::os::windows::fs::symlink_dir
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::soft_link("a.txt", "b.txt")?;
///     Ok(())
/// }
/// ```
pub fn soft_link<P: AsRef<Path>, Q: AsRef<Path>>(original: P, link: Q) -> io::Result<()> {
    fs_imp::symlink(original.as_ref(), link.as_ref())
}

/// Reads a symbolic link, returning the file that the link points to.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `readlink` function on Unix
/// and the `CreateFile` function with `FILE_FLAG_OPEN_REPARSE_POINT` and
/// `FILE_FLAG_BACKUP_SEMANTICS` flags on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * `path` is not a symbolic link.
/// * `path` does not exist.
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     let path = fs::read_link("a.txt")?;
///     Ok(())
/// }
/// ```
pub fn read_link<P: AsRef<Path>>(path: P) -> io::Result<PathBuf> {
    fs_imp::readlink(path.as_ref())
}

/// Returns the canonical, absolute form of a path with all intermediate
/// components normalized and symbolic links resolved.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `realpath` function on Unix
/// and the `CreateFile` and `GetFinalPathNameByHandle` functions on Windows.
/// Note that, this [may change in the future][changes].
///
/// On Windows, this converts the path to use [extended length path][path]
/// syntax, which allows your program to use longer path names, but means you
/// can only join backslash-delimited paths to it, and it may be incompatible
/// with other applications (if passed to the application on the command-line,
/// or written to a file another application may read).
///
/// [changes]: io#platform-specific-behavior
/// [path]: https://docs.microsoft.com/en-us/windows/win32/fileio/naming-a-file
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * `path` does not exist.
/// * A non-final component in path is not a directory.
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     let path = fs::canonicalize("../a/../foo.txt")?;
///     Ok(())
/// }
/// ```
pub fn canonicalize<P: AsRef<Path>>(path: P) -> io::Result<PathBuf> {
    fs_imp::canonicalize(path.as_ref())
}

/// Creates a new, empty directory at the provided path
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `mkdir` function on Unix
/// and the `CreateDirectory` function on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// **NOTE**: If a parent of the given path doesn't exist, this function will
/// return an error. To create a directory and all its missing parents at the
/// same time, use the [`create_dir_all`] function.
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * User lacks permissions to create directory at `path`.
/// * A parent of the given path doesn't exist. (To create a directory and all
///   its missing parents at the same time, use the [`create_dir_all`]
///   function.)
/// * `path` already exists.
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::create_dir("/some/dir")?;
///     Ok(())
/// }
/// ```
#[doc(alias = "mkdir")]
pub fn create_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
    DirBuilder::new().create(path.as_ref())
}

/// Recursively create a directory and all of its parent components if they
/// are missing.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `mkdir` function on Unix
/// and the `CreateDirectory` function on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * If any directory in the path specified by `path`
/// does not already exist and it could not be created otherwise. The specific
/// error conditions for when a directory is being created (after it is
/// determined to not exist) are outlined by [`fs::create_dir`].
///
/// Notable exception is made for situations where any of the directories
/// specified in the `path` could not be created as it was being created concurrently.
/// Such cases are considered to be successful. That is, calling `create_dir_all`
/// concurrently from multiple threads or processes is guaranteed not to fail
/// due to a race condition with itself.
///
/// [`fs::create_dir`]: create_dir
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::create_dir_all("/some/dir")?;
///     Ok(())
/// }
/// ```
pub fn create_dir_all<P: AsRef<Path>>(path: P) -> io::Result<()> {
    DirBuilder::new().recursive(true).create(path.as_ref())
}

/// Removes an empty directory.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `rmdir` function on Unix
/// and the `RemoveDirectory` function on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * `path` doesn't exist.
/// * `path` isn't a directory.
/// * The user lacks permissions to remove the directory at the provided `path`.
/// * The directory isn't empty.
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::remove_dir("/some/dir")?;
///     Ok(())
/// }
/// ```
#[doc(alias = "rmdir")]
pub fn remove_dir<P: AsRef<Path>>(path: P) -> io::Result<()> {
    fs_imp::rmdir(path.as_ref())
}

/// Removes a directory at this path, after removing all its contents. Use
/// carefully!
///
/// This function does **not** follow symbolic links and it will simply remove the
/// symbolic link itself.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to `opendir`, `lstat`, `rm` and `rmdir` functions on Unix
/// and the `FindFirstFile`, `GetFileAttributesEx`, `DeleteFile`, and `RemoveDirectory` functions
/// on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// See [`fs::remove_file`] and [`fs::remove_dir`].
///
/// [`fs::remove_file`]: remove_file
/// [`fs::remove_dir`]: remove_dir
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::remove_dir_all("/some/dir")?;
///     Ok(())
/// }
/// ```
#[doc(alias = "delete")]
pub fn remove_dir_all<P: AsRef<Path>>(path: P) -> io::Result<()> {
    fs_imp::remove_dir_all(path.as_ref())
}

/// Returns an iterator over the entries within a directory.
///
/// The iterator will yield instances of [`io::Result`]`<`[`DirEntry`]`>`.
/// New errors may be encountered after an iterator is initially constructed.
/// Entries for the current and parent directories (typically `.` and `..`) are
/// skipped.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `opendir` function on Unix
/// and the `FindFirstFile` function on Windows. Advancing the iterator
/// currently corresponds to `readdir` on Unix and `FindNextFile` on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// The order in which this iterator returns entries is platform and filesystem
/// dependent.
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * The provided `path` doesn't exist.
/// * The process lacks permissions to view the contents.
/// * The `path` points at a non-directory file.
///
/// # Examples
///
/// ```
/// use std::io;
/// use std::fs::{self, DirEntry};
/// use std::path::Path;
///
/// // one possible implementation of walking a directory only visiting files
/// fn visit_dirs(dir: &Path, cb: &dyn Fn(&DirEntry)) -> io::Result<()> {
///     if dir.is_dir() {
///         for entry in fs::read_dir(dir)? {
///             let entry = entry?;
///             let path = entry.path();
///             if path.is_dir() {
///                 visit_dirs(&path, cb)?;
///             } else {
///                 cb(&entry);
///             }
///         }
///     }
///     Ok(())
/// }
/// ```
///
/// ```rust,no_run
/// use std::{fs, io};
///
/// fn main() -> io::Result<()> {
///     let mut entries = fs::read_dir(".")?
///         .map(|res| res.map(|e| e.path()))
///         .collect::<Result<Vec<_>, io::Error>>()?;
///
///     // The order in which `read_dir` returns entries is not guaranteed. If reproducible
///     // ordering is required the entries should be explicitly sorted.
///
///     entries.sort();
///
///     // The entries have now been sorted by their path.
///
///     Ok(())
/// }
/// ```
pub fn read_dir<P: AsRef<Path>>(path: P) -> io::Result<ReadDir> {
    fs_imp::readdir(path.as_ref()).map(ReadDir)
}

/// Changes the permissions found on a file or a directory.
///
/// # Platform-specific behavior
///
/// This function currently corresponds to the `chmod` function on Unix
/// and the `SetFileAttributes` function on Windows.
/// Note that, this [may change in the future][changes].
///
/// [changes]: io#platform-specific-behavior
///
/// # Errors
///
/// This function will return an error in the following situations, but is not
/// limited to just these cases:
///
/// * `path` does not exist.
/// * The user lacks the permission to change attributes of the file.
///
/// # Examples
///
/// ```no_run
/// use std::fs;
///
/// fn main() -> std::io::Result<()> {
///     let mut perms = fs::metadata("foo.txt")?.permissions();
///     perms.set_readonly(true);
///     fs::set_permissions("foo.txt", perms)?;
///     Ok(())
/// }
/// ```
pub fn set_permissions<P: AsRef<Path>>(path: P, perm: Permissions) -> io::Result<()> {
    fs_imp::set_perm(path.as_ref(), perm.0)
}

impl DirBuilder {
    /// Creates a new set of options with default mode/security settings for all
    /// platforms and also non-recursive.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fs::DirBuilder;
    ///
    /// let builder = DirBuilder::new();
    /// ```
    pub fn new() -> DirBuilder {
        DirBuilder { inner: fs_imp::DirBuilder::new(), recursive: false }
    }

    /// Indicates that directories should be created recursively, creating all
    /// parent directories. Parents that do not exist are created with the same
    /// security and permissions settings.
    ///
    /// This option defaults to `false`.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fs::DirBuilder;
    ///
    /// let mut builder = DirBuilder::new();
    /// builder.recursive(true);
    /// ```
    pub fn recursive(&mut self, recursive: bool) -> &mut Self {
        self.recursive = recursive;
        self
    }

    /// Creates the specified directory with the options configured in this
    /// builder.
    ///
    /// It is considered an error if the directory already exists unless
    /// recursive mode is enabled.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::{self, DirBuilder};
    ///
    /// let path = "/tmp/foo/bar/baz";
    /// DirBuilder::new()
    ///     .recursive(true)
    ///     .create(path).unwrap();
    ///
    /// assert!(fs::metadata(path).unwrap().is_dir());
    /// ```
    pub fn create<P: AsRef<Path>>(&self, path: P) -> io::Result<()> {
        self._create(path.as_ref())
    }

    fn _create(&self, path: &Path) -> io::Result<()> {
        if self.recursive { self.create_dir_all(path) } else { self.inner.mkdir(path) }
    }

    fn create_dir_all(&self, path: &Path) -> io::Result<()> {
        if path == Path::new("") {
            return Ok(());
        }

        match self.inner.mkdir(path) {
            Ok(()) => return Ok(()),
            Err(ref e) if e.kind() == io::ErrorKind::NotFound => {}
            Err(_) if path.is_dir() => return Ok(()),
            Err(e) => return Err(e),
        }
        match path.parent() {
            Some(p) => self.create_dir_all(p)?,
            None => {
                return Err(io::Error::new_const(
                    io::ErrorKind::Uncategorized,
                    &"failed to create whole tree",
                ));
            }
        }
        match self.inner.mkdir(path) {
            Ok(()) => Ok(()),
            Err(_) if path.is_dir() => Ok(()),
            Err(e) => Err(e),
        }
    }
}

impl AsInnerMut<fs_imp::DirBuilder> for DirBuilder {
    fn as_inner_mut(&mut self) -> &mut fs_imp::DirBuilder {
        &mut self.inner
    }
}

/// Returns `Ok(true)` if the path points at an existing entity.
///
/// This function will traverse symbolic links to query information about the
/// destination file. In case of broken symbolic links this will return `Ok(false)`.
///
/// As opposed to the `exists()` method, this one doesn't silently ignore errors
/// unrelated to the path not existing. (E.g. it will return `Err(_)` in case of permission
/// denied on some of the parent directories.)
///
/// # Examples
///
/// ```no_run
/// #![feature(path_try_exists)]
/// use std::fs;
///
/// assert!(!fs::try_exists("does_not_exist.txt").expect("Can't check existence of file does_not_exist.txt"));
/// assert!(fs::try_exists("/root/secret_file.txt").is_err());
/// ```
// FIXME: stabilization should modify documentation of `exists()` to recommend this method
// instead.
#[inline]
pub fn try_exists<P: AsRef<Path>>(path: P) -> io::Result<bool> {
    fs_imp::try_exists(path.as_ref())
}