#![stable(feature = "rust1", since = "1.0.0")]

use crate::fs::{self, Permissions};
use crate::io;
use crate::path::Path;
use crate::sys;
use crate::sys::platform::fs::MetadataExt as UnixMetadataExt;
use crate::sys_common::{AsInner, AsInnerMut, FromInner};

/// Unix-specific extensions to [`fs::File`].
#[stable(feature = "file_offset", since = "1.15.0")]
pub trait FileExt {
    /// Reads a number of bytes starting from a given offset.
    ///
    /// Returns the number of bytes read.
    ///
    /// The offset is relative to the start of the file and thus independent
    /// from the current cursor.
    ///
    /// The current file cursor is not affected by this function.
    ///
    /// Note that similar to [`File::read`], it is not an error to return with a
    /// short read.
    ///
    /// [`File::read`]: fs::File::read
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::io;
    /// use std::fs::File;
    /// use std::os::unix::prelude::FileExt;
    ///
    /// fn main() -> io::Result<()> {
    ///     let mut buf = [0u8; 8];
    ///     let file = File::open("foo.txt")?;
    ///
    ///     // We now read 8 bytes from the offset 10.
    ///     let num_bytes_read = file.read_at(&mut buf, 10)?;
    ///     println!("read {} bytes: {:?}", num_bytes_read, buf);
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "file_offset", since = "1.15.0")]
    fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize>;

    /// Reads the exact number of byte required to fill `buf` from the given offset.
    ///
    /// The offset is relative to the start of the file and thus independent
    /// from the current cursor.
    ///
    /// The current file cursor is not affected by this function.
    ///
    /// Similar to [`Read::read_exact`] but uses [`read_at`] instead of `read`.
    ///
    /// [`Read::read_exact`]: io::Read::read_exact
    /// [`read_at`]: FileExt::read_at
    ///
    /// # Errors
    ///
    /// If this function encounters an error of the kind
    /// [`ErrorKind::Interrupted`] then the error is ignored and the operation
    /// will continue.
    ///
    /// If this function encounters an "end of file" before completely filling
    /// the buffer, it returns an error of the kind [`ErrorKind::UnexpectedEof`].
    /// The contents of `buf` are unspecified in this case.
    ///
    /// If any other read error is encountered then this function immediately
    /// returns. The contents of `buf` are unspecified in this case.
    ///
    /// If this function returns an error, it is unspecified how many bytes it
    /// has read, but it will never read more than would be necessary to
    /// completely fill the buffer.
    ///
    /// [`ErrorKind::Interrupted`]: io::ErrorKind::Interrupted
    /// [`ErrorKind::UnexpectedEof`]: io::ErrorKind::UnexpectedEof
    ///
    /// # Examples
    ///
    /// ```no_run
    /// #![feature(rw_exact_all_at)]
    /// use std::io;
    /// use std::fs::File;
    /// use std::os::unix::prelude::FileExt;
    ///
    /// fn main() -> io::Result<()> {
    ///     let mut buf = [0u8; 8];
    ///     let file = File::open("foo.txt")?;
    ///
    ///     // We now read exactly 8 bytes from the offset 10.
    ///     file.read_exact_at(&mut buf, 10)?;
    ///     println!("read {} bytes: {:?}", buf.len(), buf);
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "rw_exact_all_at", since = "1.33.0")]
    fn read_exact_at(&self, mut buf: &mut [u8], mut offset: u64) -> io::Result<()> {
        while !buf.is_empty() {
            match self.read_at(buf, offset) {
                Ok(0) => break,
                Ok(n) => {
                    let tmp = buf;
                    buf = &mut tmp[n..];
                    offset += n as u64;
                }
                Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
                Err(e) => return Err(e),
            }
        }
        if !buf.is_empty() {
            Err(io::Error::new(io::ErrorKind::UnexpectedEof, "failed to fill whole buffer"))
        } else {
            Ok(())
        }
    }

    /// Writes a number of bytes starting from a given offset.
    ///
    /// Returns the number of bytes written.
    ///
    /// The offset is relative to the start of the file and thus independent
    /// from the current cursor.
    ///
    /// The current file cursor is not affected by this function.
    ///
    /// When writing beyond the end of the file, the file is appropriately
    /// extended and the intermediate bytes are initialized with the value 0.
    ///
    /// Note that similar to [`File::write`], it is not an error to return a
    /// short write.
    ///
    /// [`File::write`]: fs::File::write
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    /// use std::io;
    /// use std::os::unix::prelude::FileExt;
    ///
    /// fn main() -> io::Result<()> {
    ///     let file = File::open("foo.txt")?;
    ///
    ///     // We now write at the offset 10.
    ///     file.write_at(b"sushi", 10)?;
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "file_offset", since = "1.15.0")]
    fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize>;

    /// Attempts to write an entire buffer starting from a given offset.
    ///
    /// The offset is relative to the start of the file and thus independent
    /// from the current cursor.
    ///
    /// The current file cursor is not affected by this function.
    ///
    /// This method will continuously call [`write_at`] until there is no more data
    /// to be written or an error of non-[`ErrorKind::Interrupted`] kind is
    /// returned. This method will not return until the entire buffer has been
    /// successfully written or such an error occurs. The first error that is
    /// not of [`ErrorKind::Interrupted`] kind generated from this method will be
    /// returned.
    ///
    /// # Errors
    ///
    /// This function will return the first error of
    /// non-[`ErrorKind::Interrupted`] kind that [`write_at`] returns.
    ///
    /// [`ErrorKind::Interrupted`]: io::ErrorKind::Interrupted
    /// [`write_at`]: FileExt::write_at
    ///
    /// # Examples
    ///
    /// ```no_run
    /// #![feature(rw_exact_all_at)]
    /// use std::fs::File;
    /// use std::io;
    /// use std::os::unix::prelude::FileExt;
    ///
    /// fn main() -> io::Result<()> {
    ///     let file = File::open("foo.txt")?;
    ///
    ///     // We now write at the offset 10.
    ///     file.write_all_at(b"sushi", 10)?;
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "rw_exact_all_at", since = "1.33.0")]
    fn write_all_at(&self, mut buf: &[u8], mut offset: u64) -> io::Result<()> {
        while !buf.is_empty() {
            match self.write_at(buf, offset) {
                Ok(0) => {
                    return Err(io::Error::new(
                        io::ErrorKind::WriteZero,
                        "failed to write whole buffer",
                    ));
                }
                Ok(n) => {
                    buf = &buf[n..];
                    offset += n as u64
                }
                Err(ref e) if e.kind() == io::ErrorKind::Interrupted => {}
                Err(e) => return Err(e),
            }
        }
        Ok(())
    }
}

#[stable(feature = "file_offset", since = "1.15.0")]
impl FileExt for fs::File {
    fn read_at(&self, buf: &mut [u8], offset: u64) -> io::Result<usize> {
        self.as_inner().read_at(buf, offset)
    }
    fn write_at(&self, buf: &[u8], offset: u64) -> io::Result<usize> {
        self.as_inner().write_at(buf, offset)
    }
}

/// Unix-specific extensions to [`fs::Permissions`].
#[stable(feature = "fs_ext", since = "1.1.0")]
pub trait PermissionsExt {
    /// Returns the underlying raw `st_mode` bits that contain the standard
    /// Unix permissions for this file.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    /// use std::os::unix::fs::PermissionsExt;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let f = File::create("foo.txt")?;
    ///     let metadata = f.metadata()?;
    ///     let permissions = metadata.permissions();
    ///
    ///     println!("permissions: {}", permissions.mode());
    ///     Ok(()) }
    /// ```
    #[stable(feature = "fs_ext", since = "1.1.0")]
    fn mode(&self) -> u32;

    /// Sets the underlying raw bits for this set of permissions.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::File;
    /// use std::os::unix::fs::PermissionsExt;
    ///
    /// fn main() -> std::io::Result<()> {
    ///     let f = File::create("foo.txt")?;
    ///     let metadata = f.metadata()?;
    ///     let mut permissions = metadata.permissions();
    ///
    ///     permissions.set_mode(0o644); // Read/write for owner and read for others.
    ///     assert_eq!(permissions.mode(), 0o644);
    ///     Ok(()) }
    /// ```
    #[stable(feature = "fs_ext", since = "1.1.0")]
    fn set_mode(&mut self, mode: u32);

    /// Creates a new instance of `Permissions` from the given set of Unix
    /// permission bits.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fs::Permissions;
    /// use std::os::unix::fs::PermissionsExt;
    ///
    /// // Read/write for owner and read for others.
    /// let permissions = Permissions::from_mode(0o644);
    /// assert_eq!(permissions.mode(), 0o644);
    /// ```
    #[stable(feature = "fs_ext", since = "1.1.0")]
    fn from_mode(mode: u32) -> Self;
}

#[stable(feature = "fs_ext", since = "1.1.0")]
impl PermissionsExt for Permissions {
    fn mode(&self) -> u32 {
        self.as_inner().mode()
    }

    fn set_mode(&mut self, mode: u32) {
        *self = Permissions::from_inner(FromInner::from_inner(mode));
    }

    fn from_mode(mode: u32) -> Permissions {
        Permissions::from_inner(FromInner::from_inner(mode))
    }
}

/// Unix-specific extensions to [`fs::OpenOptions`].
#[stable(feature = "fs_ext", since = "1.1.0")]
pub trait OpenOptionsExt {
    /// Sets the mode bits that a new file will be created with.
    ///
    /// If a new file is created as part of an `OpenOptions::open` call then this
    /// specified `mode` will be used as the permission bits for the new file.
    /// If no `mode` is set, the default of `0o666` will be used.
    /// The operating system masks out bits with the system's `umask`, to produce
    /// the final permissions.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::OpenOptions;
    /// use std::os::unix::fs::OpenOptionsExt;
    ///
    /// # fn main() {
    /// let mut options = OpenOptions::new();
    /// options.mode(0o644); // Give read/write for owner and read for others.
    /// let file = options.open("foo.txt");
    /// # }
    /// ```
    #[stable(feature = "fs_ext", since = "1.1.0")]
    fn mode(&mut self, mode: u32) -> &mut Self;

    /// Pass custom flags to the `flags` argument of `open`.
    ///
    /// The bits that define the access mode are masked out with `O_ACCMODE`, to
    /// ensure they do not interfere with the access mode set by Rusts options.
    ///
    /// Custom flags can only set flags, not remove flags set by Rusts options.
    /// This options overwrites any previously set custom flags.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// # #![feature(libc)]
    /// extern crate libc;
    /// use std::fs::OpenOptions;
    /// use std::os::unix::fs::OpenOptionsExt;
    ///
    /// # fn main() {
    /// let mut options = OpenOptions::new();
    /// options.write(true);
    /// if cfg!(unix) {
    ///     options.custom_flags(libc::O_NOFOLLOW);
    /// }
    /// let file = options.open("foo.txt");
    /// # }
    /// ```
    #[stable(feature = "open_options_ext", since = "1.10.0")]
    fn custom_flags(&mut self, flags: i32) -> &mut Self;
}

/*#[stable(feature = "fs_ext", since = "1.1.0")]
impl OpenOptionsExt for OpenOptions {
    fn mode(&mut self, mode: u32) -> &mut OpenOptions {
        self.as_inner_mut().mode(mode); self
    }

    fn custom_flags(&mut self, flags: i32) -> &mut OpenOptions {
        self.as_inner_mut().custom_flags(flags); self
    }
}
*/

/// Unix-specific extensions to [`fs::Metadata`].
#[stable(feature = "metadata_ext", since = "1.1.0")]
pub trait MetadataExt {
    /// Returns the ID of the device containing the file.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::io;
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let dev_id = meta.dev();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn dev(&self) -> u64;
    /// Returns the inode number.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let inode = meta.ino();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn ino(&self) -> u64;
    /// Returns the rights applied to this file.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let mode = meta.mode();
    ///     let user_has_write_access      = mode & 0o200;
    ///     let user_has_read_write_access = mode & 0o600;
    ///     let group_has_read_access      = mode & 0o040;
    ///     let others_have_exec_access    = mode & 0o001;
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn mode(&self) -> u32;
    /// Returns the number of hard links pointing to this file.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let nb_hard_links = meta.nlink();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn nlink(&self) -> u64;
    /// Returns the user ID of the owner of this file.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let user_id = meta.uid();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn uid(&self) -> u32;
    /// Returns the group ID of the owner of this file.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let group_id = meta.gid();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn gid(&self) -> u32;
    /// Returns the device ID of this file (if it is a special one).
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let device_id = meta.rdev();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn rdev(&self) -> u64;
    /// Returns the total size of this file in bytes.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let file_size = meta.size();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn size(&self) -> u64;
    /// Returns the time of the last access to the file.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let last_access_time = meta.atime();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn atime(&self) -> i64;
    /// Returns the time of the last access to the file in nanoseconds.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let nano_last_access_time = meta.atime_nsec();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn mtime(&self) -> i64;
    /// Returns the time of the last modification of the file in nanoseconds.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let nano_last_modification_time = meta.mtime_nsec();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn ctime(&self) -> i64;
    /// Returns the time of the last status change of the file in nanoseconds.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let nano_last_status_change_time = meta.ctime_nsec();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn blksize(&self) -> u64;
    /// Returns the number of blocks allocated to the file, in 512-byte units.
    ///
    /// Please note that this may be smaller than `st_size / 512` when the file has holes.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::MetadataExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("some_file")?;
    ///     let blocks = meta.blocks();
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn blocks(&self) -> u64;
    #[stable(feature = "metadata_ext", since = "1.1.0")]
    fn attrib(&self) -> u8;
}

#[stable(feature = "metadata_ext", since = "1.1.0")]
impl MetadataExt for fs::Metadata {
    fn dev(&self) -> u64 {
        self.st_dev()
    }
    fn ino(&self) -> u64 {
        self.st_ino()
    }
    fn mode(&self) -> u32 {
        self.st_mode()
    }
    fn nlink(&self) -> u64 {
        self.st_nlink()
    }
    fn uid(&self) -> u32 {
        self.st_uid()
    }
    fn gid(&self) -> u32 {
        self.st_gid()
    }
    fn rdev(&self) -> u64 {
        self.st_rdev()
    }
    fn size(&self) -> u64 {
        self.st_size()
    }
    fn atime(&self) -> i64 {
        self.st_atime()
    }
    fn mtime(&self) -> i64 {
        self.st_mtime()
    }
    fn ctime(&self) -> i64 {
        self.st_ctime()
    }
    fn blksize(&self) -> u64 {
        self.st_blksize()
    }
    fn blocks(&self) -> u64 {
        self.st_blocks()
    }
    fn attrib(&self) -> u8 {
        self.st_attrib()
    }
}

/// Unix-specific extensions for [`fs::FileType`].
///
/// Adds support for special Unix file types such as block/character devices,
/// pipes, and sockets.
#[stable(feature = "file_type_ext", since = "1.5.0")]
pub trait FileTypeExt {
    /// Returns whether this file type is a block device.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::FileTypeExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("block_device_file")?;
    ///     let file_type = meta.file_type();
    ///     assert!(file_type.is_block_device());
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "file_type_ext", since = "1.5.0")]
    fn is_block_device(&self) -> bool;
    /// Returns whether this file type is a char device.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::FileTypeExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("char_device_file")?;
    ///     let file_type = meta.file_type();
    ///     assert!(file_type.is_char_device());
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "file_type_ext", since = "1.5.0")]
    fn is_char_device(&self) -> bool;
    /// Returns whether this file type is a fifo.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::FileTypeExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("fifo_file")?;
    ///     let file_type = meta.file_type();
    ///     assert!(file_type.is_fifo());
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "file_type_ext", since = "1.5.0")]
    fn is_fifo(&self) -> bool;
    /// Returns whether this file type is a socket.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs;
    /// use std::os::unix::fs::FileTypeExt;
    /// use std::io;
    ///
    /// fn main() -> io::Result<()> {
    ///     let meta = fs::metadata("unix.socket")?;
    ///     let file_type = meta.file_type();
    ///     assert!(file_type.is_socket());
    ///     Ok(())
    /// }
    /// ```
    #[stable(feature = "file_type_ext", since = "1.5.0")]
    fn is_socket(&self) -> bool;
}

#[stable(feature = "file_type_ext", since = "1.5.0")]
impl FileTypeExt for fs::FileType {
    fn is_block_device(&self) -> bool {
        self.as_inner().is(libc::S_IFBLK)
    }
    fn is_char_device(&self) -> bool {
        self.as_inner().is(libc::S_IFCHR)
    }
    fn is_fifo(&self) -> bool {
        self.as_inner().is(libc::S_IFIFO)
    }
    fn is_socket(&self) -> bool {
        self.as_inner().is(libc::S_IFSOCK)
    }
}

/// Unix-specific extension methods for [`fs::DirEntry`].
#[stable(feature = "dir_entry_ext", since = "1.1.0")]
pub trait DirEntryExt {
    /// Returns the underlying `d_ino` field in the contained `dirent`
    /// structure.
    ///
    /// # Examples
    ///
    /// ```
    /// use std::fs;
    /// use std::os::unix::fs::DirEntryExt;
    ///
    /// 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(), entry.ino());
    ///         }
    ///     }
    /// }
    /// ```
    #[stable(feature = "dir_entry_ext", since = "1.1.0")]
    fn ino(&self) -> u64;
}

#[stable(feature = "dir_entry_ext", since = "1.1.0")]
impl DirEntryExt for fs::DirEntry {
    fn ino(&self) -> u64 {
        self.as_inner().ino()
    }
}

/// Creates a new symbolic link on the filesystem.
///
/// The `dst` path will be a symbolic link pointing to the `src` path.
///
/// # Examples
///
/// ```no_run
/// use std::os::unix::fs;
///
/// fn main() -> std::io::Result<()> {
///     fs::symlink("a.txt", "b.txt")?;
///     Ok(())
/// }
/// ```
#[stable(feature = "symlink", since = "1.1.0")]
pub fn symlink<P: AsRef<Path>, Q: AsRef<Path>>(src: P, dst: Q) -> io::Result<()> {
    sys::fs::symlink(src.as_ref(), dst.as_ref())
}

/// Unix-specific extensions to [`fs::DirBuilder`].
#[stable(feature = "dir_builder", since = "1.6.0")]
pub trait DirBuilderExt {
    /// Sets the mode to create new directories with. This option defaults to
    /// 0o777.
    ///
    /// # Examples
    ///
    /// ```no_run
    /// use std::fs::DirBuilder;
    /// use std::os::unix::fs::DirBuilderExt;
    ///
    /// let mut builder = DirBuilder::new();
    /// builder.mode(0o755);
    /// ```
    #[stable(feature = "dir_builder", since = "1.6.0")]
    fn mode(&mut self, mode: u32) -> &mut Self;
}

#[stable(feature = "dir_builder", since = "1.6.0")]
impl DirBuilderExt for fs::DirBuilder {
    fn mode(&mut self, mode: u32) -> &mut fs::DirBuilder {
        self.as_inner_mut().set_mode(mode);
        self
    }
}
