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    //! Unix-specific extensions to primitives in the `std::process` module.

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

    use crate::ffi::OsStr;
    use crate::io;
    use crate::os::unix::io::{AsRawFd, FromRawFd, IntoRawFd, RawFd};
    use crate::process;
    use crate::sys;
    use crate::sys_common::{AsInner, AsInnerMut, FromInner, IntoInner};

    /// Unix-specific extensions to the [`process::Command`] builder.
    #[stable(feature = "rust1", since = "1.0.0")]
    pub trait CommandExt {
        /// Sets the child process's user ID. This translates to a
        /// `setuid` call in the child process. Failure in the `setuid`
        /// call will cause the spawn to fail.
        #[stable(feature = "rust1", since = "1.0.0")]
        fn uid(
            &mut self,
            #[cfg(not(target_os = "vxworks"))] id: u32,
            #[cfg(target_os = "vxworks")] id: u16,
        ) -> &mut process::Command;

        /// Similar to `uid`, but sets the group ID of the child process. This has
        /// the same semantics as the `uid` field.
        #[stable(feature = "rust1", since = "1.0.0")]
        fn gid(
            &mut self,
            #[cfg(not(target_os = "vxworks"))] id: u32,
            #[cfg(target_os = "vxworks")] id: u16,
        ) -> &mut process::Command;

        /// Schedules a closure to be run just before the `exec` function is
        /// invoked.
        ///
        /// The closure is allowed to return an I/O error whose OS error code will
        /// be communicated back to the parent and returned as an error from when
        /// the spawn was requested.
        ///
        /// Multiple closures can be registered and they will be called in order of
        /// their registration. If a closure returns `Err` then no further closures
        /// will be called and the spawn operation will immediately return with a
        /// failure.
        ///
        /// # Notes and Safety
        ///
        /// This closure will be run in the context of the child process after a
        /// `fork`. This primarily means that any modifications made to memory on
        /// behalf of this closure will **not** be visible to the parent process.
        /// This is often a very constrained environment where normal operations
        /// like `malloc` or acquiring a mutex are not guaranteed to work (due to
        /// other threads perhaps still running when the `fork` was run).
        ///
        /// This also means that all resources such as file descriptors and
        /// memory-mapped regions got duplicated. It is your responsibility to make
        /// sure that the closure does not violate library invariants by making
        /// invalid use of these duplicates.
        ///
        /// When this closure is run, aspects such as the stdio file descriptors and
        /// working directory have successfully been changed, so output to these
        /// locations may not appear where intended.
        #[stable(feature = "process_pre_exec", since = "1.34.0")]
        unsafe fn pre_exec<F>(&mut self, f: F) -> &mut process::Command
        where
            F: FnMut() -> io::Result<()> + Send + Sync + 'static;

        /// Schedules a closure to be run just before the `exec` function is
        /// invoked.
        ///
        /// This method is stable and usable, but it should be unsafe. To fix
        /// that, it got deprecated in favor of the unsafe [`pre_exec`].
        ///
        /// [`pre_exec`]: CommandExt::pre_exec
        #[stable(feature = "process_exec", since = "1.15.0")]
        #[rustc_deprecated(since = "1.37.0", reason = "should be unsafe, use `pre_exec` instead")]
        fn before_exec<F>(&mut self, f: F) -> &mut process::Command
        where
            F: FnMut() -> io::Result<()> + Send + Sync + 'static,
        {
            unsafe { self.pre_exec(f) }
        }

        /// Performs all the required setup by this `Command`, followed by calling
        /// the `execvp` syscall.
        ///
        /// On success this function will not return, and otherwise it will return
        /// an error indicating why the exec (or another part of the setup of the
        /// `Command`) failed.
        ///
        /// `exec` not returning has the same implications as calling
        /// [`process::exit`] – no destructors on the current stack or any other
        /// thread’s stack will be run. Therefore, it is recommended to only call
        /// `exec` at a point where it is fine to not run any destructors. Note,
        /// that the `execvp` syscall independently guarantees that all memory is
        /// freed and all file descriptors with the `CLOEXEC` option (set by default
        /// on all file descriptors opened by the standard library) are closed.
        ///
        /// This function, unlike `spawn`, will **not** `fork` the process to create
        /// a new child. Like spawn, however, the default behavior for the stdio
        /// descriptors will be to inherited from the current process.
        ///
        /// # Notes
        ///
        /// The process may be in a "broken state" if this function returns in
        /// error. For example the working directory, environment variables, signal
        /// handling settings, various user/group information, or aspects of stdio
        /// file descriptors may have changed. If a "transactional spawn" is
        /// required to gracefully handle errors it is recommended to use the
        /// cross-platform `spawn` instead.
        #[stable(feature = "process_exec2", since = "1.9.0")]
        fn exec(&mut self) -> io::Error;

        /// Set executable argument
        ///
        /// Set the first process argument, `argv[0]`, to something other than the
        /// default executable path.
        #[stable(feature = "process_set_argv0", since = "1.45.0")]
        fn arg0<S>(&mut self, arg: S) -> &mut process::Command
        where
            S: AsRef<OsStr>;
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl CommandExt for process::Command {
        fn uid(
            &mut self,
            #[cfg(not(target_os = "vxworks"))] id: u32,
            #[cfg(target_os = "vxworks")] id: u16,
        ) -> &mut process::Command {
            self.as_inner_mut().uid(id);
            self
        }

        fn gid(
            &mut self,
            #[cfg(not(target_os = "vxworks"))] id: u32,
            #[cfg(target_os = "vxworks")] id: u16,
        ) -> &mut process::Command {
            self.as_inner_mut().gid(id);
            self
        }

        unsafe fn pre_exec<F>(&mut self, f: F) -> &mut process::Command
        where
            F: FnMut() -> io::Result<()> + Send + Sync + 'static,
        {
            self.as_inner_mut().pre_exec(Box::new(f));
            self
        }

        fn exec(&mut self) -> io::Error {
            self.as_inner_mut().exec(sys::process::Stdio::Inherit)
        }

        fn arg0<S>(&mut self, arg: S) -> &mut process::Command
        where
            S: AsRef<OsStr>,
        {
            self.as_inner_mut().set_arg_0(arg.as_ref());
            self
        }
    }

    /// Unix-specific extensions to [`process::ExitStatus`].
    #[stable(feature = "rust1", since = "1.0.0")]
    pub trait ExitStatusExt {
        /// Creates a new `ExitStatus` from the raw underlying `i32` return value of
        /// a process.
        #[stable(feature = "exit_status_from", since = "1.12.0")]
        fn from_raw(raw: i32) -> Self;

        /// If the process was terminated by a signal, returns that signal.
        #[stable(feature = "rust1", since = "1.0.0")]
        fn signal(&self) -> Option<i32>;
    }

    #[stable(feature = "rust1", since = "1.0.0")]
    impl ExitStatusExt for process::ExitStatus {
        fn from_raw(raw: i32) -> Self {
            process::ExitStatus::from_inner(From::from(raw))
        }

        fn signal(&self) -> Option<i32> {
            self.as_inner().signal()
        }
    }

    #[stable(feature = "process_extensions", since = "1.2.0")]
    impl FromRawFd for process::Stdio {
        unsafe fn from_raw_fd(fd: RawFd) -> process::Stdio {
            let fd = sys::fd::FileDesc::new(fd);
            let io = sys::process::Stdio::Fd(fd);
            process::Stdio::from_inner(io)
        }
    }

    #[stable(feature = "process_extensions", since = "1.2.0")]
    impl AsRawFd for process::ChildStdin {
        fn as_raw_fd(&self) -> RawFd {
            self.as_inner().fd().raw()
        }
    }

    #[stable(feature = "process_extensions", since = "1.2.0")]
    impl AsRawFd for process::ChildStdout {
        fn as_raw_fd(&self) -> RawFd {
            self.as_inner().fd().raw()
        }
    }

    #[stable(feature = "process_extensions", since = "1.2.0")]
    impl AsRawFd for process::ChildStderr {
        fn as_raw_fd(&self) -> RawFd {
            self.as_inner().fd().raw()
        }
    }

    #[stable(feature = "into_raw_os", since = "1.4.0")]
    impl IntoRawFd for process::ChildStdin {
        fn into_raw_fd(self) -> RawFd {
            self.into_inner().into_fd().into_raw()
        }
    }

    #[stable(feature = "into_raw_os", since = "1.4.0")]
    impl IntoRawFd for process::ChildStdout {
        fn into_raw_fd(self) -> RawFd {
            self.into_inner().into_fd().into_raw()
        }
    }

    #[stable(feature = "into_raw_os", since = "1.4.0")]
    impl IntoRawFd for process::ChildStderr {
        fn into_raw_fd(self) -> RawFd {
            self.into_inner().into_fd().into_raw()
        }
    }

    /// Returns the OS-assigned process identifier associated with this process's parent.
    #[stable(feature = "unix_ppid", since = "1.27.0")]
    pub fn parent_id() -> u32 {
        crate::sys::os::getppid()
    }