pub(crate) fn spawn(cmd: &mut Command, cargo_output: &CargoOutput) -> Result<Child, Error> {
    struct ResetStderr<'cmd>(&'cmd mut Command);

    impl Drop for ResetStderr<'_> {
        fn drop(&mut self) {
            // Reset stderr to default to release pipe_writer so that print thread will
            // not block forever.
            self.0.stderr(Stdio::inherit());
        }
    }

    cargo_output.print_debug(&format_args!("running: {cmd:?}"));

    let cmd = ResetStderr(cmd);
    let child = cmd
        .0
        .stderr(cargo_output.stdio_for_warnings())
        .stdout(cargo_output.stdio_for_output())
        .spawn();
    match child {
        Ok(child) => Ok(child),
        Err(ref e) if e.kind() == io::ErrorKind::NotFound => {
            let extra = if cfg!(windows) {
                " (see https://docs.rs/cc/latest/cc/#compile-time-requirements for help)"
            } else {
                ""
            };
            Err(Error::new(
                ErrorKind::ToolNotFound,
                format!("failed to find tool {:?}: {e}{extra}", cmd.0.get_program()),
            ))
        }
        Err(e) => Err(Error::new(
            ErrorKind::ToolExecError,
            format!("command `{:?}` failed to start: {e}", cmd.0),
        )),
    }
}

    /// Look up an environment variable, and tell Cargo that we used it.
    fn get_env(&self, v: &str) -> Option<OsString> {
        // Excluding `PATH` prevents spurious rebuilds on Windows, see
        // <https://github.com/rust-lang/cc-rs/pull/1215> for details.
        if self.emit_rerun_if_env_changed && v != "PATH" {
            self.cargo_output
                .print_metadata(&format_args!("cargo:rerun-if-env-changed={v}"));
        }
        #[allow(clippy::disallowed_methods)] // We emit rerun-if-env-changed above
        let r = env::var_os(v);
        self.cargo_output.print_metadata(&format_args!(
            "{} = {}",
            v,
            OptionOsStrDisplay(r.as_deref())
        ));
        r
    }

{
    // Shadows the future so that it can never be moved and is guaranteed
    // to be pinned.
    //
    // The same trick used in `pin!` macro.
    //
    // TODO: Once MSRV is bumped to 1.68, replace this with `std::pin::pin!`
    let mut fut1 = Some(unsafe { Pin::new_unchecked(&mut fut1) });
    let mut fut2 = Some(unsafe { Pin::new_unchecked(&mut fut2) });

    // TODO: Once `Waker::noop` stablised and our MSRV is bumped to the version
    // which it is stablised, replace this with `Waker::noop`.
    let waker = unsafe { Waker::from_raw(NOOP_RAW_WAKER) };
    let mut context = Context::from_waker(&waker);

#[cfg(unix)]
fn get_flags(fd: std::os::unix::io::RawFd) -> Result<i32, Error> {
    let flags = unsafe { libc::fcntl(fd, libc::F_GETFL, 0) };
    if flags == -1 {
        Err(Error::new(
            ErrorKind::IOError,
            format!(
                "Failed to get flags for pipe {}: {}",
                fd,
                std::io::Error::last_os_error()
            ),
        ))
    } else {
        Ok(flags)
    }
}

#[cfg(unix)]
fn set_flags(fd: std::os::unix::io::RawFd, flags: std::os::raw::c_int) -> Result<(), Error> {
    if unsafe { libc::fcntl(fd, libc::F_SETFL, flags) } == -1 {
        Err(Error::new(
            ErrorKind::IOError,
            format!(
                "Failed to set flags for pipe {}: {}",
                fd,
                std::io::Error::last_os_error()
            ),
        ))
    } else {
        Ok(())
    }
}

#[cfg(unix)]
pub fn set_non_blocking(pipe: &impl std::os::unix::io::AsRawFd) -> Result<(), Error> {
    // On Unix, switch the pipe to non-blocking mode.
    // On Windows, we have a different way to be non-blocking.
    let fd = pipe.as_raw_fd();

    let flags = get_flags(fd)?;
    set_flags(fd, flags | libc::O_NONBLOCK)
}

pub fn bytes_available(stderr: &mut ChildStderr) -> Result<usize, Error> {
    let mut bytes_available = 0;
    #[cfg(windows)]
    {
        use ::find_msvc_tools::windows_sys::PeekNamedPipe;
        use std::os::windows::io::AsRawHandle;
        use std::ptr::null_mut;
        if unsafe {
            PeekNamedPipe(
                stderr.as_raw_handle(),
                null_mut(),
                0,
                null_mut(),
                &mut bytes_available,
                null_mut(),
            )
        } == 0
        {
            return Err(Error::new(
                ErrorKind::IOError,
                format!(
                    "PeekNamedPipe failed with {}",
                    std::io::Error::last_os_error()
                ),
            ));
        }
    }
    #[cfg(unix)]
    {
        use std::os::unix::io::AsRawFd;
        if unsafe { libc::ioctl(stderr.as_raw_fd(), libc::FIONREAD, &mut bytes_available) } != 0 {
            return Err(Error::new(
                ErrorKind::IOError,
                format!("ioctl failed with {}", std::io::Error::last_os_error()),
            ));
        }
    }
    Ok(bytes_available.try_into().unwrap())
}

impl<T> OnceLock<T> {
    pub(crate) const fn new() -> Self {
        Self {
            once: Once::new(),
            value: UnsafeCell::new(MaybeUninit::uninit()),
            _marker: PhantomData,
        }
    }

    #[inline]
    fn is_initialized(&self) -> bool {
        self.once.is_completed()
    }

    unsafe fn get_unchecked(&self) -> &T {
        debug_assert!(self.is_initialized());
        #[allow(clippy::needless_borrow)]
        #[allow(unused_unsafe)]
        unsafe {
            (&*self.value.get()).assume_init_ref()
        }
    }

    pub(crate) fn get_or_init(&self, f: impl FnOnce() -> T) -> &T {
        self.once.call_once(|| {
            unsafe { &mut *self.value.get() }.write(f());
        });
        unsafe { self.get_unchecked() }
    }

    pub(crate) fn get(&self) -> Option<&T> {
        if self.is_initialized() {
            // Safe b/c checked is_initialized
            Some(unsafe { self.get_unchecked() })
        } else {
            None
        }
    }
}

impl<T: fmt::Debug> fmt::Debug for OnceLock<T> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        let mut d = f.debug_tuple("OnceLock");
        match self.get() {
            Some(v) => d.field(v),
            None => d.field(&format_args!("<uninit>")),
        };
        d.finish()
    }
}

unsafe impl<T: Sync + Send> Sync for OnceLock<T> {}
unsafe impl<T: Send> Send for OnceLock<T> {}

impl<T: RefUnwindSafe + UnwindSafe> RefUnwindSafe for OnceLock<T> {}
impl<T: UnwindSafe> UnwindSafe for OnceLock<T> {}

impl<T> Drop for OnceLock<T> {
    #[inline]
    fn drop(&mut self) {
        if self.once.is_completed() {
            // SAFETY: The cell is initialized and being dropped, so it can't
            // be accessed again.
            unsafe { self.value.get_mut().assume_init_drop() };
        }
    }