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use std::{
    io::{Error, Result},
    os::unix::prelude::*,
};

pub unsafe fn isatty(fd: RawFd) -> Result<bool> {
    let res = libc::isatty(fd);
    if res == 1 {
        // isatty() returns 1 if fd is an open file descriptor referring to a terminal...
        Ok(true)
    } else {
        // ... otherwise 0 is returned, and errno is set to indicate the error.
        let errno = Error::last_os_error();
        let raw_errno = errno.raw_os_error().unwrap();
        // While POSIX specifies ENOTTY if the passed
        // fd is *not* a tty, on Linux, some implementations
        // may return EINVAL instead.
        //
        // https://linux.die.net/man/3/isatty
        if raw_errno == libc::ENOTTY || raw_errno == libc::EINVAL {
            Ok(false)
        } else {
            Err(errno)
        }
    }
}