Add `IsTerminal` trait to determine if a descriptor or handle is a terminal

The UNIX and WASI implementations use `isatty`. The Windows
implementation uses the same logic the `atty` crate uses, including the
hack needed to detect msys terminals.

Implement this trait for `File` and for `Stdin`/`Stdout`/`Stderr` and
their locked counterparts on all platforms. On UNIX and WASI, implement
it for `BorrowedFd`/`OwnedFd`. On Windows, implement it for
`BorrowedHandle`/`OwnedHandle`.

Based on https://github.com/rust-lang/rust/pull/91121

Co-authored-by: Matt Wilkinson <mattwilki17@gmail.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/library/std/src/sys/unix/io.rs b/library/std/src/sys/unix/io.rs
index deb5ee76bd0..29c340dd349 100644
--- a/library/std/src/sys/unix/io.rs
+++ b/library/std/src/sys/unix/io.rs
@@ -1,4 +1,5 @@
 use crate::marker::PhantomData;
+use crate::os::fd::{AsFd, AsRawFd};
 use crate::slice;
 
 use libc::{c_void, iovec};
@@ -74,3 +75,8 @@ impl<'a> IoSliceMut<'a> {
         unsafe { slice::from_raw_parts_mut(self.vec.iov_base as *mut u8, self.vec.iov_len) }
     }
 }
+
+pub fn is_terminal(fd: &impl AsFd) -> bool {
+    let fd = fd.as_fd();
+    unsafe { libc::isatty(fd.as_raw_fd()) != 0 }
+}