Auto merge of #87329 - sunfishcode:sunfishcode/io-safety, r=joshtriplett

I/O safety.

Introduce `OwnedFd` and `BorrowedFd`, and the `AsFd` trait, and
implementations of `AsFd`, `From<OwnedFd>` and `From<T> for OwnedFd`
for relevant types, along with Windows counterparts for handles and
sockets.

Tracking issue: <https://github.com/rust-lang/rust/issues/87074>

RFC: <https://github.com/rust-lang/rfcs/blob/master/text/3128-io-safety.md>

Highlights:
 - The doc comments at the top of library/std/src/os/unix/io/mod.rs and library/std/src/os/windows/io/mod.rs
 - The new types and traits in library/std/src/os/unix/io/fd.rs and library/std/src/os/windows/io/handle.rs
 - The removal of the `RawHandle` struct the Windows impl, which had the same name as the `RawHandle` type alias, and its functionality is now folded into `Handle`.

Managing five levels of wrapping (File wraps sys::fs::File wraps sys::fs::FileDesc wraps OwnedFd wraps RawFd, etc.) made for a fair amount of churn and verbose as/into/from sequences in some places. I've managed to simplify some of them, but I'm open to ideas here.

r? `@joshtriplett`

3 files changed, 19 insertions, 2 deletions

diff --git a/library/std/src/net/tcp.rs b/library/std/src/net/tcp.rs
index c8eb4811f7e..336891ec1eb 100644
--- a/library/std/src/net/tcp.rs
+++ b/library/std/src/net/tcp.rs
@@ -546,6 +546,12 @@ impl TcpStream {
     }
 }
 
+// In addition to the `impl`s here, `TcpStream` also has `impl`s for
+// `AsFd`/`From<OwnedFd>`/`Into<OwnedFd>` and
+// `AsRawFd`/`IntoRawFd`/`FromRawFd`, on Unix and WASI, and
+// `AsSocket`/`From<OwnedSocket>`/`Into<OwnedSocket>` and
+// `AsRawSocket`/`IntoRawSocket`/`FromRawSocket` on Windows.
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl Read for TcpStream {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
@@ -915,6 +921,12 @@ impl TcpListener {
     }
 }
 
+// In addition to the `impl`s here, `TcpListener` also has `impl`s for
+// `AsFd`/`From<OwnedFd>`/`Into<OwnedFd>` and
+// `AsRawFd`/`IntoRawFd`/`FromRawFd`, on Unix and WASI, and
+// `AsSocket`/`From<OwnedSocket>`/`Into<OwnedSocket>` and
+// `AsRawSocket`/`IntoRawSocket`/`FromRawSocket` on Windows.
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a> Iterator for Incoming<'a> {
     type Item = io::Result<TcpStream>;
diff --git a/library/std/src/net/udp.rs b/library/std/src/net/udp.rs
index d2088a12b2c..871505843af 100644
--- a/library/std/src/net/udp.rs
+++ b/library/std/src/net/udp.rs
@@ -779,6 +779,12 @@ impl UdpSocket {
     }
 }
 
+// In addition to the `impl`s here, `UdpSocket` also has `impl`s for
+// `AsFd`/`From<OwnedFd>`/`Into<OwnedFd>` and
+// `AsRawFd`/`IntoRawFd`/`FromRawFd`, on Unix and WASI, and
+// `AsSocket`/`From<OwnedSocket>`/`Into<OwnedSocket>` and
+// `AsRawSocket`/`IntoRawSocket`/`FromRawSocket` on Windows.
+
 impl AsInner<net_imp::UdpSocket> for UdpSocket {
     fn as_inner(&self) -> &net_imp::UdpSocket {
         &self.0
diff --git a/library/std/src/net/udp/tests.rs b/library/std/src/net/udp/tests.rs
index fbed3d32d45..a51113dd9e7 100644
--- a/library/std/src/net/udp/tests.rs
+++ b/library/std/src/net/udp/tests.rs
@@ -2,7 +2,6 @@ use crate::io::ErrorKind;
 use crate::net::test::{next_test_ip4, next_test_ip6};
 use crate::net::*;
 use crate::sync::mpsc::channel;
-use crate::sys_common::AsInner;
 use crate::thread;
 use crate::time::{Duration, Instant};
 
@@ -173,7 +172,7 @@ fn debug() {
     let socket_addr = next_test_ip4();
 
     let udpsock = t!(UdpSocket::bind(&socket_addr));
-    let udpsock_inner = udpsock.0.socket().as_inner();
+    let udpsock_inner = udpsock.0.socket().as_raw();
     let compare = format!("UdpSocket {{ addr: {:?}, {}: {:?} }}", socket_addr, name, udpsock_inner);
     assert_eq!(format!("{:?}", udpsock), compare);
 }