Add rustc_nonnull_optimization_guaranteed to Owned/Borrowed Fd/Socket

PR #94586 added support for using
`rustc_nonnull_optimization_guaranteed` on values where the "null" value
is the all-ones bitpattern.

Now that #94586 has made it to the stage0 compiler, add
`rustc_nonnull_optimization_guaranteed` to `OwnedFd`, `BorrowedFd`,
`OwnedSocket`, and `BorrowedSocket`, since these types all exclude
all-ones bitpatterns.

This allows `Option<OwnedFd>`, `Option<BorrowedFd>`, `Option<OwnedSocket>`,
and `Option<BorrowedSocket>` to be used in FFI declarations, as described
in the [I/O safety RFC].

[I/O safety RFC]: https://github.com/rust-lang/rfcs/blob/master/text/3128-io-safety.md#ownedfd-and-borrowedfdfd-1

1 files changed, 2 insertions, 0 deletions

diff --git a/library/std/src/os/windows/io/socket.rs b/library/std/src/os/windows/io/socket.rs
index c14a1d6192f..baae92c19f2 100644
--- a/library/std/src/os/windows/io/socket.rs
+++ b/library/std/src/os/windows/io/socket.rs
@@ -34,6 +34,7 @@ use crate::sys::cvt;
     target_pointer_width = "64",
     rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FF_FF_FF_FF_FE)
 )]
+#[rustc_nonnull_optimization_guaranteed]
 #[unstable(feature = "io_safety", issue = "87074")]
 pub struct BorrowedSocket<'socket> {
     socket: RawSocket,
@@ -56,6 +57,7 @@ pub struct BorrowedSocket<'socket> {
     target_pointer_width = "64",
     rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FF_FF_FF_FF_FE)
 )]
+#[rustc_nonnull_optimization_guaranteed]
 #[unstable(feature = "io_safety", issue = "87074")]
 pub struct OwnedSocket {
     socket: RawSocket,