Remove sigevent support on Fuchsia

It triggers UB, which the compiler warns about beginning with 1.41.0.
Remove it, due to lack of a Fuchsia maintainer and lack of feedback from
the original Fuchsia porter.

Fixes #1441

CHANGELOG.md

@@ -58,6 +58,8 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 - `nix::sys::signalfd::signalfd` is deprecated.  Use
   `nix::sys::signalfd::SignalFd` instead.
   ([#1938](https://github.com/nix-rust/nix/pull/1938))
+- Removed `SigEvent` support on Fuchsia, where it was unsound.
+  ([#2079](https://github.com/nix-rust/nix/pull/2079))
 
 ## [0.26.2] - 2023-01-18
 

src/sys/signal.rs

@@ -13,7 +13,11 @@ use std::os::unix::io::RawFd;
 use std::ptr;
 use std::str::FromStr;
 
-#[cfg(not(any(target_os = "openbsd", target_os = "redox")))]
+#[cfg(not(any(
+    target_os = "fuchsia",
+    target_os = "openbsd",
+    target_os = "redox"
+)))]
 #[cfg(any(feature = "aio", feature = "signal"))]
 pub use self::sigevent::*;
 
@@ -979,7 +983,7 @@ pub type type_of_thread_id = libc::pid_t;
 // sigval is actually a union of a int and a void*.  But it's never really used
 // as a pointer, because neither libc nor the kernel ever dereference it.  nix
 // therefore presents it as an intptr_t, which is how kevent uses it.
-#[cfg(not(any(target_os = "openbsd", target_os = "redox")))]
+#[cfg(not(any(target_os = "fuchsia", target_os = "openbsd", target_os = "redox")))]
 #[derive(Clone, Copy, Debug, Eq, Hash, PartialEq)]
 pub enum SigevNotify {
     /// No notification will be delivered
@@ -1018,7 +1022,11 @@ pub enum SigevNotify {
 }
 }
 
-#[cfg(not(any(target_os = "openbsd", target_os = "redox")))]
+#[cfg(not(any(
+    target_os = "fuchsia",
+    target_os = "openbsd",
+    target_os = "redox"
+)))]
 #[cfg_attr(docsrs, doc(cfg(all())))]
 mod sigevent {
     feature! {
@@ -1052,9 +1060,6 @@ mod sigevent {
         /// Linux, Solaris, and portable programs should prefer `SIGEV_THREAD_ID` or
         /// `SIGEV_SIGNAL`.  That field is part of a union that shares space with the
         /// more genuinely useful `sigev_notify_thread_id`
-        // Allow invalid_value warning on Fuchsia only.
-        // See https://github.com/nix-rust/nix/issues/1441
-        #[cfg_attr(target_os = "fuchsia", allow(invalid_value))]
         pub fn new(sigev_notify: SigevNotify) -> SigEvent {
             let mut sev = unsafe { mem::MaybeUninit::<libc::sigevent>::zeroed().assume_init() };
             sev.sigev_notify = match sigev_notify {