Sigset conveniance (#1959)

* feat: `impl From<Signal> for SigSet`

* feat: `impl std::ops::BitOr for SigSet`

* feat: `impl std::ops::BitOr for Signal`

* feat: `impl std::ops::BitOr<Signal> for SigSet`

Author: JonathanWoollett-Light

CHANGELOG.md

@@ -11,6 +11,16 @@ This project adheres to [Semantic Versioning](https://semver.org/).
 
 - Fixed the function signature of `recvmmsg`, potentially causing UB
   ([#2119](https://github.com/nix-rust/nix/issues/2119))
+### Added
+
+- Added `impl From<Signal> for SigSet`.
+  ([#1959](https://github.com/nix-rust/nix/pull/1959))
+- Added `impl std::ops::BitOr for SigSet`.
+  ([#1959](https://github.com/nix-rust/nix/pull/1959))
+- Added `impl std::ops::BitOr for Signal`.
+  ([#1959](https://github.com/nix-rust/nix/pull/1959))
+- Added `impl std::ops::BitOr<Signal> for SigSet`
+  ([#1959](https://github.com/nix-rust/nix/pull/1959))
 
 - Fix `SignalFd::set_mask`.  In 0.27.0 it would actually close the file
   descriptor.

src/sys/signal.rs

@@ -9,6 +9,7 @@ use cfg_if::cfg_if;
 use std::fmt;
 use std::hash::{Hash, Hasher};
 use std::mem;
+use std::ops::BitOr;
 #[cfg(any(target_os = "dragonfly", target_os = "freebsd"))]
 use std::os::unix::io::RawFd;
 use std::ptr;
@@ -604,6 +605,42 @@ impl SigSet {
     }
 }
 
+impl From<Signal> for SigSet {
+    fn from(signal: Signal) -> SigSet {
+        let mut sigset = SigSet::empty();
+        sigset.add(signal);
+        sigset
+    }
+}
+
+impl BitOr for Signal {
+    type Output = SigSet;
+
+    fn bitor(self, rhs: Self) -> Self::Output {
+        let mut sigset = SigSet::empty();
+        sigset.add(self);
+        sigset.add(rhs);
+        sigset
+    }
+}
+
+impl BitOr<Signal> for SigSet {
+    type Output = SigSet;
+
+    fn bitor(mut self, rhs: Signal) -> Self::Output {
+        self.add(rhs);
+        self
+    }
+}
+
+impl BitOr for SigSet {
+    type Output = Self;
+
+    fn bitor(self, rhs: Self) -> Self::Output {
+        self.iter().chain(rhs.iter()).collect()
+    }
+}
+
 impl AsRef<libc::sigset_t> for SigSet {
     fn as_ref(&self) -> &libc::sigset_t {
         &self.sigset