Make signal argument to kill optional

CHANGELOG.md

@@ -22,6 +22,12 @@ This project adheres to [Semantic Versioning](http://semver.org/).
   ([#457](https://github.com/nix-rust/nix/pull/457))
 
 ### Changed
+- `kill`'s signature, defined in `::nix::sys::signal`, changed, so that the
+  signal parameter has type `T: Into<Option<Signal>>`. `None` as an argument
+  for that parameter will result in a 0 passed to libc's `kill`, while a
+  `Some`-argument will result in the previous behavior for the contained
+  `Signal`.
+  ([#445](https://github.com/nix-rust/nix/pull/410))
 - The minimum supported version of rustc is now 1.7.0.
   ([#444](https://github.com/nix-rust/nix/pull/444))
 - Implement `Send` for `KEvent`

src/sys/signal.rs

@@ -387,8 +387,12 @@ pub fn pthread_sigmask(how: SigFlags,
     Errno::result(res).map(drop)
 }
 
-pub fn kill(pid: libc::pid_t, signal: Signal) -> Result<()> {
-    let res = unsafe { libc::kill(pid, signal as libc::c_int) };
+pub fn kill<T: Into<Option<Signal>>>(pid: libc::pid_t, signal: T) -> Result<()> {
+    let res = unsafe { libc::kill(pid,
+                                  match signal.into() {
+                                      Some(s) => s as libc::c_int,
+                                      None => 0,
+                                  }) };
 
     Errno::result(res).map(drop)
 }

test/sys/mod.rs

@@ -1,3 +1,4 @@
+mod test_signal;
 mod test_socket;
 mod test_sockopt;
 mod test_termios;

test/sys/test_signal.rs

@@ -0,0 +1,7 @@
+use nix::unistd::*;
+use nix::sys::signal::*;
+
+#[test]
+fn test_kill_none() {
+    kill(getpid(), None).ok().expect("Should be able to send signal to myself.");
+}

test/sys/test_wait.rs

@@ -9,7 +9,7 @@ fn test_wait_signal() {
     match fork() {
       Ok(Child) => pause().unwrap_or(()),
       Ok(Parent { child }) => {
-          kill(child, SIGKILL).ok().expect("Error: Kill Failed");
+          kill(child, Some(SIGKILL)).ok().expect("Error: Kill Failed");
           assert_eq!(waitpid(child, None), Ok(WaitStatus::Signaled(child, SIGKILL, false)));
       },
       // panic, fork should never fail unless there is a serious problem with the OS