Rollup merge of #39512 - oconnor663:try_wait, r=alexcrichton

make Child::try_wait return io::Result<Option<ExitStatus>>

This is much nicer for callers who want to short-circuit real I/O errors
with `?`, because they can write this

    if let Some(status) = foo.try_wait()? {
        ...
    } else {
        ...
    }

instead of this

    match foo.try_wait() {
        Ok(status) => {
            ...
        }
        Err(err) if err.kind() == io::ErrorKind::WouldBlock => {
            ...
        }
        Err(err) => return Err(err),
    }

The original design of `try_wait` was patterned after the `Read` and
`Write` traits, which support both blocking and non-blocking
implementations in a single API. But since `try_wait` is never blocking,
it makes sense to optimize for the non-blocking case.

Tracking issue: https://github.com/rust-lang/rust/issues/38903

1 files changed, 9 insertions, 10 deletions

diff --git a/src/test/run-pass/try-wait.rs b/src/test/run-pass/try-wait.rs
index d9826373cce..be87b7b3c87 100644
--- a/src/test/run-pass/try-wait.rs
+++ b/src/test/run-pass/try-wait.rs
@@ -13,7 +13,6 @@
 #![feature(process_try_wait)]
 
 use std::env;
-use std::io;
 use std::process::Command;
 use std::thread;
 use std::time::Duration;
@@ -32,17 +31,17 @@ fn main() {
                          .arg("sleep")
                          .spawn()
                          .unwrap();
-    let err = me.try_wait().unwrap_err();
-    assert_eq!(err.kind(), io::ErrorKind::WouldBlock);
-    let err = me.try_wait().unwrap_err();
-    assert_eq!(err.kind(), io::ErrorKind::WouldBlock);
+    let maybe_status = me.try_wait().unwrap();
+    assert!(maybe_status.is_none());
+    let maybe_status = me.try_wait().unwrap();
+    assert!(maybe_status.is_none());
 
     me.kill().unwrap();
     me.wait().unwrap();
 
-    let status = me.try_wait().unwrap();
+    let status = me.try_wait().unwrap().unwrap();
     assert!(!status.success());
-    let status = me.try_wait().unwrap();
+    let status = me.try_wait().unwrap().unwrap();
     assert!(!status.success());
 
     let mut me = Command::new(env::current_exe().unwrap())
@@ -51,17 +50,17 @@ fn main() {
                          .unwrap();
     loop {
         match me.try_wait() {
-            Ok(res) => {
+            Ok(Some(res)) => {
                 assert!(res.success());
                 break
             }
-            Err(ref e) if e.kind() == io::ErrorKind::WouldBlock => {
+            Ok(None) => {
                 thread::sleep(Duration::from_millis(1));
             }
             Err(e) => panic!("error in try_wait: {}", e),
         }
     }
 
-    let status = me.try_wait().unwrap();
+    let status = me.try_wait().unwrap().unwrap();
     assert!(status.success());
 }