Auto merge of #39563 - frewsxcv:rollup, r=frewsxcv

Rollup of 19 pull requests

- Successful merges: #38518, #38921, #38959, #38983, #39009, #39107, #39193, #39289, #39312, #39393, #39442, #39443, #39453, #39454, #39471, #39477, #39478, #39527, #39552
- Failed merges:

28 files changed, 352 insertions, 72 deletions

diff --git a/src/libstd/ascii.rs b/src/libstd/ascii.rs
index b220504d2b4..35c388ba076 100644
--- a/src/libstd/ascii.rs
+++ b/src/libstd/ascii.rs
@@ -399,7 +399,7 @@ impl ExactSizeIterator for EscapeDefault {}
 #[unstable(feature = "fused", issue = "35602")]
 impl FusedIterator for EscapeDefault {}
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for EscapeDefault {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("EscapeDefault { .. }")
diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs
index 8058972e750..ffb7a1a1fc1 100644
--- a/src/libstd/collections/hash/map.rs
+++ b/src/libstd/collections/hash/map.rs
@@ -1283,7 +1283,7 @@ impl<'a, K, V> Clone for Iter<'a, K, V> {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, K: Debug, V: Debug> fmt::Debug for Iter<'a, K, V> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_list()
@@ -1318,7 +1318,7 @@ impl<'a, K, V> Clone for Keys<'a, K, V> {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, K: Debug, V: Debug> fmt::Debug for Keys<'a, K, V> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_list()
@@ -1341,7 +1341,7 @@ impl<'a, K, V> Clone for Values<'a, K, V> {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, K: Debug, V: Debug> fmt::Debug for Values<'a, K, V> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_list()
@@ -1591,7 +1591,7 @@ impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, K, V> FusedIterator for IterMut<'a, K, V> {}
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, K, V> fmt::Debug for IterMut<'a, K, V>
     where K: fmt::Debug,
           V: fmt::Debug,
@@ -1626,7 +1626,7 @@ impl<K, V> ExactSizeIterator for IntoIter<K, V> {
 #[unstable(feature = "fused", issue = "35602")]
 impl<K, V> FusedIterator for IntoIter<K, V> {}
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<K: Debug, V: Debug> fmt::Debug for IntoIter<K, V> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_list()
@@ -1704,7 +1704,7 @@ impl<'a, K, V> ExactSizeIterator for ValuesMut<'a, K, V> {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, K, V> FusedIterator for ValuesMut<'a, K, V> {}
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, K, V> fmt::Debug for ValuesMut<'a, K, V>
     where K: fmt::Debug,
           V: fmt::Debug,
@@ -1739,7 +1739,7 @@ impl<'a, K, V> ExactSizeIterator for Drain<'a, K, V> {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, K, V> FusedIterator for Drain<'a, K, V> {}
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, K, V> fmt::Debug for Drain<'a, K, V>
     where K: fmt::Debug,
           V: fmt::Debug,
@@ -2227,7 +2227,7 @@ impl Default for RandomState {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for RandomState {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("RandomState { .. }")
diff --git a/src/libstd/collections/hash/set.rs b/src/libstd/collections/hash/set.rs
index 341b050862f..a3f7e13bbf9 100644
--- a/src/libstd/collections/hash/set.rs
+++ b/src/libstd/collections/hash/set.rs
@@ -948,7 +948,7 @@ impl<'a, K> ExactSizeIterator for Iter<'a, K> {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, K> FusedIterator for Iter<'a, K> {}
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, K: fmt::Debug> fmt::Debug for Iter<'a, K> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_list()
@@ -977,7 +977,7 @@ impl<K> ExactSizeIterator for IntoIter<K> {
 #[unstable(feature = "fused", issue = "35602")]
 impl<K> FusedIterator for IntoIter<K> {}
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<K: fmt::Debug> fmt::Debug for IntoIter<K> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let entries_iter = self.iter.inner.iter().map(|(k, _)| k);
@@ -1007,7 +1007,7 @@ impl<'a, K> ExactSizeIterator for Drain<'a, K> {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a, K> FusedIterator for Drain<'a, K> {}
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, K: fmt::Debug> fmt::Debug for Drain<'a, K> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         let entries_iter = self.iter.inner.iter().map(|(k, _)| k);
@@ -1050,7 +1050,7 @@ impl<'a, T, S> Iterator for Intersection<'a, T, S>
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, T, S> fmt::Debug for Intersection<'a, T, S>
     where T: fmt::Debug + Eq + Hash,
           S: BuildHasher,
@@ -1109,7 +1109,7 @@ impl<'a, T, S> FusedIterator for Difference<'a, T, S>
 {
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, T, S> fmt::Debug for Difference<'a, T, S>
     where T: fmt::Debug + Eq + Hash,
           S: BuildHasher,
@@ -1150,7 +1150,7 @@ impl<'a, T, S> FusedIterator for SymmetricDifference<'a, T, S>
 {
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, T, S> fmt::Debug for SymmetricDifference<'a, T, S>
     where T: fmt::Debug + Eq + Hash,
           S: BuildHasher,
@@ -1176,7 +1176,7 @@ impl<'a, T, S> FusedIterator for Union<'a, T, S>
 {
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, T, S> fmt::Debug for Union<'a, T, S>
     where T: fmt::Debug + Eq + Hash,
           S: BuildHasher,
diff --git a/src/libstd/env.rs b/src/libstd/env.rs
index c3a6b2433ed..29f2ac6ab44 100644
--- a/src/libstd/env.rs
+++ b/src/libstd/env.rs
@@ -145,7 +145,7 @@ impl Iterator for Vars {
     fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Vars {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Vars { .. }")
@@ -159,7 +159,7 @@ impl Iterator for VarsOs {
     fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for VarsOs {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("VarsOs { .. }")
@@ -382,7 +382,7 @@ impl<'a> Iterator for SplitPaths<'a> {
     fn size_hint(&self) -> (usize, Option<usize>) { self.inner.size_hint() }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a> fmt::Debug for SplitPaths<'a> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("SplitPaths { .. }")
@@ -665,7 +665,7 @@ impl DoubleEndedIterator for Args {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Args {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Args { .. }")
@@ -690,7 +690,7 @@ impl DoubleEndedIterator for ArgsOs {
     fn next_back(&mut self) -> Option<OsString> { self.inner.next_back() }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for ArgsOs {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("ArgsOs { .. }")
diff --git a/src/libstd/fs.rs b/src/libstd/fs.rs
index 249627c430c..e5562d05f10 100644
--- a/src/libstd/fs.rs
+++ b/src/libstd/fs.rs
@@ -869,7 +869,7 @@ impl Metadata {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Metadata {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("Metadata")
diff --git a/src/libstd/io/mod.rs b/src/libstd/io/mod.rs
index de5fc5bfad1..8cb7b2bda75 100644
--- a/src/libstd/io/mod.rs
+++ b/src/libstd/io/mod.rs
@@ -1450,7 +1450,7 @@ pub struct Chain<T, U> {
     done_first: bool,
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<T: fmt::Debug, U: fmt::Debug> fmt::Debug for Chain<T, U> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("Chain")
diff --git a/src/libstd/io/stdio.rs b/src/libstd/io/stdio.rs
index 83a675eb512..e16e8019b5f 100644
--- a/src/libstd/io/stdio.rs
+++ b/src/libstd/io/stdio.rs
@@ -282,7 +282,7 @@ impl Stdin {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Stdin {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Stdin { .. }")
@@ -321,7 +321,7 @@ impl<'a> BufRead for StdinLock<'a> {
     fn consume(&mut self, n: usize) { self.inner.consume(n) }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a> fmt::Debug for StdinLock<'a> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("StdinLock { .. }")
@@ -438,7 +438,7 @@ impl Stdout {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Stdout {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Stdout { .. }")
@@ -470,7 +470,7 @@ impl<'a> Write for StdoutLock<'a> {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a> fmt::Debug for StdoutLock<'a> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("StdoutLock { .. }")
@@ -573,7 +573,7 @@ impl Stderr {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Stderr {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Stderr { .. }")
@@ -605,7 +605,7 @@ impl<'a> Write for StderrLock<'a> {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a> fmt::Debug for StderrLock<'a> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("StderrLock { .. }")
diff --git a/src/libstd/io/util.rs b/src/libstd/io/util.rs
index e50665120eb..4163187488e 100644
--- a/src/libstd/io/util.rs
+++ b/src/libstd/io/util.rs
@@ -98,7 +98,7 @@ impl BufRead for Empty {
     fn consume(&mut self, _n: usize) {}
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Empty {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Empty { .. }")
@@ -141,7 +141,7 @@ impl Read for Repeat {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Repeat {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Repeat { .. }")
@@ -180,7 +180,7 @@ impl Write for Sink {
     fn flush(&mut self) -> io::Result<()> { Ok(()) }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Sink {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Sink { .. }")
diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 181694dead0..9bcecebf693 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -277,6 +277,7 @@
 #![feature(oom)]
 #![feature(optin_builtin_traits)]
 #![feature(panic_unwind)]
+#![feature(peek)]
 #![feature(placement_in_syntax)]
 #![feature(prelude_import)]
 #![feature(pub_restricted)]
diff --git a/src/libstd/net/mod.rs b/src/libstd/net/mod.rs
index 2b60fc38198..b0d2e3e4687 100644
--- a/src/libstd/net/mod.rs
+++ b/src/libstd/net/mod.rs
@@ -106,7 +106,10 @@ impl Iterator for LookupHost {
     fn next(&mut self) -> Option<SocketAddr> { self.0.next() }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[unstable(feature = "lookup_host", reason = "unsure about the returned \
+                                              iterator and returning socket \
+                                              addresses",
+           issue = "27705")]
 impl fmt::Debug for LookupHost {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("LookupHost { .. }")
diff --git a/src/libstd/net/tcp.rs b/src/libstd/net/tcp.rs
index cbc672c28bc..9bead22ef7f 100644
--- a/src/libstd/net/tcp.rs
+++ b/src/libstd/net/tcp.rs
@@ -296,6 +296,29 @@ impl TcpStream {
         self.0.write_timeout()
     }
 
+    /// Receives data on the socket from the remote adress to which it is
+    /// connected, without removing that data from the queue. On success,
+    /// returns the number of bytes peeked.
+    ///
+    /// Successive calls return the same data. This is accomplished by passing
+    /// `MSG_PEEK` as a flag to the underlying `recv` system call.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// #![feature(peek)]
+    /// use std::net::TcpStream;
+    ///
+    /// let stream = TcpStream::connect("127.0.0.1:8000")
+    ///                        .expect("couldn't bind to address");
+    /// let mut buf = [0; 10];
+    /// let len = stream.peek(&mut buf).expect("peek failed");
+    /// ```
+    #[unstable(feature = "peek", issue = "38980")]
+    pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.0.peek(buf)
+    }
+
     /// Sets the value of the `TCP_NODELAY` option on this socket.
     ///
     /// If set, this option disables the Nagle algorithm. This means that
@@ -1406,4 +1429,35 @@ mod tests {
             Err(e) => panic!("unexpected error {}", e),
         }
     }
+
+    #[test]
+    fn peek() {
+        each_ip(&mut |addr| {
+            let (txdone, rxdone) = channel();
+
+            let srv = t!(TcpListener::bind(&addr));
+            let _t = thread::spawn(move|| {
+                let mut cl = t!(srv.accept()).0;
+                cl.write(&[1,3,3,7]).unwrap();
+                t!(rxdone.recv());
+            });
+
+            let mut c = t!(TcpStream::connect(&addr));
+            let mut b = [0; 10];
+            for _ in 1..3 {
+                let len = c.peek(&mut b).unwrap();
+                assert_eq!(len, 4);
+            }
+            let len = c.read(&mut b).unwrap();
+            assert_eq!(len, 4);
+
+            t!(c.set_nonblocking(true));
+            match c.peek(&mut b) {
+                Ok(_) => panic!("expected error"),
+                Err(ref e) if e.kind() == ErrorKind::WouldBlock => {}
+                Err(e) => panic!("unexpected error {}", e),
+            }
+            t!(txdone.send(()));
+        })
+    }
 }
diff --git a/src/libstd/net/udp.rs b/src/libstd/net/udp.rs
index 492e57f6e44..f452c75d389 100644
--- a/src/libstd/net/udp.rs
+++ b/src/libstd/net/udp.rs
@@ -83,6 +83,30 @@ impl UdpSocket {
         self.0.recv_from(buf)
     }
 
+    /// Receives data from the socket, without removing it from the queue.
+    ///
+    /// Successive calls return the same data. This is accomplished by passing
+    /// `MSG_PEEK` as a flag to the underlying `recvfrom` system call.
+    ///
+    /// On success, returns the number of bytes peeked and the address from
+    /// whence the data came.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// #![feature(peek)]
+    /// use std::net::UdpSocket;
+    ///
+    /// let socket = UdpSocket::bind("127.0.0.1:34254").expect("couldn't bind to address");
+    /// let mut buf = [0; 10];
+    /// let (number_of_bytes, src_addr) = socket.peek_from(&mut buf)
+    ///                                         .expect("Didn't receive data");
+    /// ```
+    #[unstable(feature = "peek", issue = "38980")]
+    pub fn peek_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.0.peek_from(buf)
+    }
+
     /// Sends data on the socket to the given address. On success, returns the
     /// number of bytes written.
     ///
@@ -579,6 +603,37 @@ impl UdpSocket {
         self.0.recv(buf)
     }
 
+    /// Receives data on the socket from the remote adress to which it is
+    /// connected, without removing that data from the queue. On success,
+    /// returns the number of bytes peeked.
+    ///
+    /// Successive calls return the same data. This is accomplished by passing
+    /// `MSG_PEEK` as a flag to the underlying `recv` system call.
+    ///
+    /// # Errors
+    ///
+    /// This method will fail if the socket is not connected. The `connect` method
+    /// will connect this socket to a remote address.
+    ///
+    /// # Examples
+    ///
+    /// ```no_run
+    /// #![feature(peek)]
+    /// use std::net::UdpSocket;
+    ///
+    /// let socket = UdpSocket::bind("127.0.0.1:34254").expect("couldn't bind to address");
+    /// socket.connect("127.0.0.1:8080").expect("connect function failed");
+    /// let mut buf = [0; 10];
+    /// match socket.peek(&mut buf) {
+    ///     Ok(received) => println!("received {} bytes", received),
+    ///     Err(e) => println!("peek function failed: {:?}", e),
+    /// }
+    /// ```
+    #[unstable(feature = "peek", issue = "38980")]
+    pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.0.peek(buf)
+    }
+
     /// Moves this UDP socket into or out of nonblocking mode.
     ///
     /// On Unix this corresponds to calling fcntl, and on Windows this
@@ -870,6 +925,48 @@ mod tests {
     }
 
     #[test]
+    fn connect_send_peek_recv() {
+        each_ip(&mut |addr, _| {
+            let socket = t!(UdpSocket::bind(&addr));
+            t!(socket.connect(addr));
+
+            t!(socket.send(b"hello world"));
+
+            for _ in 1..3 {
+                let mut buf = [0; 11];
+                let size = t!(socket.peek(&mut buf));
+                assert_eq!(b"hello world", &buf[..]);
+                assert_eq!(size, 11);
+            }
+
+            let mut buf = [0; 11];
+            let size = t!(socket.recv(&mut buf));
+            assert_eq!(b"hello world", &buf[..]);
+            assert_eq!(size, 11);
+        })
+    }
+
+    #[test]
+    fn peek_from() {
+        each_ip(&mut |addr, _| {
+            let socket = t!(UdpSocket::bind(&addr));
+            t!(socket.send_to(b"hello world", &addr));
+
+            for _ in 1..3 {
+                let mut buf = [0; 11];
+                let (size, _) = t!(socket.peek_from(&mut buf));
+                assert_eq!(b"hello world", &buf[..]);
+                assert_eq!(size, 11);
+            }
+
+            let mut buf = [0; 11];
+            let (size, _) = t!(socket.recv_from(&mut buf));
+            assert_eq!(b"hello world", &buf[..]);
+            assert_eq!(size, 11);
+        })
+    }
+
+    #[test]
     fn ttl() {
         let ttl = 100;
 
diff --git a/src/libstd/os/raw.rs b/src/libstd/os/raw.rs
index cc154f7ab41..68d4ca90019 100644
--- a/src/libstd/os/raw.rs
+++ b/src/libstd/os/raw.rs
@@ -73,7 +73,7 @@ pub enum c_void {
     #[doc(hidden)] __variant2,
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for c_void {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("c_void")
diff --git a/src/libstd/panic.rs b/src/libstd/panic.rs
index faf4949e861..ac0d0d2afb8 100644
--- a/src/libstd/panic.rs
+++ b/src/libstd/panic.rs
@@ -297,7 +297,7 @@ impl<R, F: FnOnce() -> R> FnOnce<()> for AssertUnwindSafe<F> {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<T: fmt::Debug> fmt::Debug for AssertUnwindSafe<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_tuple("AssertUnwindSafe")
diff --git a/src/libstd/process.rs b/src/libstd/process.rs
index 5af4ba53bf9..c16b97ebda5 100644
--- a/src/libstd/process.rs
+++ b/src/libstd/process.rs
@@ -114,7 +114,7 @@ impl IntoInner<imp::Process> for Child {
     fn into_inner(self) -> imp::Process { self.handle }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Child {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("Child")
@@ -160,7 +160,7 @@ impl FromInner<AnonPipe> for ChildStdin {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for ChildStdin {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("ChildStdin { .. }")
@@ -201,7 +201,7 @@ impl FromInner<AnonPipe> for ChildStdout {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for ChildStdout {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("ChildStdout { .. }")
@@ -242,7 +242,7 @@ impl FromInner<AnonPipe> for ChildStderr {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for ChildStderr {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("ChildStderr { .. }")
@@ -696,7 +696,7 @@ impl FromInner<imp::Stdio> for Stdio {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Stdio {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Stdio { .. }")
@@ -959,10 +959,27 @@ impl Child {
 ///
 /// # Examples
 ///
+/// Due to this function’s behavior regarding destructors, a conventional way
+/// to use the function is to extract the actual computation to another
+/// function and compute the exit code from its return value:
+///
 /// ```
-/// use std::process;
+/// use std::io::{self, Write};
+///
+/// fn run_app() -> Result<(), ()> {
+///     // Application logic here
+///     Ok(())
+/// }
 ///
-/// process::exit(0);
+/// fn main() {
+///     ::std::process::exit(match run_app() {
+///        Ok(_) => 0,
+///        Err(err) => {
+///            writeln!(io::stderr(), "error: {:?}", err).unwrap();
+///            1
+///        }
+///     });
+/// }
 /// ```
 ///
 /// Due to [platform-specific behavior], the exit code for this example will be
diff --git a/src/libstd/sync/barrier.rs b/src/libstd/sync/barrier.rs
index b8e83dced8d..fc4fd4ce92b 100644
--- a/src/libstd/sync/barrier.rs
+++ b/src/libstd/sync/barrier.rs
@@ -55,7 +55,7 @@ struct BarrierState {
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct BarrierWaitResult(bool);
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Barrier {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Barrier { .. }")
@@ -110,7 +110,7 @@ impl Barrier {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for BarrierWaitResult {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("BarrierWaitResult")
diff --git a/src/libstd/sync/condvar.rs b/src/libstd/sync/condvar.rs
index 5c85c4879a8..7ee1c98565c 100644
--- a/src/libstd/sync/condvar.rs
+++ b/src/libstd/sync/condvar.rs
@@ -240,7 +240,7 @@ impl Condvar {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Condvar {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Condvar { .. }")
diff --git a/src/libstd/sync/mutex.rs b/src/libstd/sync/mutex.rs
index 2efddeb4610..0d6ad5e38e9 100644
--- a/src/libstd/sync/mutex.rs
+++ b/src/libstd/sync/mutex.rs
@@ -428,7 +428,7 @@ impl<'a, T: ?Sized> Drop for MutexGuard<'a, T> {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, T: ?Sized + fmt::Debug> fmt::Debug for MutexGuard<'a, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("MutexGuard")
diff --git a/src/libstd/sync/once.rs b/src/libstd/sync/once.rs
index a9747639aac..ba993751391 100644
--- a/src/libstd/sync/once.rs
+++ b/src/libstd/sync/once.rs
@@ -330,7 +330,7 @@ impl Once {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl fmt::Debug for Once {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("Once { .. }")
diff --git a/src/libstd/sync/rwlock.rs b/src/libstd/sync/rwlock.rs
index adbb98e4b1f..a3db0adeda0 100644
--- a/src/libstd/sync/rwlock.rs
+++ b/src/libstd/sync/rwlock.rs
@@ -361,7 +361,7 @@ impl<'rwlock, T: ?Sized> RwLockWriteGuard<'rwlock, T> {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, T: fmt::Debug> fmt::Debug for RwLockReadGuard<'a, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("RwLockReadGuard")
@@ -370,7 +370,7 @@ impl<'a, T: fmt::Debug> fmt::Debug for RwLockReadGuard<'a, T> {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<'a, T: fmt::Debug> fmt::Debug for RwLockWriteGuard<'a, T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.debug_struct("RwLockWriteGuard")
diff --git a/src/libstd/sys/unix/ext/process.rs b/src/libstd/sys/unix/ext/process.rs
index 585dcbb9a34..2961c4ec582 100644
--- a/src/libstd/sys/unix/ext/process.rs
+++ b/src/libstd/sys/unix/ext/process.rs
@@ -67,10 +67,20 @@ pub trait CommandExt {
     /// an error indicating why the exec (or another part of the setup of the
     /// `Command`) failed.
     ///
+    /// `exec` not returning has the same implications as calling
+    /// [`process::exit`] – no destructors on the current stack or any other
+    /// thread’s stack will be run. Therefore, it is recommended to only call
+    /// `exec` at a point where it is fine to not run any destructors. Note,
+    /// that the `execvp` syscall independently guarantees that all memory is
+    /// freed and all file descriptors with the `CLOEXEC` option (set by default
+    /// on all file descriptors opened by the standard library) are closed.
+    ///
     /// This function, unlike `spawn`, will **not** `fork` the process to create
     /// a new child. Like spawn, however, the default behavior for the stdio
     /// descriptors will be to inherited from the current process.
     ///
+    /// [`process::exit`]: ../../../process/fn.exit.html
+    ///
     /// # Notes
     ///
     /// The process may be in a "broken state" if this function returns in
diff --git a/src/libstd/sys/unix/net.rs b/src/libstd/sys/unix/net.rs
index ad287bbec38..5efddca110f 100644
--- a/src/libstd/sys/unix/net.rs
+++ b/src/libstd/sys/unix/net.rs
@@ -10,12 +10,13 @@
 
 use ffi::CStr;
 use io;
-use libc::{self, c_int, size_t, sockaddr, socklen_t, EAI_SYSTEM};
+use libc::{self, c_int, c_void, size_t, sockaddr, socklen_t, EAI_SYSTEM, MSG_PEEK};
+use mem;
 use net::{SocketAddr, Shutdown};
 use str;
 use sys::fd::FileDesc;
 use sys_common::{AsInner, FromInner, IntoInner};
-use sys_common::net::{getsockopt, setsockopt};
+use sys_common::net::{getsockopt, setsockopt, sockaddr_to_addr};
 use time::Duration;
 
 pub use sys::{cvt, cvt_r};
@@ -155,8 +156,46 @@ impl Socket {
         self.0.duplicate().map(Socket)
     }
 
+    fn recv_with_flags(&self, buf: &mut [u8], flags: c_int) -> io::Result<usize> {
+        let ret = cvt(unsafe {
+            libc::recv(self.0.raw(),
+                       buf.as_mut_ptr() as *mut c_void,
+                       buf.len(),
+                       flags)
+        })?;
+        Ok(ret as usize)
+    }
+
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
-        self.0.read(buf)
+        self.recv_with_flags(buf, 0)
+    }
+
+    pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.recv_with_flags(buf, MSG_PEEK)
+    }
+
+    fn recv_from_with_flags(&self, buf: &mut [u8], flags: c_int)
+                            -> io::Result<(usize, SocketAddr)> {
+        let mut storage: libc::sockaddr_storage = unsafe { mem::zeroed() };
+        let mut addrlen = mem::size_of_val(&storage) as libc::socklen_t;
+
+        let n = cvt(unsafe {
+            libc::recvfrom(self.0.raw(),
+                        buf.as_mut_ptr() as *mut c_void,
+                        buf.len(),
+                        flags,
+                        &mut storage as *mut _ as *mut _,
+                        &mut addrlen)
+        })?;
+        Ok((n as usize, sockaddr_to_addr(&storage, addrlen as usize)?))
+    }
+
+    pub fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.recv_from_with_flags(buf, 0)
+    }
+
+    pub fn peek_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.recv_from_with_flags(buf, MSG_PEEK)
     }
 
     pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
diff --git a/src/libstd/sys/windows/c.rs b/src/libstd/sys/windows/c.rs
index 1b29bf73c7a..850d6f49612 100644
--- a/src/libstd/sys/windows/c.rs
+++ b/src/libstd/sys/windows/c.rs
@@ -167,6 +167,7 @@ pub const SYMLINK_FLAG_RELATIVE: DWORD = 0x00000001;
 pub const FSCTL_SET_REPARSE_POINT: DWORD = 0x900a4;
 
 pub const SYMBOLIC_LINK_FLAG_DIRECTORY: DWORD = 0x1;
+pub const SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE: DWORD = 0x2;
 
 // Note that these are not actually HANDLEs, just values to pass to GetStdHandle
 pub const STD_INPUT_HANDLE: DWORD = -10i32 as DWORD;
@@ -245,6 +246,7 @@ pub const IP_ADD_MEMBERSHIP: c_int = 12;
 pub const IP_DROP_MEMBERSHIP: c_int = 13;
 pub const IPV6_ADD_MEMBERSHIP: c_int = 12;
 pub const IPV6_DROP_MEMBERSHIP: c_int = 13;
+pub const MSG_PEEK: c_int = 0x2;
 
 #[repr(C)]
 pub struct ip_mreq {
diff --git a/src/libstd/sys/windows/fs.rs b/src/libstd/sys/windows/fs.rs
index c410fcd1ee0..4efc68afdc4 100644
--- a/src/libstd/sys/windows/fs.rs
+++ b/src/libstd/sys/windows/fs.rs
@@ -646,9 +646,25 @@ pub fn symlink_inner(src: &Path, dst: &Path, dir: bool) -> io::Result<()> {
     let src = to_u16s(src)?;
     let dst = to_u16s(dst)?;
     let flags = if dir { c::SYMBOLIC_LINK_FLAG_DIRECTORY } else { 0 };
-    cvt(unsafe {
-        c::CreateSymbolicLinkW(dst.as_ptr(), src.as_ptr(), flags) as c::BOOL
-    })?;
+    // Formerly, symlink creation required the SeCreateSymbolicLink privilege. For the Windows 10
+    // Creators Update, Microsoft loosened this to allow unprivileged symlink creation if the
+    // computer is in Developer Mode, but SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE must be
+    // added to dwFlags to opt into this behaviour.
+    let result = cvt(unsafe {
+        c::CreateSymbolicLinkW(dst.as_ptr(), src.as_ptr(),
+                               flags | c::SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE) as c::BOOL
+    });
+    if let Err(err) = result {
+        if err.raw_os_error() == Some(c::ERROR_INVALID_PARAMETER as i32) {
+            // Older Windows objects to SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE,
+            // so if we encounter ERROR_INVALID_PARAMETER, retry without that flag.
+            cvt(unsafe {
+                c::CreateSymbolicLinkW(dst.as_ptr(), src.as_ptr(), flags) as c::BOOL
+            })?;
+        } else {
+            return Err(err);
+        }
+    }
     Ok(())
 }
 
diff --git a/src/libstd/sys/windows/net.rs b/src/libstd/sys/windows/net.rs
index aca6994503f..adf6210d82e 100644
--- a/src/libstd/sys/windows/net.rs
+++ b/src/libstd/sys/windows/net.rs
@@ -147,12 +147,12 @@ impl Socket {
         Ok(socket)
     }
 
-    pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
+    fn recv_with_flags(&self, buf: &mut [u8], flags: c_int) -> io::Result<usize> {
         // On unix when a socket is shut down all further reads return 0, so we
         // do the same on windows to map a shut down socket to returning EOF.
         let len = cmp::min(buf.len(), i32::max_value() as usize) as i32;
         unsafe {
-            match c::recv(self.0, buf.as_mut_ptr() as *mut c_void, len, 0) {
+            match c::recv(self.0, buf.as_mut_ptr() as *mut c_void, len, flags) {
                 -1 if c::WSAGetLastError() == c::WSAESHUTDOWN => Ok(0),
                 -1 => Err(last_error()),
                 n => Ok(n as usize)
@@ -160,6 +160,46 @@ impl Socket {
         }
     }
 
+    pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.recv_with_flags(buf, 0)
+    }
+
+    pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.recv_with_flags(buf, c::MSG_PEEK)
+    }
+
+    fn recv_from_with_flags(&self, buf: &mut [u8], flags: c_int)
+                            -> io::Result<(usize, SocketAddr)> {
+        let mut storage: c::SOCKADDR_STORAGE_LH = unsafe { mem::zeroed() };
+        let mut addrlen = mem::size_of_val(&storage) as c::socklen_t;
+        let len = cmp::min(buf.len(), <wrlen_t>::max_value() as usize) as wrlen_t;
+
+        // On unix when a socket is shut down all further reads return 0, so we
+        // do the same on windows to map a shut down socket to returning EOF.
+        unsafe {
+            match c::recvfrom(self.0,
+                              buf.as_mut_ptr() as *mut c_void,
+                              len,
+                              flags,
+                              &mut storage as *mut _ as *mut _,
+                              &mut addrlen) {
+                -1 if c::WSAGetLastError() == c::WSAESHUTDOWN => {
+                    Ok((0, net::sockaddr_to_addr(&storage, addrlen as usize)?))
+                },
+                -1 => Err(last_error()),
+                n => Ok((n as usize, net::sockaddr_to_addr(&storage, addrlen as usize)?)),
+            }
+        }
+    }
+
+    pub fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.recv_from_with_flags(buf, 0)
+    }
+
+    pub fn peek_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.recv_from_with_flags(buf, c::MSG_PEEK)
+    }
+
     pub fn read_to_end(&self, buf: &mut Vec<u8>) -> io::Result<usize> {
         let mut me = self;
         (&mut me).read_to_end(buf)
diff --git a/src/libstd/sys_common/net.rs b/src/libstd/sys_common/net.rs
index 10ad61f4c80..3cdeb511945 100644
--- a/src/libstd/sys_common/net.rs
+++ b/src/libstd/sys_common/net.rs
@@ -91,7 +91,7 @@ fn sockname<F>(f: F) -> io::Result<SocketAddr>
     }
 }
 
-fn sockaddr_to_addr(storage: &c::sockaddr_storage,
+pub fn sockaddr_to_addr(storage: &c::sockaddr_storage,
                     len: usize) -> io::Result<SocketAddr> {
     match storage.ss_family as c_int {
         c::AF_INET => {
@@ -222,6 +222,10 @@ impl TcpStream {
         self.inner.timeout(c::SO_SNDTIMEO)
     }
 
+    pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.inner.peek(buf)
+    }
+
     pub fn read(&self, buf: &mut [u8]) -> io::Result<usize> {
         self.inner.read(buf)
     }
@@ -441,17 +445,11 @@ impl UdpSocket {
     }
 
     pub fn recv_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
-        let mut storage: c::sockaddr_storage = unsafe { mem::zeroed() };
-        let mut addrlen = mem::size_of_val(&storage) as c::socklen_t;
-        let len = cmp::min(buf.len(), <wrlen_t>::max_value() as usize) as wrlen_t;
+        self.inner.recv_from(buf)
+    }
 
-        let n = cvt(unsafe {
-            c::recvfrom(*self.inner.as_inner(),
-                        buf.as_mut_ptr() as *mut c_void,
-                        len, 0,
-                        &mut storage as *mut _ as *mut _, &mut addrlen)
-        })?;
-        Ok((n as usize, sockaddr_to_addr(&storage, addrlen as usize)?))
+    pub fn peek_from(&self, buf: &mut [u8]) -> io::Result<(usize, SocketAddr)> {
+        self.inner.peek_from(buf)
     }
 
     pub fn send_to(&self, buf: &[u8], dst: &SocketAddr) -> io::Result<usize> {
@@ -578,6 +576,10 @@ impl UdpSocket {
         self.inner.read(buf)
     }
 
+    pub fn peek(&self, buf: &mut [u8]) -> io::Result<usize> {
+        self.inner.peek(buf)
+    }
+
     pub fn send(&self, buf: &[u8]) -> io::Result<usize> {
         let len = cmp::min(buf.len(), <wrlen_t>::max_value() as usize) as wrlen_t;
         let ret = cvt(unsafe {
diff --git a/src/libstd/thread/local.rs b/src/libstd/thread/local.rs
index 01584979aab..5166ddf8a21 100644
--- a/src/libstd/thread/local.rs
+++ b/src/libstd/thread/local.rs
@@ -99,7 +99,7 @@ pub struct LocalKey<T: 'static> {
     init: fn() -> T,
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<T: 'static> fmt::Debug for LocalKey<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("LocalKey { .. }")
@@ -332,7 +332,6 @@ pub mod os {
         marker: marker::PhantomData<Cell<T>>,
     }
 
-    #[stable(feature = "std_debug", since = "1.15.0")]
     impl<T> fmt::Debug for Key<T> {
         fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
             f.pad("Key { .. }")
diff --git a/src/libstd/thread/mod.rs b/src/libstd/thread/mod.rs
index 8789006436c..93e320c4522 100644
--- a/src/libstd/thread/mod.rs
+++ b/src/libstd/thread/mod.rs
@@ -698,7 +698,7 @@ impl ThreadId {
     }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[unstable(feature = "thread_id", issue = "21507")]
 impl fmt::Debug for ThreadId {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("ThreadId { .. }")
@@ -1002,7 +1002,7 @@ impl<T> IntoInner<imp::Thread> for JoinHandle<T> {
     fn into_inner(self) -> imp::Thread { self.0.native.unwrap() }
 }
 
-#[stable(feature = "std_debug", since = "1.15.0")]
+#[stable(feature = "std_debug", since = "1.16.0")]
 impl<T> fmt::Debug for JoinHandle<T> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         f.pad("JoinHandle { .. }")