Auto merge of #44634 - alexcrichton:rollup, r=alexcrichton

Rollup of 19 pull requests

- Successful merges: #44273, #44356, #44395, #44531, #44537, #44542, #44560, #44567, #44574, #44577, #44586, #44589, #44590, #44593, #44598, #44606, #44609, #44616, #44631
- Failed merges:

3 files changed, 95 insertions, 1 deletions

diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs
index fbb69ca9749..96af2272578 100644
--- a/src/libstd/collections/hash/map.rs
+++ b/src/libstd/collections/hash/map.rs
@@ -588,6 +588,9 @@ impl<K, V, S> HashMap<K, V, S>
 impl<K: Hash + Eq, V> HashMap<K, V, RandomState> {
     /// Creates an empty `HashMap`.
     ///
+    /// The hash map is initially created with a capacity of 0, so it will not allocate until it
+    /// is first inserted into.
+    ///
     /// # Examples
     ///
     /// ```
diff --git a/src/libstd/collections/hash/set.rs b/src/libstd/collections/hash/set.rs
index 9771363d545..51698ce7c17 100644
--- a/src/libstd/collections/hash/set.rs
+++ b/src/libstd/collections/hash/set.rs
@@ -125,6 +125,9 @@ pub struct HashSet<T, S = RandomState> {
 impl<T: Hash + Eq> HashSet<T, RandomState> {
     /// Creates an empty `HashSet`.
     ///
+    /// The hash set is initially created with a capacity of 0, so it will not allocate until it
+    /// is first inserted into.
+    ///
     /// # Examples
     ///
     /// ```
diff --git a/src/libstd/net/ip.rs b/src/libstd/net/ip.rs
index 0abf8179cc9..eea604943af 100644
--- a/src/libstd/net/ip.rs
+++ b/src/libstd/net/ip.rs
@@ -10,7 +10,7 @@
 
 #![unstable(feature = "ip", reason = "extra functionality has not been \
                                       scrutinized to the level that it should \
-                                      be stable",
+                                      be to be stable",
             issue = "27709")]
 
 use cmp::Ordering;
@@ -342,6 +342,42 @@ impl Ipv4Addr {
         }
     }
 
+    /// Creates a new IPv4 address with the address pointing to localhost: 127.0.0.1.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip_constructors)]
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let addr = Ipv4Addr::localhost();
+    /// assert_eq!(addr, Ipv4Addr::new(127, 0, 0, 1));
+    /// ```
+    #[unstable(feature = "ip_constructors",
+               reason = "requires greater scrutiny before stabilization",
+               issue = "44582")]
+    pub fn localhost() -> Ipv4Addr {
+        Ipv4Addr::new(127, 0, 0, 1)
+    }
+
+    /// Creates a new IPv4 address representing an unspecified address: 0.0.0.0
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip_constructors)]
+    /// use std::net::Ipv4Addr;
+    ///
+    /// let addr = Ipv4Addr::unspecified();
+    /// assert_eq!(addr, Ipv4Addr::new(0, 0, 0, 0));
+    /// ```
+    #[unstable(feature = "ip_constructors",
+               reason = "requires greater scrutiny before stabilization",
+               issue = "44582")]
+    pub fn unspecified() -> Ipv4Addr {
+        Ipv4Addr::new(0, 0, 0, 0)
+    }
+
     /// Returns the four eight-bit integers that make up this address.
     ///
     /// # Examples
@@ -788,6 +824,42 @@ impl Ipv6Addr {
         Ipv6Addr { inner: addr }
     }
 
+    /// Creates a new IPv6 address representing localhost: `::1`.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip_constructors)]
+    /// use std::net::Ipv6Addr;
+    ///
+    /// let addr = Ipv6Addr::localhost();
+    /// assert_eq!(addr, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
+    /// ```
+    #[unstable(feature = "ip_constructors",
+               reason = "requires greater scrutiny before stabilization",
+               issue = "44582")]
+    pub fn localhost() -> Ipv6Addr {
+        Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1)
+    }
+
+    /// Creates a new IPv6 address representing the unspecified address: `::`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(ip_constructors)]
+    /// use std::net::Ipv6Addr;
+    ///
+    /// let addr = Ipv6Addr::unspecified();
+    /// assert_eq!(addr, Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0));
+    /// ```
+    #[unstable(feature = "ip_constructors",
+               reason = "requires greater scrutiny before stabilization",
+               issue = "44582")]
+    pub fn unspecified() -> Ipv6Addr {
+        Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0)
+    }
+
     /// Returns the eight 16-bit segments that make up this address.
     ///
     /// # Examples
@@ -1682,6 +1754,22 @@ mod tests {
     }
 
     #[test]
+    fn ipv4_from_constructors() {
+        assert_eq!(Ipv4Addr::localhost(), Ipv4Addr::new(127, 0, 0, 1));
+        assert!(Ipv4Addr::localhost().is_loopback());
+        assert_eq!(Ipv4Addr::unspecified(), Ipv4Addr::new(0, 0, 0, 0));
+        assert!(Ipv4Addr::unspecified().is_unspecified());
+    }
+
+    #[test]
+    fn ipv6_from_contructors() {
+        assert_eq!(Ipv6Addr::localhost(), Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 1));
+        assert!(Ipv6Addr::localhost().is_loopback());
+        assert_eq!(Ipv6Addr::unspecified(), Ipv6Addr::new(0, 0, 0, 0, 0, 0, 0, 0));
+        assert!(Ipv6Addr::unspecified().is_unspecified());
+    }
+
+    #[test]
     fn ipv4_from_octets() {
         assert_eq!(Ipv4Addr::from([127, 0, 0, 1]), Ipv4Addr::new(127, 0, 0, 1))
     }