Auto merge of #5509 - Eh2406:use_the_new, r=alexcrichton

Use the new stable

The new rust release has stabilized `Box::leak` and `impl Iterator` lets use them!

src/cargo/core/interning.rs

@@ -3,23 +3,14 @@ use serde::{Serialize, Serializer};
 use std::fmt;
 use std::sync::RwLock;
 use std::collections::HashSet;
-use std::slice;
 use std::str;
-use std::mem;
 use std::ptr;
 use std::cmp::Ordering;
 use std::ops::Deref;
 use std::hash::{Hash, Hasher};
 
 pub fn leak(s: String) -> &'static str {
-    let boxed = s.into_boxed_str();
-    let ptr = boxed.as_ptr();
-    let len = boxed.len();
-    mem::forget(boxed);
-    unsafe {
-        let slice = slice::from_raw_parts(ptr, len);
-        str::from_utf8_unchecked(slice)
-    }
+    Box::leak(s.into_boxed_str())
 }
 
 lazy_static! {

src/cargo/core/resolver/types.rs

@@ -206,13 +206,10 @@ impl DepsFrame {
             .unwrap_or(0)
     }
 
-    pub fn flatten<'s>(&'s self) -> Box<Iterator<Item = (&PackageId, Dependency)> + 's> {
-        // TODO: with impl Trait the Box can be removed
-        Box::new(
-            self.remaining_siblings
-                .clone()
-                .map(move |(_, (d, _, _))| (self.parent.package_id(), d)),
-        )
+    pub fn flatten<'s>(&'s self) -> impl Iterator<Item=(&PackageId, Dependency)> + 's {
+        self.remaining_siblings
+            .clone()
+            .map(move |(_, (d, _, _))| (self.parent.package_id(), d))
     }
 }