Merge remote-tracking branch 'upstream/master'

28 files changed, 954 insertions, 152 deletions

diff --git a/src/libcore/benches/iter.rs b/src/libcore/benches/iter.rs
index 827c6354c60..1f16f5b1df3 100644
--- a/src/libcore/benches/iter.rs
+++ b/src/libcore/benches/iter.rs
@@ -147,40 +147,131 @@ fn bench_for_each_chain_ref_fold(b: &mut Bencher) {
     });
 }
 
-#[bench]
-fn bench_flat_map_sum(b: &mut Bencher) {
-    b.iter(|| -> i64 {
-        (0i64..1000).flat_map(|x| x..x+1000)
-            .map(black_box)
-            .sum()
-    });
+
+/// Helper to benchmark `sum` for iterators taken by value which
+/// can optimize `fold`, and by reference which cannot.
+macro_rules! bench_sums {
+    ($bench_sum:ident, $bench_ref_sum:ident, $iter:expr) => {
+        #[bench]
+        fn $bench_sum(b: &mut Bencher) {
+            b.iter(|| -> i64 {
+                $iter.map(black_box).sum()
+            });
+        }
+
+        #[bench]
+        fn $bench_ref_sum(b: &mut Bencher) {
+            b.iter(|| -> i64 {
+                $iter.map(black_box).by_ref().sum()
+            });
+        }
+    }
 }
 
-#[bench]
-fn bench_flat_map_ref_sum(b: &mut Bencher) {
-    b.iter(|| -> i64 {
-        (0i64..1000).flat_map(|x| x..x+1000)
-            .map(black_box)
-            .by_ref()
-            .sum()
-    });
+bench_sums! {
+    bench_flat_map_sum,
+    bench_flat_map_ref_sum,
+    (0i64..1000).flat_map(|x| x..x+1000)
 }
 
-#[bench]
-fn bench_flat_map_chain_sum(b: &mut Bencher) {
-    b.iter(|| -> i64 {
-        (0i64..1000000).flat_map(|x| once(x).chain(once(x)))
-            .map(black_box)
-            .sum()
-    });
+bench_sums! {
+    bench_flat_map_chain_sum,
+    bench_flat_map_chain_ref_sum,
+    (0i64..1000000).flat_map(|x| once(x).chain(once(x)))
 }
 
-#[bench]
-fn bench_flat_map_chain_ref_sum(b: &mut Bencher) {
-    b.iter(|| -> i64 {
-        (0i64..1000000).flat_map(|x| once(x).chain(once(x)))
-            .map(black_box)
-            .by_ref()
-            .sum()
-    });
+bench_sums! {
+    bench_enumerate_sum,
+    bench_enumerate_ref_sum,
+    (0i64..1000000).enumerate().map(|(i, x)| x * i as i64)
+}
+
+bench_sums! {
+    bench_enumerate_chain_sum,
+    bench_enumerate_chain_ref_sum,
+    (0i64..1000000).chain(0..1000000).enumerate().map(|(i, x)| x * i as i64)
+}
+
+bench_sums! {
+    bench_filter_sum,
+    bench_filter_ref_sum,
+    (0i64..1000000).filter(|x| x % 2 == 0)
+}
+
+bench_sums! {
+    bench_filter_chain_sum,
+    bench_filter_chain_ref_sum,
+    (0i64..1000000).chain(0..1000000).filter(|x| x % 2 == 0)
+}
+
+bench_sums! {
+    bench_filter_map_sum,
+    bench_filter_map_ref_sum,
+    (0i64..1000000).filter_map(|x| x.checked_mul(x))
+}
+
+bench_sums! {
+    bench_filter_map_chain_sum,
+    bench_filter_map_chain_ref_sum,
+    (0i64..1000000).chain(0..1000000).filter_map(|x| x.checked_mul(x))
+}
+
+bench_sums! {
+    bench_fuse_sum,
+    bench_fuse_ref_sum,
+    (0i64..1000000).fuse()
+}
+
+bench_sums! {
+    bench_fuse_chain_sum,
+    bench_fuse_chain_ref_sum,
+    (0i64..1000000).chain(0..1000000).fuse()
+}
+
+bench_sums! {
+    bench_inspect_sum,
+    bench_inspect_ref_sum,
+    (0i64..1000000).inspect(|_| {})
+}
+
+bench_sums! {
+    bench_inspect_chain_sum,
+    bench_inspect_chain_ref_sum,
+    (0i64..1000000).chain(0..1000000).inspect(|_| {})
+}
+
+bench_sums! {
+    bench_peekable_sum,
+    bench_peekable_ref_sum,
+    (0i64..1000000).peekable()
+}
+
+bench_sums! {
+    bench_peekable_chain_sum,
+    bench_peekable_chain_ref_sum,
+    (0i64..1000000).chain(0..1000000).peekable()
+}
+
+bench_sums! {
+    bench_skip_sum,
+    bench_skip_ref_sum,
+    (0i64..1000000).skip(1000)
+}
+
+bench_sums! {
+    bench_skip_chain_sum,
+    bench_skip_chain_ref_sum,
+    (0i64..1000000).chain(0..1000000).skip(1000)
+}
+
+bench_sums! {
+    bench_skip_while_sum,
+    bench_skip_while_ref_sum,
+    (0i64..1000000).skip_while(|&x| x < 1000)
+}
+
+bench_sums! {
+    bench_skip_while_chain_sum,
+    bench_skip_while_chain_ref_sum,
+    (0i64..1000000).chain(0..1000000).skip_while(|&x| x < 1000)
 }
diff --git a/src/libcore/cmp.rs b/src/libcore/cmp.rs
index 6f86f8caad0..e012cbd76ff 100644
--- a/src/libcore/cmp.rs
+++ b/src/libcore/cmp.rs
@@ -456,7 +456,7 @@ pub trait Ord: Eq + PartialOrd<Self> {
     /// assert_eq!(2, 1.max(2));
     /// assert_eq!(2, 2.max(2));
     /// ```
-    #[stable(feature = "ord_max_min", since = "1.22.0")]
+    #[stable(feature = "ord_max_min", since = "1.21.0")]
     fn max(self, other: Self) -> Self
     where Self: Sized {
         if other >= self { other } else { self }
@@ -472,7 +472,7 @@ pub trait Ord: Eq + PartialOrd<Self> {
     /// assert_eq!(1, 1.min(2));
     /// assert_eq!(2, 2.min(2));
     /// ```
-    #[stable(feature = "ord_max_min", since = "1.22.0")]
+    #[stable(feature = "ord_max_min", since = "1.21.0")]
     fn min(self, other: Self) -> Self
     where Self: Sized {
         if self <= other { self } else { other }
diff --git a/src/libcore/convert.rs b/src/libcore/convert.rs
index 6f3c3863fae..e815d72d366 100644
--- a/src/libcore/convert.rs
+++ b/src/libcore/convert.rs
@@ -48,8 +48,25 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use str::FromStr;
+use fmt;
 
+/// A type used as the error type for implementations of fallible conversion
+/// traits in cases where conversions cannot actually fail.
+///
+/// Because `Infallible` has no variants, a value of this type can never exist.
+/// It is used only to satisfy trait signatures that expect an error type, and
+/// signals to both the compiler and the user that the error case is impossible.
+#[unstable(feature = "try_from", issue = "33417")]
+#[derive(Clone, Copy, Debug, Eq, Hash, Ord, PartialEq, PartialOrd)]
+pub enum Infallible {}
+
+#[unstable(feature = "try_from", issue = "33417")]
+impl fmt::Display for Infallible {
+    fn fmt(&self, _: &mut fmt::Formatter) -> fmt::Result {
+        match *self {
+        }
+    }
+}
 /// A cheap reference-to-reference conversion. Used to convert a value to a
 /// reference value within generic code.
 ///
@@ -417,6 +434,17 @@ impl<T, U> TryInto<U> for T where U: TryFrom<T>
     }
 }
 
+// Infallible conversions are semantically equivalent to fallible conversions
+// with an uninhabited error type.
+#[unstable(feature = "try_from", issue = "33417")]
+impl<T, U> TryFrom<U> for T where T: From<U> {
+    type Error = Infallible;
+
+    fn try_from(value: U) -> Result<Self, Self::Error> {
+        Ok(T::from(value))
+    }
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // CONCRETE IMPLS
 ////////////////////////////////////////////////////////////////////////////////
@@ -442,14 +470,3 @@ impl AsRef<str> for str {
         self
     }
 }
-
-// FromStr implies TryFrom<&str>
-#[unstable(feature = "try_from", issue = "33417")]
-impl<'a, T> TryFrom<&'a str> for T where T: FromStr
-{
-    type Error = <T as FromStr>::Err;
-
-    fn try_from(s: &'a str) -> Result<T, Self::Error> {
-        FromStr::from_str(s)
-    }
-}
diff --git a/src/libcore/fmt/mod.rs b/src/libcore/fmt/mod.rs
index cf6262bda97..6c251b9eb09 100644
--- a/src/libcore/fmt/mod.rs
+++ b/src/libcore/fmt/mod.rs
@@ -488,13 +488,14 @@ impl<'a> Display for Arguments<'a> {
 /// The origin is: Point { x: 0, y: 0 }
 /// ```
 ///
-/// There are a number of `debug_*` methods on `Formatter` to help you with manual
+/// There are a number of `debug_*` methods on [`Formatter`] to help you with manual
 /// implementations, such as [`debug_struct`][debug_struct].
 ///
 /// `Debug` implementations using either `derive` or the debug builder API
-/// on `Formatter` support pretty printing using the alternate flag: `{:#?}`.
+/// on [`Formatter`] support pretty printing using the alternate flag: `{:#?}`.
 ///
 /// [debug_struct]: ../../std/fmt/struct.Formatter.html#method.debug_struct
+/// [`Formatter`]: ../../std/fmt/struct.Formatter.html
 ///
 /// Pretty printing with `#?`:
 ///
@@ -1321,8 +1322,11 @@ impl<'a> Formatter<'a> {
         self.flags & (1 << FlagV1::SignAwareZeroPad as u32) != 0
     }
 
-    /// Creates a `DebugStruct` builder designed to assist with creation of
-    /// `fmt::Debug` implementations for structs.
+    /// Creates a [`DebugStruct`] builder designed to assist with creation of
+    /// [`fmt::Debug`] implementations for structs.
+    ///
+    /// [`DebugStruct`]: ../../std/fmt/struct.DebugStruct.html
+    /// [`fmt::Debug`]: ../../std/fmt/trait.Debug.html
     ///
     /// # Examples
     ///
@@ -1700,8 +1704,18 @@ impl<T: ?Sized + Debug> Debug for RefCell<T> {
                     .finish()
             }
             Err(_) => {
+                // The RefCell is mutably borrowed so we can't look at its value
+                // here. Show a placeholder instead.
+                struct BorrowedPlaceholder;
+
+                impl Debug for BorrowedPlaceholder {
+                    fn fmt(&self, f: &mut Formatter) -> Result {
+                        f.write_str("<borrowed>")
+                    }
+                }
+
                 f.debug_struct("RefCell")
-                    .field("value", &"<borrowed>")
+                    .field("value", &BorrowedPlaceholder)
                     .finish()
             }
         }
diff --git a/src/libcore/internal_macros.rs b/src/libcore/internal_macros.rs
index 9a7914064fd..cb215a38e53 100644
--- a/src/libcore/internal_macros.rs
+++ b/src/libcore/internal_macros.rs
@@ -68,3 +68,22 @@ macro_rules! forward_ref_binop {
         }
     }
 }
+
+// implements "T op= &U", based on "T op= U"
+// where U is expected to be `Copy`able
+macro_rules! forward_ref_op_assign {
+    (impl $imp:ident, $method:ident for $t:ty, $u:ty) => {
+        forward_ref_op_assign!(impl $imp, $method for $t, $u,
+                #[stable(feature = "op_assign_builtins_by_ref", since = "1.22.0")]);
+    };
+    (impl $imp:ident, $method:ident for $t:ty, $u:ty, #[$attr:meta]) => {
+        #[$attr]
+        impl<'a> $imp<&'a $u> for $t {
+            #[inline]
+            fn $method(&mut self, other: &'a $u) {
+                $imp::$method(self, *other);
+            }
+        }
+    }
+}
+
diff --git a/src/libcore/iter/iterator.rs b/src/libcore/iter/iterator.rs
index edafd0ce2c2..e9e31065cf8 100644
--- a/src/libcore/iter/iterator.rs
+++ b/src/libcore/iter/iterator.rs
@@ -518,7 +518,7 @@ pub trait Iterator {
     ///       .for_each(|(i, x)| println!("{}:{}", i, x));
     /// ```
     #[inline]
-    #[stable(feature = "iterator_for_each", since = "1.22.0")]
+    #[stable(feature = "iterator_for_each", since = "1.21.0")]
     fn for_each<F>(self, mut f: F) where
         Self: Sized, F: FnMut(Self::Item),
     {
@@ -1337,7 +1337,7 @@ pub trait Iterator {
         (left, right)
     }
 
-    /// An iterator adaptor that applies a function, producing a single, final value.
+    /// An iterator method that applies a function, producing a single, final value.
     ///
     /// `fold()` takes two arguments: an initial value, and a closure with two
     /// arguments: an 'accumulator', and an element. The closure returns the value that
diff --git a/src/libcore/iter/mod.rs b/src/libcore/iter/mod.rs
index a596ffd6ae8..8d2521b053e 100644
--- a/src/libcore/iter/mod.rs
+++ b/src/libcore/iter/mod.rs
@@ -359,6 +359,12 @@ impl<I> Iterator for Rev<I> where I: DoubleEndedIterator {
     #[inline]
     fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
 
+    fn fold<Acc, F>(self, init: Acc, f: F) -> Acc
+        where F: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.iter.rfold(init, f)
+    }
+
     #[inline]
     fn find<P>(&mut self, predicate: P) -> Option<Self::Item>
         where P: FnMut(&Self::Item) -> bool
@@ -379,6 +385,12 @@ impl<I> DoubleEndedIterator for Rev<I> where I: DoubleEndedIterator {
     #[inline]
     fn next_back(&mut self) -> Option<<I as Iterator>::Item> { self.iter.next() }
 
+    fn rfold<Acc, F>(self, init: Acc, f: F) -> Acc
+        where F: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.iter.fold(init, f)
+    }
+
     fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item>
         where P: FnMut(&Self::Item) -> bool
     {
@@ -449,6 +461,12 @@ impl<'a, I, T: 'a> DoubleEndedIterator for Cloned<I>
     fn next_back(&mut self) -> Option<T> {
         self.it.next_back().cloned()
     }
+
+    fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
+        where F: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.it.rfold(init, move |acc, elt| f(acc, elt.clone()))
+    }
 }
 
 #[stable(feature = "iter_cloned", since = "1.1.0")]
@@ -470,7 +488,7 @@ impl<'a, I, T: 'a> FusedIterator for Cloned<I>
 {}
 
 #[doc(hidden)]
-unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
+default unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
     where I: TrustedRandomAccess<Item=&'a T>, T: Clone
 {
     unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
@@ -481,6 +499,18 @@ unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
     fn may_have_side_effect() -> bool { true }
 }
 
+#[doc(hidden)]
+unsafe impl<'a, I, T: 'a> TrustedRandomAccess for Cloned<I>
+    where I: TrustedRandomAccess<Item=&'a T>, T: Copy
+{
+    unsafe fn get_unchecked(&mut self, i: usize) -> Self::Item {
+        *self.it.get_unchecked(i)
+    }
+
+    #[inline]
+    fn may_have_side_effect() -> bool { false }
+}
+
 #[unstable(feature = "trusted_len", issue = "37572")]
 unsafe impl<'a, I, T: 'a> TrustedLen for Cloned<I>
     where I: TrustedLen<Item=&'a T>,
@@ -528,7 +558,7 @@ impl<I> Iterator for Cycle<I> where I: Clone + Iterator {
 #[unstable(feature = "fused", issue = "35602")]
 impl<I> FusedIterator for Cycle<I> where I: Clone + Iterator {}
 
-/// An adapter for stepping iterators by a custom amount.
+/// An iterator for stepping iterators by a custom amount.
 ///
 /// This `struct` is created by the [`step_by`] method on [`Iterator`]. See
 /// its documentation for more.
@@ -761,6 +791,26 @@ impl<A, B> DoubleEndedIterator for Chain<A, B> where
             ChainState::Back => self.b.next_back(),
         }
     }
+
+    fn rfold<Acc, F>(self, init: Acc, mut f: F) -> Acc
+        where F: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut accum = init;
+        match self.state {
+            ChainState::Both | ChainState::Back => {
+                accum = self.b.rfold(accum, &mut f);
+            }
+            _ => { }
+        }
+        match self.state {
+            ChainState::Both | ChainState::Front => {
+                accum = self.a.rfold(accum, &mut f);
+            }
+            _ => { }
+        }
+        accum
+    }
+
 }
 
 // Note: *both* must be fused to handle double-ended iterators.
@@ -1094,6 +1144,13 @@ impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for Map<I, F> where
     fn next_back(&mut self) -> Option<B> {
         self.iter.next_back().map(&mut self.f)
     }
+
+    fn rfold<Acc, G>(self, init: Acc, mut g: G) -> Acc
+        where G: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut f = self.f;
+        self.iter.rfold(init, move |acc, elt| g(acc, f(elt)))
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1193,6 +1250,18 @@ impl<I: Iterator, P> Iterator for Filter<I, P> where P: FnMut(&I::Item) -> bool
         }
         count
     }
+
+    #[inline]
+    fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut predicate = self.predicate;
+        self.iter.fold(init, move |acc, item| if predicate(&item) {
+            fold(acc, item)
+        } else {
+            acc
+        })
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1208,6 +1277,18 @@ impl<I: DoubleEndedIterator, P> DoubleEndedIterator for Filter<I, P>
         }
         None
     }
+
+    #[inline]
+    fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut predicate = self.predicate;
+        self.iter.rfold(init, move |acc, item| if predicate(&item) {
+            fold(acc, item)
+        } else {
+            acc
+        })
+    }
 }
 
 #[unstable(feature = "fused", issue = "35602")]
@@ -1259,6 +1340,17 @@ impl<B, I: Iterator, F> Iterator for FilterMap<I, F>
         let (_, upper) = self.iter.size_hint();
         (0, upper) // can't know a lower bound, due to the predicate
     }
+
+    #[inline]
+    fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut f = self.f;
+        self.iter.fold(init, move |acc, item| match f(item) {
+            Some(x) => fold(acc, x),
+            None => acc,
+        })
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1274,6 +1366,17 @@ impl<B, I: DoubleEndedIterator, F> DoubleEndedIterator for FilterMap<I, F>
         }
         None
     }
+
+    #[inline]
+    fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut f = self.f;
+        self.iter.rfold(init, move |acc, item| match f(item) {
+            Some(x) => fold(acc, x),
+            None => acc,
+        })
+    }
 }
 
 #[unstable(feature = "fused", issue = "35602")]
@@ -1338,6 +1441,19 @@ impl<I> Iterator for Enumerate<I> where I: Iterator {
     fn count(self) -> usize {
         self.iter.count()
     }
+
+    #[inline]
+    #[rustc_inherit_overflow_checks]
+    fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut count = self.count;
+        self.iter.fold(init, move |acc, item| {
+            let acc = fold(acc, (count, item));
+            count += 1;
+            acc
+        })
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1353,6 +1469,19 @@ impl<I> DoubleEndedIterator for Enumerate<I> where
             (self.count + len, a)
         })
     }
+
+    #[inline]
+    fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        // Can safely add and subtract the count, as `ExactSizeIterator` promises
+        // that the number of elements fits into a `usize`.
+        let mut count = self.count + self.iter.len();
+        self.iter.rfold(init, move |acc, item| {
+            count -= 1;
+            fold(acc, (count, item))
+        })
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1464,6 +1593,18 @@ impl<I: Iterator> Iterator for Peekable<I> {
         let hi = hi.and_then(|x| x.checked_add(peek_len));
         (lo, hi)
     }
+
+    #[inline]
+    fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let acc = match self.peeked {
+            Some(None) => return init,
+            Some(Some(v)) => fold(init, v),
+            None => init,
+        };
+        self.iter.fold(acc, fold)
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1572,6 +1713,19 @@ impl<I: Iterator, P> Iterator for SkipWhile<I, P>
         let (_, upper) = self.iter.size_hint();
         (0, upper) // can't know a lower bound, due to the predicate
     }
+
+    #[inline]
+    fn fold<Acc, Fold>(mut self, mut init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        if !self.flag {
+            match self.next() {
+                Some(v) => init = fold(init, v),
+                None => return init,
+            }
+        }
+        self.iter.fold(init, fold)
+    }
 }
 
 #[unstable(feature = "fused", issue = "35602")]
@@ -1712,6 +1866,19 @@ impl<I> Iterator for Skip<I> where I: Iterator {
 
         (lower, upper)
     }
+
+    #[inline]
+    fn fold<Acc, Fold>(mut self, init: Acc, fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        if self.n > 0 {
+            // nth(n) skips n+1
+            if self.iter.nth(self.n - 1).is_none() {
+                return init;
+            }
+        }
+        self.iter.fold(init, fold)
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -1934,6 +2101,16 @@ impl<I: DoubleEndedIterator, U, F> DoubleEndedIterator for FlatMap<I, U, F> wher
             }
         }
     }
+
+    #[inline]
+    fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.frontiter.into_iter()
+            .chain(self.iter.map(self.f).map(U::into_iter))
+            .chain(self.backiter)
+            .rfold(init, |acc, iter| iter.rfold(acc, &mut fold))
+    }
 }
 
 #[unstable(feature = "fused", issue = "35602")]
@@ -2011,6 +2188,17 @@ impl<I> Iterator for Fuse<I> where I: Iterator {
             self.iter.size_hint()
         }
     }
+
+    #[inline]
+    default fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        if self.done {
+            init
+        } else {
+            self.iter.fold(init, fold)
+        }
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -2025,6 +2213,17 @@ impl<I> DoubleEndedIterator for Fuse<I> where I: DoubleEndedIterator {
             next
         }
     }
+
+    #[inline]
+    default fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        if self.done {
+            init
+        } else {
+            self.iter.rfold(init, fold)
+        }
+    }
 }
 
 unsafe impl<I> TrustedRandomAccess for Fuse<I>
@@ -2065,6 +2264,13 @@ impl<I> Iterator for Fuse<I> where I: FusedIterator {
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.iter.size_hint()
     }
+
+    #[inline]
+    fn fold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.iter.fold(init, fold)
+    }
 }
 
 #[unstable(feature = "fused", reason = "recently added", issue = "35602")]
@@ -2075,6 +2281,13 @@ impl<I> DoubleEndedIterator for Fuse<I>
     fn next_back(&mut self) -> Option<<I as Iterator>::Item> {
         self.iter.next_back()
     }
+
+    #[inline]
+    fn rfold<Acc, Fold>(self, init: Acc, fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        self.iter.rfold(init, fold)
+    }
 }
 
 
@@ -2139,6 +2352,14 @@ impl<I: Iterator, F> Iterator for Inspect<I, F> where F: FnMut(&I::Item) {
     fn size_hint(&self) -> (usize, Option<usize>) {
         self.iter.size_hint()
     }
+
+    #[inline]
+    fn fold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut f = self.f;
+        self.iter.fold(init, move |acc, item| { f(&item); fold(acc, item) })
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -2150,6 +2371,14 @@ impl<I: DoubleEndedIterator, F> DoubleEndedIterator for Inspect<I, F>
         let next = self.iter.next_back();
         self.do_inspect(next)
     }
+
+    #[inline]
+    fn rfold<Acc, Fold>(self, init: Acc, mut fold: Fold) -> Acc
+        where Fold: FnMut(Acc, Self::Item) -> Acc,
+    {
+        let mut f = self.f;
+        self.iter.rfold(init, move |acc, item| { f(&item); fold(acc, item) })
+    }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libcore/iter/range.rs b/src/libcore/iter/range.rs
index 73d518b570a..e9aee4a4676 100644
--- a/src/libcore/iter/range.rs
+++ b/src/libcore/iter/range.rs
@@ -89,6 +89,7 @@ macro_rules! step_impl_unsigned {
             }
 
             #[inline]
+            #[allow(unreachable_patterns)]
             fn add_usize(&self, n: usize) -> Option<Self> {
                 match <$t>::try_from(n) {
                     Ok(n_as_t) => self.checked_add(n_as_t),
@@ -120,6 +121,7 @@ macro_rules! step_impl_signed {
             }
 
             #[inline]
+            #[allow(unreachable_patterns)]
             fn add_usize(&self, n: usize) -> Option<Self> {
                 match <$unsigned>::try_from(n) {
                     Ok(n_as_unsigned) => {
diff --git a/src/libcore/iter/traits.rs b/src/libcore/iter/traits.rs
index 7ef50396c82..28236d193c3 100644
--- a/src/libcore/iter/traits.rs
+++ b/src/libcore/iter/traits.rs
@@ -415,6 +415,70 @@ pub trait DoubleEndedIterator: Iterator {
     #[stable(feature = "rust1", since = "1.0.0")]
     fn next_back(&mut self) -> Option<Self::Item>;
 
+    /// An iterator method that reduces the iterator's elements to a single,
+    /// final value, starting from the back.
+    ///
+    /// This is the reverse version of [`fold()`]: it takes elements starting from
+    /// the back of the iterator.
+    ///
+    /// `rfold()` takes two arguments: an initial value, and a closure with two
+    /// arguments: an 'accumulator', and an element. The closure returns the value that
+    /// the accumulator should have for the next iteration.
+    ///
+    /// The initial value is the value the accumulator will have on the first
+    /// call.
+    ///
+    /// After applying this closure to every element of the iterator, `rfold()`
+    /// returns the accumulator.
+    ///
+    /// This operation is sometimes called 'reduce' or 'inject'.
+    ///
+    /// Folding is useful whenever you have a collection of something, and want
+    /// to produce a single value from it.
+    ///
+    /// [`fold()`]: trait.Iterator.html#method.fold
+    ///
+    /// # Examples
+    ///
+    /// Basic usage:
+    ///
+    /// ```
+    /// #![feature(iter_rfold)]
+    /// let a = [1, 2, 3];
+    ///
+    /// // the sum of all of the elements of a
+    /// let sum = a.iter()
+    ///            .rfold(0, |acc, &x| acc + x);
+    ///
+    /// assert_eq!(sum, 6);
+    /// ```
+    ///
+    /// This example builds a string, starting with an initial value
+    /// and continuing with each element from the back until the front:
+    ///
+    /// ```
+    /// #![feature(iter_rfold)]
+    /// let numbers = [1, 2, 3, 4, 5];
+    ///
+    /// let zero = "0".to_string();
+    ///
+    /// let result = numbers.iter().rfold(zero, |acc, &x| {
+    ///     format!("({} + {})", x, acc)
+    /// });
+    ///
+    /// assert_eq!(result, "(1 + (2 + (3 + (4 + (5 + 0)))))");
+    /// ```
+    #[inline]
+    #[unstable(feature = "iter_rfold", issue = "44705")]
+    fn rfold<B, F>(mut self, mut accum: B, mut f: F) -> B where
+        Self: Sized, F: FnMut(B, Self::Item) -> B,
+    {
+        while let Some(x) = self.next_back() {
+            accum = f(accum, x);
+        }
+        accum
+    }
+
     /// Searches for an element of an iterator from the right that satisfies a predicate.
     ///
     /// `rfind()` takes a closure that returns `true` or `false`. It applies
diff --git a/src/libcore/marker.rs b/src/libcore/marker.rs
index e8fd729b638..f56a9a40332 100644
--- a/src/libcore/marker.rs
+++ b/src/libcore/marker.rs
@@ -122,7 +122,7 @@ pub trait Sized {
 /// [RFC982]: https://github.com/rust-lang/rfcs/blob/master/text/0982-dst-coercion.md
 /// [nomicon-coerce]: ../../nomicon/coercions.html
 #[unstable(feature = "unsize", issue = "27732")]
-#[lang="unsize"]
+#[lang = "unsize"]
 pub trait Unsize<T: ?Sized> {
     // Empty.
 }
diff --git a/src/libcore/mem.rs b/src/libcore/mem.rs
index 34994dc3b70..c869054cee8 100644
--- a/src/libcore/mem.rs
+++ b/src/libcore/mem.rs
@@ -177,15 +177,59 @@ pub fn forget<T>(t: T) {
 
 /// Returns the size of a type in bytes.
 ///
-/// More specifically, this is the offset in bytes between successive
-/// items of the same type, including alignment padding.
+/// More specifically, this is the offset in bytes between successive elements
+/// in an array with that item type including alignment padding. Thus, for any
+/// type `T` and length `n`, `[T; n]` has a size of `n * size_of::<T>()`.
+///
+/// In general, the size of a type is not stable across compilations, but
+/// specific types such as primitives are.
+///
+/// The following table gives the size for primitives.
+///
+/// Type | size_of::\<Type>()
+/// ---- | ---------------
+/// () | 0
+/// u8 | 1
+/// u16 | 2
+/// u32 | 4
+/// u64 | 8
+/// i8 | 1
+/// i16 | 2
+/// i32 | 4
+/// i64 | 8
+/// f32 | 4
+/// f64 | 8
+/// char | 4
+///
+/// Furthermore, `usize` and `isize` have the same size.
+///
+/// The types `*const T`, `&T`, `Box<T>`, `Option<&T>`, and `Option<Box<T>>` all have
+/// the same size. If `T` is Sized, all of those types have the same size as `usize`.
+///
+/// The mutability of a pointer does not change its size. As such, `&T` and `&mut T`
+/// have the same size. Likewise for `*const T` and `*mut T`.
 ///
 /// # Examples
 ///
 /// ```
 /// use std::mem;
 ///
+/// // Some primitives
 /// assert_eq!(4, mem::size_of::<i32>());
+/// assert_eq!(8, mem::size_of::<f64>());
+/// assert_eq!(0, mem::size_of::<()>());
+///
+/// // Some arrays
+/// assert_eq!(8, mem::size_of::<[i32; 2]>());
+/// assert_eq!(12, mem::size_of::<[i32; 3]>());
+/// assert_eq!(0, mem::size_of::<[i32; 0]>());
+///
+///
+/// // Pointer size equality
+/// assert_eq!(mem::size_of::<&i32>(), mem::size_of::<*const i32>());
+/// assert_eq!(mem::size_of::<&i32>(), mem::size_of::<Box<i32>>());
+/// assert_eq!(mem::size_of::<&i32>(), mem::size_of::<Option<&i32>>());
+/// assert_eq!(mem::size_of::<Box<i32>>(), mem::size_of::<Option<Box<i32>>>());
 /// ```
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
@@ -358,7 +402,7 @@ pub fn align_of_val<T: ?Sized>(val: &T) -> usize {
 /// }
 /// ```
 #[inline]
-#[stable(feature = "needs_drop", since = "1.22.0")]
+#[stable(feature = "needs_drop", since = "1.21.0")]
 pub fn needs_drop<T>() -> bool {
     unsafe { intrinsics::needs_drop::<T>() }
 }
diff --git a/src/libcore/num/mod.rs b/src/libcore/num/mod.rs
index bf31deae7a6..85be8a08728 100644
--- a/src/libcore/num/mod.rs
+++ b/src/libcore/num/mod.rs
@@ -12,7 +12,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
-use convert::TryFrom;
+use convert::{Infallible, TryFrom};
 use fmt;
 use intrinsics;
 use str::FromStr;
@@ -2507,16 +2507,24 @@ impl fmt::Display for TryFromIntError {
     }
 }
 
+#[unstable(feature = "try_from", issue = "33417")]
+impl From<Infallible> for TryFromIntError {
+    fn from(infallible: Infallible) -> TryFromIntError {
+        match infallible {
+        }
+    }
+}
+
 // no possible bounds violation
 macro_rules! try_from_unbounded {
     ($source:ty, $($target:ty),*) => {$(
         #[unstable(feature = "try_from", issue = "33417")]
         impl TryFrom<$source> for $target {
-            type Error = TryFromIntError;
+            type Error = Infallible;
 
             #[inline]
-            fn try_from(u: $source) -> Result<$target, TryFromIntError> {
-                Ok(u as $target)
+            fn try_from(value: $source) -> Result<Self, Self::Error> {
+                Ok(value as $target)
             }
         }
     )*}
@@ -2588,31 +2596,17 @@ macro_rules! rev {
 }
 
 /// intra-sign conversions
-try_from_unbounded!(u8, u8, u16, u32, u64, u128);
-try_from_unbounded!(u16, u16, u32, u64, u128);
-try_from_unbounded!(u32, u32, u64, u128);
-try_from_unbounded!(u64, u64, u128);
-try_from_unbounded!(u128, u128);
 try_from_upper_bounded!(u16, u8);
 try_from_upper_bounded!(u32, u16, u8);
 try_from_upper_bounded!(u64, u32, u16, u8);
 try_from_upper_bounded!(u128, u64, u32, u16, u8);
 
-try_from_unbounded!(i8, i8, i16, i32, i64, i128);
-try_from_unbounded!(i16, i16, i32, i64, i128);
-try_from_unbounded!(i32, i32, i64, i128);
-try_from_unbounded!(i64, i64, i128);
-try_from_unbounded!(i128, i128);
 try_from_both_bounded!(i16, i8);
 try_from_both_bounded!(i32, i16, i8);
 try_from_both_bounded!(i64, i32, i16, i8);
 try_from_both_bounded!(i128, i64, i32, i16, i8);
 
 // unsigned-to-signed
-try_from_unbounded!(u8, i16, i32, i64, i128);
-try_from_unbounded!(u16, i32, i64, i128);
-try_from_unbounded!(u32, i64, i128);
-try_from_unbounded!(u64, i128);
 try_from_upper_bounded!(u8, i8);
 try_from_upper_bounded!(u16, i8, i16);
 try_from_upper_bounded!(u32, i8, i16, i32);
@@ -2631,15 +2625,13 @@ try_from_both_bounded!(i64, u32, u16, u8);
 try_from_both_bounded!(i128, u64, u32, u16, u8);
 
 // usize/isize
-try_from_unbounded!(usize, usize);
 try_from_upper_bounded!(usize, isize);
 try_from_lower_bounded!(isize, usize);
-try_from_unbounded!(isize, isize);
 
 #[cfg(target_pointer_width = "16")]
 mod ptr_try_from_impls {
     use super::TryFromIntError;
-    use convert::TryFrom;
+    use convert::{Infallible, TryFrom};
 
     try_from_upper_bounded!(usize, u8);
     try_from_unbounded!(usize, u16, u32, u64, u128);
@@ -2651,21 +2643,21 @@ mod ptr_try_from_impls {
     try_from_both_bounded!(isize, i8);
     try_from_unbounded!(isize, i16, i32, i64, i128);
 
-    rev!(try_from_unbounded, usize, u8, u16);
+    rev!(try_from_unbounded, usize, u16);
     rev!(try_from_upper_bounded, usize, u32, u64, u128);
     rev!(try_from_lower_bounded, usize, i8, i16);
     rev!(try_from_both_bounded, usize, i32, i64, i128);
 
     rev!(try_from_unbounded, isize, u8);
     rev!(try_from_upper_bounded, isize, u16, u32, u64, u128);
-    rev!(try_from_unbounded, isize, i8, i16);
+    rev!(try_from_unbounded, isize, i16);
     rev!(try_from_both_bounded, isize, i32, i64, i128);
 }
 
 #[cfg(target_pointer_width = "32")]
 mod ptr_try_from_impls {
     use super::TryFromIntError;
-    use convert::TryFrom;
+    use convert::{Infallible, TryFrom};
 
     try_from_upper_bounded!(usize, u8, u16);
     try_from_unbounded!(usize, u32, u64, u128);
@@ -2677,21 +2669,21 @@ mod ptr_try_from_impls {
     try_from_both_bounded!(isize, i8, i16);
     try_from_unbounded!(isize, i32, i64, i128);
 
-    rev!(try_from_unbounded, usize, u8, u16, u32);
+    rev!(try_from_unbounded, usize, u16, u32);
     rev!(try_from_upper_bounded, usize, u64, u128);
     rev!(try_from_lower_bounded, usize, i8, i16, i32);
     rev!(try_from_both_bounded, usize, i64, i128);
 
     rev!(try_from_unbounded, isize, u8, u16);
     rev!(try_from_upper_bounded, isize, u32, u64, u128);
-    rev!(try_from_unbounded, isize, i8, i16, i32);
+    rev!(try_from_unbounded, isize, i16, i32);
     rev!(try_from_both_bounded, isize, i64, i128);
 }
 
 #[cfg(target_pointer_width = "64")]
 mod ptr_try_from_impls {
     use super::TryFromIntError;
-    use convert::TryFrom;
+    use convert::{Infallible, TryFrom};
 
     try_from_upper_bounded!(usize, u8, u16, u32);
     try_from_unbounded!(usize, u64, u128);
@@ -2703,14 +2695,14 @@ mod ptr_try_from_impls {
     try_from_both_bounded!(isize, i8, i16, i32);
     try_from_unbounded!(isize, i64, i128);
 
-    rev!(try_from_unbounded, usize, u8, u16, u32, u64);
+    rev!(try_from_unbounded, usize, u16, u32, u64);
     rev!(try_from_upper_bounded, usize, u128);
     rev!(try_from_lower_bounded, usize, i8, i16, i32, i64);
     rev!(try_from_both_bounded, usize, i128);
 
     rev!(try_from_unbounded, isize, u8, u16, u32);
     rev!(try_from_upper_bounded, isize, u64, u128);
-    rev!(try_from_unbounded, isize, i8, i16, i32, i64);
+    rev!(try_from_unbounded, isize, i16, i32, i64);
     rev!(try_from_both_bounded, isize, i128);
 }
 
diff --git a/src/libcore/num/wrapping.rs b/src/libcore/num/wrapping.rs
index acdf685e850..ae1b0b3ce11 100644
--- a/src/libcore/num/wrapping.rs
+++ b/src/libcore/num/wrapping.rs
@@ -36,6 +36,7 @@ macro_rules! sh_impl_signed {
                 *self = *self << other;
             }
         }
+        forward_ref_op_assign! { impl ShlAssign, shl_assign for Wrapping<$t>, $f }
 
         #[stable(feature = "rust1", since = "1.0.0")]
         impl Shr<$f> for Wrapping<$t> {
@@ -58,6 +59,7 @@ macro_rules! sh_impl_signed {
                 *self = *self >> other;
             }
         }
+        forward_ref_op_assign! { impl ShrAssign, shr_assign for Wrapping<$t>, $f }
     )
 }
 
@@ -80,6 +82,7 @@ macro_rules! sh_impl_unsigned {
                 *self = *self << other;
             }
         }
+        forward_ref_op_assign! { impl ShlAssign, shl_assign for Wrapping<$t>, $f }
 
         #[stable(feature = "rust1", since = "1.0.0")]
         impl Shr<$f> for Wrapping<$t> {
@@ -98,6 +101,7 @@ macro_rules! sh_impl_unsigned {
                 *self = *self >> other;
             }
         }
+        forward_ref_op_assign! { impl ShrAssign, shr_assign for Wrapping<$t>, $f }
     )
 }
 
@@ -142,6 +146,7 @@ macro_rules! wrapping_impl {
                 *self = *self + other;
             }
         }
+        forward_ref_op_assign! { impl AddAssign, add_assign for Wrapping<$t>, Wrapping<$t> }
 
         #[stable(feature = "rust1", since = "1.0.0")]
         impl Sub for Wrapping<$t> {
@@ -162,6 +167,7 @@ macro_rules! wrapping_impl {
                 *self = *self - other;
             }
         }
+        forward_ref_op_assign! { impl SubAssign, sub_assign for Wrapping<$t>, Wrapping<$t> }
 
         #[stable(feature = "rust1", since = "1.0.0")]
         impl Mul for Wrapping<$t> {
@@ -182,6 +188,7 @@ macro_rules! wrapping_impl {
                 *self = *self * other;
             }
         }
+        forward_ref_op_assign! { impl MulAssign, mul_assign for Wrapping<$t>, Wrapping<$t> }
 
         #[stable(feature = "wrapping_div", since = "1.3.0")]
         impl Div for Wrapping<$t> {
@@ -202,6 +209,7 @@ macro_rules! wrapping_impl {
                 *self = *self / other;
             }
         }
+        forward_ref_op_assign! { impl DivAssign, div_assign for Wrapping<$t>, Wrapping<$t> }
 
         #[stable(feature = "wrapping_impls", since = "1.7.0")]
         impl Rem for Wrapping<$t> {
@@ -222,6 +230,7 @@ macro_rules! wrapping_impl {
                 *self = *self % other;
             }
         }
+        forward_ref_op_assign! { impl RemAssign, rem_assign for Wrapping<$t>, Wrapping<$t> }
 
         #[stable(feature = "rust1", since = "1.0.0")]
         impl Not for Wrapping<$t> {
@@ -254,6 +263,7 @@ macro_rules! wrapping_impl {
                 *self = *self ^ other;
             }
         }
+        forward_ref_op_assign! { impl BitXorAssign, bitxor_assign for Wrapping<$t>, Wrapping<$t> }
 
         #[stable(feature = "rust1", since = "1.0.0")]
         impl BitOr for Wrapping<$t> {
@@ -274,6 +284,7 @@ macro_rules! wrapping_impl {
                 *self = *self | other;
             }
         }
+        forward_ref_op_assign! { impl BitOrAssign, bitor_assign for Wrapping<$t>, Wrapping<$t> }
 
         #[stable(feature = "rust1", since = "1.0.0")]
         impl BitAnd for Wrapping<$t> {
@@ -294,6 +305,7 @@ macro_rules! wrapping_impl {
                 *self = *self & other;
             }
         }
+        forward_ref_op_assign! { impl BitAndAssign, bitand_assign for Wrapping<$t>, Wrapping<$t> }
 
         #[stable(feature = "wrapping_neg", since = "1.10.0")]
         impl Neg for Wrapping<$t> {
diff --git a/src/libcore/ops/arith.rs b/src/libcore/ops/arith.rs
index 62007caedd3..8b3d662a6db 100644
--- a/src/libcore/ops/arith.rs
+++ b/src/libcore/ops/arith.rs
@@ -662,6 +662,8 @@ macro_rules! add_assign_impl {
             #[rustc_inherit_overflow_checks]
             fn add_assign(&mut self, other: $t) { *self += other }
         }
+
+        forward_ref_op_assign! { impl AddAssign, add_assign for $t, $t }
     )+)
 }
 
@@ -713,6 +715,8 @@ macro_rules! sub_assign_impl {
             #[rustc_inherit_overflow_checks]
             fn sub_assign(&mut self, other: $t) { *self -= other }
         }
+
+        forward_ref_op_assign! { impl SubAssign, sub_assign for $t, $t }
     )+)
 }
 
@@ -755,6 +759,8 @@ macro_rules! mul_assign_impl {
             #[rustc_inherit_overflow_checks]
             fn mul_assign(&mut self, other: $t) { *self *= other }
         }
+
+        forward_ref_op_assign! { impl MulAssign, mul_assign for $t, $t }
     )+)
 }
 
@@ -796,6 +802,8 @@ macro_rules! div_assign_impl {
             #[inline]
             fn div_assign(&mut self, other: $t) { *self /= other }
         }
+
+        forward_ref_op_assign! { impl DivAssign, div_assign for $t, $t }
     )+)
 }
 
@@ -841,6 +849,8 @@ macro_rules! rem_assign_impl {
             #[inline]
             fn rem_assign(&mut self, other: $t) { *self %= other }
         }
+
+        forward_ref_op_assign! { impl RemAssign, rem_assign for $t, $t }
     )+)
 }
 
diff --git a/src/libcore/ops/bit.rs b/src/libcore/ops/bit.rs
index 0bc5e554cb3..7ac5fc4debf 100644
--- a/src/libcore/ops/bit.rs
+++ b/src/libcore/ops/bit.rs
@@ -593,6 +593,8 @@ macro_rules! bitand_assign_impl {
             #[inline]
             fn bitand_assign(&mut self, other: $t) { *self &= other }
         }
+
+        forward_ref_op_assign! { impl BitAndAssign, bitand_assign for $t, $t }
     )+)
 }
 
@@ -638,6 +640,8 @@ macro_rules! bitor_assign_impl {
             #[inline]
             fn bitor_assign(&mut self, other: $t) { *self |= other }
         }
+
+        forward_ref_op_assign! { impl BitOrAssign, bitor_assign for $t, $t }
     )+)
 }
 
@@ -683,6 +687,8 @@ macro_rules! bitxor_assign_impl {
             #[inline]
             fn bitxor_assign(&mut self, other: $t) { *self ^= other }
         }
+
+        forward_ref_op_assign! { impl BitXorAssign, bitxor_assign for $t, $t }
     )+)
 }
 
@@ -729,6 +735,8 @@ macro_rules! shl_assign_impl {
                 *self <<= other
             }
         }
+
+        forward_ref_op_assign! { impl ShlAssign, shl_assign for $t, $f }
     )
 }
 
@@ -793,6 +801,8 @@ macro_rules! shr_assign_impl {
                 *self >>= other
             }
         }
+
+        forward_ref_op_assign! { impl ShrAssign, shr_assign for $t, $f }
     )
 }
 
diff --git a/src/libcore/ops/range.rs b/src/libcore/ops/range.rs
index 463a50491a8..3f573f7c7eb 100644
--- a/src/libcore/ops/range.rs
+++ b/src/libcore/ops/range.rs
@@ -241,9 +241,9 @@ impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
     }
 }
 
-/// An range bounded inclusively below and above (`start...end`).
+/// An range bounded inclusively below and above (`start..=end`).
 ///
-/// The `RangeInclusive` `start...end` contains all values with `x >= start`
+/// The `RangeInclusive` `start..=end` contains all values with `x >= start`
 /// and `x <= end`.
 ///
 /// # Examples
@@ -251,12 +251,12 @@ impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
 /// ```
 /// #![feature(inclusive_range,inclusive_range_syntax)]
 ///
-/// assert_eq!((3...5), std::ops::RangeInclusive { start: 3, end: 5 });
-/// assert_eq!(3 + 4 + 5, (3...5).sum());
+/// assert_eq!((3..=5), std::ops::RangeInclusive { start: 3, end: 5 });
+/// assert_eq!(3 + 4 + 5, (3..=5).sum());
 ///
 /// let arr = [0, 1, 2, 3];
-/// assert_eq!(arr[ ...2], [0,1,2  ]);
-/// assert_eq!(arr[1...2], [  1,2  ]);  // RangeInclusive
+/// assert_eq!(arr[ ..=2], [0,1,2  ]);
+/// assert_eq!(arr[1..=2], [  1,2  ]);  // RangeInclusive
 /// ```
 #[derive(Clone, PartialEq, Eq, Hash)]  // not Copy -- see #27186
 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
@@ -276,7 +276,7 @@ pub struct RangeInclusive<Idx> {
 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
 impl<Idx: fmt::Debug> fmt::Debug for RangeInclusive<Idx> {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-        write!(fmt, "{:?}...{:?}", self.start, self.end)
+        write!(fmt, "{:?}..={:?}", self.start, self.end)
     }
 }
 
@@ -289,32 +289,32 @@ impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
     /// ```
     /// #![feature(range_contains,inclusive_range_syntax)]
     ///
-    /// assert!(!(3...5).contains(2));
-    /// assert!( (3...5).contains(3));
-    /// assert!( (3...5).contains(4));
-    /// assert!( (3...5).contains(5));
-    /// assert!(!(3...5).contains(6));
+    /// assert!(!(3..=5).contains(2));
+    /// assert!( (3..=5).contains(3));
+    /// assert!( (3..=5).contains(4));
+    /// assert!( (3..=5).contains(5));
+    /// assert!(!(3..=5).contains(6));
     ///
-    /// assert!( (3...3).contains(3));
-    /// assert!(!(3...2).contains(3));
+    /// assert!( (3..=3).contains(3));
+    /// assert!(!(3..=2).contains(3));
     /// ```
     pub fn contains(&self, item: Idx) -> bool {
         self.start <= item && item <= self.end
     }
 }
 
-/// A range only bounded inclusively above (`...end`).
+/// A range only bounded inclusively above (`..=end`).
 ///
-/// The `RangeToInclusive` `...end` contains all values with `x <= end`.
+/// The `RangeToInclusive` `..=end` contains all values with `x <= end`.
 /// It cannot serve as an [`Iterator`] because it doesn't have a starting point.
 ///
 /// # Examples
 ///
-/// The `...end` syntax is a `RangeToInclusive`:
+/// The `..=end` syntax is a `RangeToInclusive`:
 ///
 /// ```
 /// #![feature(inclusive_range,inclusive_range_syntax)]
-/// assert_eq!((...5), std::ops::RangeToInclusive{ end: 5 });
+/// assert_eq!((..=5), std::ops::RangeToInclusive{ end: 5 });
 /// ```
 ///
 /// It does not have an [`IntoIterator`] implementation, so you can't use it in a
@@ -325,7 +325,7 @@ impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
 ///
 /// // error[E0277]: the trait bound `std::ops::RangeToInclusive<{integer}>:
 /// // std::iter::Iterator` is not satisfied
-/// for i in ...5 {
+/// for i in ..=5 {
 ///     // ...
 /// }
 /// ```
@@ -337,8 +337,8 @@ impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
 /// #![feature(inclusive_range_syntax)]
 ///
 /// let arr = [0, 1, 2, 3];
-/// assert_eq!(arr[ ...2], [0,1,2  ]);  // RangeToInclusive
-/// assert_eq!(arr[1...2], [  1,2  ]);
+/// assert_eq!(arr[ ..=2], [0,1,2  ]);  // RangeToInclusive
+/// assert_eq!(arr[1..=2], [  1,2  ]);
 /// ```
 ///
 /// [`IntoIterator`]: ../iter/trait.Iterator.html
@@ -357,7 +357,7 @@ pub struct RangeToInclusive<Idx> {
 #[unstable(feature = "inclusive_range", reason = "recently added, follows RFC", issue = "28237")]
 impl<Idx: fmt::Debug> fmt::Debug for RangeToInclusive<Idx> {
     fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
-        write!(fmt, "...{:?}", self.end)
+        write!(fmt, "..={:?}", self.end)
     }
 }
 
@@ -370,9 +370,9 @@ impl<Idx: PartialOrd<Idx>> RangeToInclusive<Idx> {
     /// ```
     /// #![feature(range_contains,inclusive_range_syntax)]
     ///
-    /// assert!( (...5).contains(-1_000_000_000));
-    /// assert!( (...5).contains(5));
-    /// assert!(!(...5).contains(6));
+    /// assert!( (..=5).contains(-1_000_000_000));
+    /// assert!( (..=5).contains(5));
+    /// assert!(!(..=5).contains(6));
     /// ```
     pub fn contains(&self, item: Idx) -> bool {
         (item <= self.end)
diff --git a/src/libcore/ops/unsize.rs b/src/libcore/ops/unsize.rs
index 58da290cfb6..cd896859b16 100644
--- a/src/libcore/ops/unsize.rs
+++ b/src/libcore/ops/unsize.rs
@@ -42,7 +42,7 @@ use marker::Unsize;
 /// [unsize]: ../marker/trait.Unsize.html
 /// [nomicon-coerce]: ../../nomicon/coercions.html
 #[unstable(feature = "coerce_unsized", issue = "27732")]
-#[lang="coerce_unsized"]
+#[lang = "coerce_unsized"]
 pub trait CoerceUnsized<T> {
     // Empty.
 }
diff --git a/src/libcore/option.rs b/src/libcore/option.rs
index 138e04c7737..980ea551f08 100644
--- a/src/libcore/option.rs
+++ b/src/libcore/option.rs
@@ -146,7 +146,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use iter::{FromIterator, FusedIterator, TrustedLen};
-use mem;
+use {mem, ops};
 
 // Note that this is not a lang item per se, but it has a hidden dependency on
 // `Iterator`, which is one. The compiler assumes that the `next` method of
@@ -1123,3 +1123,29 @@ impl<A, V: FromIterator<A>> FromIterator<Option<A>> for Option<V> {
         }
     }
 }
+
+/// The error type that results from applying the try operator (`?`) to a `None` value. If you wish
+/// to allow `x?` (where `x` is an `Option<T>`) to be converted into your error type, you can
+/// implement `impl From<NoneError>` for `YourErrorType`. In that case, `x?` within a function that
+/// returns `Result<_, YourErrorType>` will translate a `None` value into an `Err` result.
+#[unstable(feature = "try_trait", issue = "42327")]
+#[derive(Clone, Copy, PartialEq, PartialOrd, Eq, Ord, Debug, Hash)]
+pub struct NoneError;
+
+#[unstable(feature = "try_trait", issue = "42327")]
+impl<T> ops::Try for Option<T> {
+    type Ok = T;
+    type Error = NoneError;
+
+    fn into_result(self) -> Result<T, NoneError> {
+        self.ok_or(NoneError)
+    }
+
+    fn from_ok(v: T) -> Self {
+        Some(v)
+    }
+
+    fn from_error(_: NoneError) -> Self {
+        None
+    }
+}
diff --git a/src/libcore/ptr.rs b/src/libcore/ptr.rs
index 4041a3760e5..34d31044653 100644
--- a/src/libcore/ptr.rs
+++ b/src/libcore/ptr.rs
@@ -56,7 +56,7 @@ pub use intrinsics::write_bytes;
 /// This has all the same safety problems as `ptr::read` with respect to
 /// invalid pointers, types, and double drops.
 #[stable(feature = "drop_in_place", since = "1.8.0")]
-#[lang="drop_in_place"]
+#[lang = "drop_in_place"]
 #[allow(unconditional_recursion)]
 pub unsafe fn drop_in_place<T: ?Sized>(to_drop: *mut T) {
     // Code here does not matter - this is replaced by the
diff --git a/src/libcore/slice/mod.rs b/src/libcore/slice/mod.rs
index dacc014955a..ae243f3f246 100644
--- a/src/libcore/slice/mod.rs
+++ b/src/libcore/slice/mod.rs
@@ -16,6 +16,9 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+// FIXME: after next stage0, change RangeInclusive { ... } back to ..=
+use ops::RangeInclusive;
+
 // How this module is organized.
 //
 // The library infrastructure for slices is fairly messy. There's
@@ -1044,32 +1047,32 @@ impl<T> SliceIndex<[T]> for ops::RangeToInclusive<usize> {
 
     #[inline]
     fn get(self, slice: &[T]) -> Option<&[T]> {
-        (0...self.end).get(slice)
+        (RangeInclusive { start: 0, end: self.end }).get(slice)
     }
 
     #[inline]
     fn get_mut(self, slice: &mut [T]) -> Option<&mut [T]> {
-        (0...self.end).get_mut(slice)
+        (RangeInclusive { start: 0, end: self.end }).get_mut(slice)
     }
 
     #[inline]
     unsafe fn get_unchecked(self, slice: &[T]) -> &[T] {
-        (0...self.end).get_unchecked(slice)
+        (RangeInclusive { start: 0, end: self.end }).get_unchecked(slice)
     }
 
     #[inline]
     unsafe fn get_unchecked_mut(self, slice: &mut [T]) -> &mut [T] {
-        (0...self.end).get_unchecked_mut(slice)
+        (RangeInclusive { start: 0, end: self.end }).get_unchecked_mut(slice)
     }
 
     #[inline]
     fn index(self, slice: &[T]) -> &[T] {
-        (0...self.end).index(slice)
+        (RangeInclusive { start: 0, end: self.end }).index(slice)
     }
 
     #[inline]
     fn index_mut(self, slice: &mut [T]) -> &mut [T] {
-        (0...self.end).index_mut(slice)
+        (RangeInclusive { start: 0, end: self.end }).index_mut(slice)
     }
 }
 
diff --git a/src/libcore/str/mod.rs b/src/libcore/str/mod.rs
index c24cdb30bad..0af9fcf0a3d 100644
--- a/src/libcore/str/mod.rs
+++ b/src/libcore/str/mod.rs
@@ -18,9 +18,9 @@ use self::pattern::Pattern;
 use self::pattern::{Searcher, ReverseSearcher, DoubleEndedSearcher};
 
 use char;
-use convert::TryFrom;
 use fmt;
-use iter::{Map, Cloned, FusedIterator};
+use iter::{Map, Cloned, FusedIterator, TrustedLen};
+use iter_private::TrustedRandomAccess;
 use slice::{self, SliceIndex};
 use mem;
 
@@ -818,6 +818,17 @@ impl<'a> ExactSizeIterator for Bytes<'a> {
 #[unstable(feature = "fused", issue = "35602")]
 impl<'a> FusedIterator for Bytes<'a> {}
 
+#[unstable(feature = "trusted_len", issue = "37572")]
+unsafe impl<'a> TrustedLen for Bytes<'a> {}
+
+#[doc(hidden)]
+unsafe impl<'a> TrustedRandomAccess for Bytes<'a> {
+    unsafe fn get_unchecked(&mut self, i: usize) -> u8 {
+        self.0.get_unchecked(i)
+    }
+    fn may_have_side_effect() -> bool { false }
+}
+
 /// This macro generates a Clone impl for string pattern API
 /// wrapper types of the form X<'a, P>
 macro_rules! derive_pattern_clone {
@@ -1399,9 +1410,6 @@ Section: Comparing strings
 */
 
 /// Bytewise slice equality
-/// NOTE: This function is (ab)used in rustc::middle::trans::_match
-/// to compare &[u8] byte slices that are not necessarily valid UTF-8.
-#[lang = "str_eq"]
 #[inline]
 fn eq_slice(a: &str, b: &str) -> bool {
     a.as_bytes() == b.as_bytes()
@@ -2189,7 +2197,7 @@ pub trait StrExt {
     #[stable(feature = "core", since = "1.6.0")]
     fn is_empty(&self) -> bool;
     #[stable(feature = "core", since = "1.6.0")]
-    fn parse<'a, T: TryFrom<&'a str>>(&'a self) -> Result<T, T::Error>;
+    fn parse<T: FromStr>(&self) -> Result<T, T::Err>;
 }
 
 // truncate `&str` to length at most equal to `max`
@@ -2509,9 +2517,7 @@ impl StrExt for str {
     fn is_empty(&self) -> bool { self.len() == 0 }
 
     #[inline]
-    fn parse<'a, T>(&'a self) -> Result<T, T::Error> where T: TryFrom<&'a str> {
-        T::try_from(self)
-    }
+    fn parse<T: FromStr>(&self) -> Result<T, T::Err> { FromStr::from_str(self) }
 }
 
 #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libcore/sync/atomic.rs b/src/libcore/sync/atomic.rs
index 3dd08e69710..465d31b5f49 100644
--- a/src/libcore/sync/atomic.rs
+++ b/src/libcore/sync/atomic.rs
@@ -926,10 +926,24 @@ macro_rules! atomic_int {
      $stable_cxchg:meta,
      $stable_debug:meta,
      $stable_access:meta,
+     $s_int_type:expr, $int_ref:expr,
      $int_type:ident $atomic_type:ident $atomic_init:ident) => {
         /// An integer type which can be safely shared between threads.
         ///
-        /// This type has the same in-memory representation as the underlying integer type.
+        /// This type has the same in-memory representation as the underlying
+        /// integer type, [`
+        #[doc = $s_int_type]
+        /// `](
+        #[doc = $int_ref]
+        /// ). For more about the differences between atomic types and
+        /// non-atomic types, please see the [module-level documentation].
+        ///
+        /// Please note that examples are shared between atomic variants of
+        /// primitive integer types, so it's normal that they are all
+        /// demonstrating [`AtomicIsize`].
+        ///
+        /// [module-level documentation]: index.html
+        /// [`AtomicIsize`]: struct.AtomicIsize.html
         #[$stable]
         pub struct $atomic_type {
             v: UnsafeCell<$int_type>,
@@ -1339,6 +1353,7 @@ atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
+    "i8", "../../../std/primitive.i8.html",
     i8 AtomicI8 ATOMIC_I8_INIT
 }
 #[cfg(target_has_atomic = "8")]
@@ -1348,6 +1363,7 @@ atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
+    "u8", "../../../std/primitive.u8.html",
     u8 AtomicU8 ATOMIC_U8_INIT
 }
 #[cfg(target_has_atomic = "16")]
@@ -1357,6 +1373,7 @@ atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
+    "i16", "../../../std/primitive.i16.html",
     i16 AtomicI16 ATOMIC_I16_INIT
 }
 #[cfg(target_has_atomic = "16")]
@@ -1366,6 +1383,7 @@ atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
+    "u16", "../../../std/primitive.u16.html",
     u16 AtomicU16 ATOMIC_U16_INIT
 }
 #[cfg(target_has_atomic = "32")]
@@ -1375,6 +1393,7 @@ atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
+    "i32", "../../../std/primitive.i32.html",
     i32 AtomicI32 ATOMIC_I32_INIT
 }
 #[cfg(target_has_atomic = "32")]
@@ -1384,6 +1403,7 @@ atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
+    "u32", "../../../std/primitive.u32.html",
     u32 AtomicU32 ATOMIC_U32_INIT
 }
 #[cfg(target_has_atomic = "64")]
@@ -1393,6 +1413,7 @@ atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
+    "i64", "../../../std/primitive.i64.html",
     i64 AtomicI64 ATOMIC_I64_INIT
 }
 #[cfg(target_has_atomic = "64")]
@@ -1402,6 +1423,7 @@ atomic_int! {
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
     unstable(feature = "integer_atomics", issue = "32976"),
+    "u64", "../../../std/primitive.u64.html",
     u64 AtomicU64 ATOMIC_U64_INIT
 }
 #[cfg(target_has_atomic = "ptr")]
@@ -1411,6 +1433,7 @@ atomic_int!{
     stable(feature = "extended_compare_and_swap", since = "1.10.0"),
     stable(feature = "atomic_debug", since = "1.3.0"),
     stable(feature = "atomic_access", since = "1.15.0"),
+    "isize", "../../../std/primitive.isize.html",
     isize AtomicIsize ATOMIC_ISIZE_INIT
 }
 #[cfg(target_has_atomic = "ptr")]
@@ -1420,6 +1443,7 @@ atomic_int!{
     stable(feature = "extended_compare_and_swap", since = "1.10.0"),
     stable(feature = "atomic_debug", since = "1.3.0"),
     stable(feature = "atomic_access", since = "1.15.0"),
+    "usize", "../../../std/primitive.usize.html",
     usize AtomicUsize ATOMIC_USIZE_INIT
 }
 
@@ -1752,7 +1776,7 @@ pub fn fence(order: Ordering) {
 /// [`Relaxed`]: enum.Ordering.html#variant.Relaxed
 /// [memory barriers]: https://www.kernel.org/doc/Documentation/memory-barriers.txt
 #[inline]
-#[stable(feature = "compiler_fences", since = "1.22.0")]
+#[stable(feature = "compiler_fences", since = "1.21.0")]
 pub fn compiler_fence(order: Ordering) {
     unsafe {
         match order {
diff --git a/src/libcore/tests/char.rs b/src/libcore/tests/char.rs
index 7c3b90c8153..4e10ceac878 100644
--- a/src/libcore/tests/char.rs
+++ b/src/libcore/tests/char.rs
@@ -32,7 +32,6 @@ fn test_convert() {
 #[test]
 fn test_from_str() {
     assert_eq!(char::from_str("a").unwrap(), 'a');
-    assert_eq!(char::try_from("a").unwrap(), 'a');
     assert_eq!(char::from_str("\0").unwrap(), '\0');
     assert_eq!(char::from_str("\u{D7FF}").unwrap(), '\u{d7FF}');
     assert!(char::from_str("").is_err());
diff --git a/src/libcore/tests/iter.rs b/src/libcore/tests/iter.rs
index 59ae30de452..f8c6fc5c8fa 100644
--- a/src/libcore/tests/iter.rs
+++ b/src/libcore/tests/iter.rs
@@ -249,6 +249,25 @@ fn test_filter_map() {
 }
 
 #[test]
+fn test_filter_map_fold() {
+    let xs = [0, 1, 2, 3, 4, 5, 6, 7, 8];
+    let ys = [0*0, 2*2, 4*4, 6*6, 8*8];
+    let it = xs.iter().filter_map(|&x| if x % 2 == 0 { Some(x*x) } else { None });
+    let i = it.fold(0, |i, x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+
+    let it = xs.iter().filter_map(|&x| if x % 2 == 0 { Some(x*x) } else { None });
+    let i = it.rfold(ys.len(), |i, x| {
+        assert_eq!(x, ys[i - 1]);
+        i - 1
+    });
+    assert_eq!(i, 0);
+}
+
+#[test]
 fn test_iterator_enumerate() {
     let xs = [0, 1, 2, 3, 4, 5];
     let it = xs.iter().enumerate();
@@ -282,7 +301,31 @@ fn test_iterator_enumerate_nth() {
 #[test]
 fn test_iterator_enumerate_count() {
     let xs = [0, 1, 2, 3, 4, 5];
-    assert_eq!(xs.iter().count(), 6);
+    assert_eq!(xs.iter().enumerate().count(), 6);
+}
+
+#[test]
+fn test_iterator_enumerate_fold() {
+    let xs = [0, 1, 2, 3, 4, 5];
+    let mut it = xs.iter().enumerate();
+    // steal a couple to get an interesting offset
+    assert_eq!(it.next(), Some((0, &0)));
+    assert_eq!(it.next(), Some((1, &1)));
+    let i = it.fold(2, |i, (j, &x)| {
+        assert_eq!(i, j);
+        assert_eq!(x, xs[j]);
+        i + 1
+    });
+    assert_eq!(i, xs.len());
+
+    let mut it = xs.iter().enumerate();
+    assert_eq!(it.next(), Some((0, &0)));
+    let i = it.rfold(xs.len() - 1, |i, (j, &x)| {
+        assert_eq!(i, j);
+        assert_eq!(x, xs[j]);
+        i - 1
+    });
+    assert_eq!(i, 0);
 }
 
 #[test]
@@ -292,6 +335,25 @@ fn test_iterator_filter_count() {
 }
 
 #[test]
+fn test_iterator_filter_fold() {
+    let xs = [0, 1, 2, 3, 4, 5, 6, 7, 8];
+    let ys = [0, 2, 4, 6, 8];
+    let it = xs.iter().filter(|&&x| x % 2 == 0);
+    let i = it.fold(0, |i, &x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+
+    let it = xs.iter().filter(|&&x| x % 2 == 0);
+    let i = it.rfold(ys.len(), |i, &x| {
+        assert_eq!(x, ys[i - 1]);
+        i - 1
+    });
+    assert_eq!(i, 0);
+}
+
+#[test]
 fn test_iterator_peekable() {
     let xs = vec![0, 1, 2, 3, 4, 5];
     let mut it = xs.iter().cloned().peekable();
@@ -381,6 +443,18 @@ fn test_iterator_peekable_last() {
     assert_eq!(it.last(), None);
 }
 
+#[test]
+fn test_iterator_peekable_fold() {
+    let xs = [0, 1, 2, 3, 4, 5];
+    let mut it = xs.iter().peekable();
+    assert_eq!(it.peek(), Some(&&0));
+    let i = it.fold(0, |i, &x| {
+        assert_eq!(x, xs[i]);
+        i + 1
+    });
+    assert_eq!(i, xs.len());
+}
+
 /// This is an iterator that follows the Iterator contract,
 /// but it is not fused. After having returned None once, it will start
 /// producing elements if .next() is called again.
@@ -471,6 +545,26 @@ fn test_iterator_skip_while() {
 }
 
 #[test]
+fn test_iterator_skip_while_fold() {
+    let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19];
+    let ys = [15, 16, 17, 19];
+    let it = xs.iter().skip_while(|&x| *x < 15);
+    let i = it.fold(0, |i, &x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+
+    let mut it = xs.iter().skip_while(|&x| *x < 15);
+    assert_eq!(it.next(), Some(&ys[0])); // process skips before folding
+    let i = it.fold(1, |i, &x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+}
+
+#[test]
 fn test_iterator_skip() {
     let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19, 20, 30];
     let ys = [13, 15, 16, 17, 19, 20, 30];
@@ -567,6 +661,26 @@ fn test_iterator_skip_last() {
 }
 
 #[test]
+fn test_iterator_skip_fold() {
+    let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19, 20, 30];
+    let ys = [13, 15, 16, 17, 19, 20, 30];
+    let it = xs.iter().skip(5);
+    let i = it.fold(0, |i, &x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+
+    let mut it = xs.iter().skip(5);
+    assert_eq!(it.next(), Some(&ys[0])); // process skips before folding
+    let i = it.fold(1, |i, &x| {
+        assert_eq!(x, ys[i]);
+        i + 1
+    });
+    assert_eq!(i, ys.len());
+}
+
+#[test]
 fn test_iterator_take() {
     let xs = [0, 1, 2, 3, 5, 13, 15, 16, 17, 19];
     let ys = [0, 1, 2, 3, 5];
@@ -661,13 +775,22 @@ fn test_iterator_flat_map_fold() {
     let xs = [0, 3, 6];
     let ys = [1, 2, 3, 4, 5, 6, 7];
     let mut it = xs.iter().flat_map(|&x| x..x+3);
-    it.next();
-    it.next_back();
+    assert_eq!(it.next(), Some(0));
+    assert_eq!(it.next_back(), Some(8));
     let i = it.fold(0, |i, x| {
         assert_eq!(x, ys[i]);
         i + 1
     });
     assert_eq!(i, ys.len());
+
+    let mut it = xs.iter().flat_map(|&x| x..x+3);
+    assert_eq!(it.next(), Some(0));
+    assert_eq!(it.next_back(), Some(8));
+    let i = it.rfold(ys.len(), |i, x| {
+        assert_eq!(x, ys[i - 1]);
+        i - 1
+    });
+    assert_eq!(i, 0);
 }
 
 #[test]
@@ -685,6 +808,32 @@ fn test_inspect() {
 }
 
 #[test]
+fn test_inspect_fold() {
+    let xs = [1, 2, 3, 4];
+    let mut n = 0;
+    {
+        let it = xs.iter().inspect(|_| n += 1);
+        let i = it.fold(0, |i, &x| {
+            assert_eq!(x, xs[i]);
+            i + 1
+        });
+        assert_eq!(i, xs.len());
+    }
+    assert_eq!(n, xs.len());
+
+    let mut n = 0;
+    {
+        let it = xs.iter().inspect(|_| n += 1);
+        let i = it.rfold(xs.len(), |i, &x| {
+            assert_eq!(x, xs[i - 1]);
+            i - 1
+        });
+        assert_eq!(i, 0);
+    }
+    assert_eq!(n, xs.len());
+}
+
+#[test]
 fn test_cycle() {
     let cycle_len = 3;
     let it = (0..).step_by(1).take(cycle_len).cycle();
@@ -1094,21 +1243,21 @@ fn test_range() {
 
 #[test]
 fn test_range_inclusive_exhaustion() {
-    let mut r = 10...10;
+    let mut r = 10..=10;
     assert_eq!(r.next(), Some(10));
-    assert_eq!(r, 1...0);
+    assert_eq!(r, 1..=0);
 
-    let mut r = 10...10;
+    let mut r = 10..=10;
     assert_eq!(r.next_back(), Some(10));
-    assert_eq!(r, 1...0);
+    assert_eq!(r, 1..=0);
 
-    let mut r = 10...12;
+    let mut r = 10..=12;
     assert_eq!(r.nth(2), Some(12));
-    assert_eq!(r, 1...0);
+    assert_eq!(r, 1..=0);
 
-    let mut r = 10...12;
+    let mut r = 10..=12;
     assert_eq!(r.nth(5), None);
-    assert_eq!(r, 1...0);
+    assert_eq!(r, 1..=0);
 
 }
 
@@ -1145,20 +1294,20 @@ fn test_range_from_nth() {
 
 #[test]
 fn test_range_inclusive_nth() {
-    assert_eq!((10...15).nth(0), Some(10));
-    assert_eq!((10...15).nth(1), Some(11));
-    assert_eq!((10...15).nth(5), Some(15));
-    assert_eq!((10...15).nth(6), None);
+    assert_eq!((10..=15).nth(0), Some(10));
+    assert_eq!((10..=15).nth(1), Some(11));
+    assert_eq!((10..=15).nth(5), Some(15));
+    assert_eq!((10..=15).nth(6), None);
 
-    let mut r = 10_u8...20;
+    let mut r = 10_u8..=20;
     assert_eq!(r.nth(2), Some(12));
-    assert_eq!(r, 13...20);
+    assert_eq!(r, 13..=20);
     assert_eq!(r.nth(2), Some(15));
-    assert_eq!(r, 16...20);
+    assert_eq!(r, 16..=20);
     assert_eq!(r.is_empty(), false);
     assert_eq!(r.nth(10), None);
     assert_eq!(r.is_empty(), true);
-    assert_eq!(r, 1...0);  // We may not want to document/promise this detail
+    assert_eq!(r, 1..=0);  // We may not want to document/promise this detail
 }
 
 #[test]
@@ -1242,6 +1391,31 @@ fn test_fuse_count() {
 }
 
 #[test]
+fn test_fuse_fold() {
+    let xs = [0, 1, 2];
+    let it = xs.iter(); // `FusedIterator`
+    let i = it.fuse().fold(0, |i, &x| {
+        assert_eq!(x, xs[i]);
+        i + 1
+    });
+    assert_eq!(i, xs.len());
+
+    let it = xs.iter(); // `FusedIterator`
+    let i = it.fuse().rfold(xs.len(), |i, &x| {
+        assert_eq!(x, xs[i - 1]);
+        i - 1
+    });
+    assert_eq!(i, 0);
+
+    let it = xs.iter().scan((), |_, &x| Some(x)); // `!FusedIterator`
+    let i = it.fuse().fold(0, |i, x| {
+        assert_eq!(x, xs[i]);
+        i + 1
+    });
+    assert_eq!(i, xs.len());
+}
+
+#[test]
 fn test_once() {
     let mut it = once(42);
     assert_eq!(it.next(), Some(42));
diff --git a/src/libcore/tests/lib.rs b/src/libcore/tests/lib.rs
index 47995597a0a..afc5de7b0ee 100644
--- a/src/libcore/tests/lib.rs
+++ b/src/libcore/tests/lib.rs
@@ -25,6 +25,7 @@
 #![feature(inclusive_range)]
 #![feature(inclusive_range_syntax)]
 #![feature(iter_rfind)]
+#![feature(iter_rfold)]
 #![feature(nonzero)]
 #![feature(rand)]
 #![feature(raw)]
@@ -38,6 +39,7 @@
 #![feature(test)]
 #![feature(trusted_len)]
 #![feature(try_from)]
+#![feature(try_trait)]
 #![feature(unique)]
 
 #![feature(const_atomic_bool_new)]
diff --git a/src/libcore/tests/num/mod.rs b/src/libcore/tests/num/mod.rs
index 400d53ce51a..7eb5ff98857 100644
--- a/src/libcore/tests/num/mod.rs
+++ b/src/libcore/tests/num/mod.rs
@@ -8,10 +8,11 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-use core::convert::TryFrom;
+use core::convert::{TryFrom, TryInto};
 use core::cmp::PartialEq;
 use core::fmt::Debug;
 use core::marker::Copy;
+use core::num::TryFromIntError;
 use core::ops::{Add, Sub, Mul, Div, Rem};
 use core::option::Option;
 use core::option::Option::{Some, None};
@@ -134,6 +135,13 @@ fn test_empty() {
     assert_eq!("".parse::<u8>().ok(), None);
 }
 
+#[test]
+fn test_infallible_try_from_int_error() {
+    let func = |x: i8| -> Result<i32, TryFromIntError> { Ok(x.try_into()?) };
+
+    assert!(func(0).is_ok());
+}
+
 macro_rules! test_impl_from {
     ($fn_name: ident, $Small: ty, $Large: ty) => {
         #[test]
diff --git a/src/libcore/tests/option.rs b/src/libcore/tests/option.rs
index 6bac55575fb..22109e28edd 100644
--- a/src/libcore/tests/option.rs
+++ b/src/libcore/tests/option.rs
@@ -270,3 +270,30 @@ fn test_cloned() {
     assert_eq!(opt_ref_ref.clone().cloned(), Some(&val));
     assert_eq!(opt_ref_ref.cloned().cloned(), Some(1));
 }
+
+#[test]
+fn test_try() {
+    fn try_option_some() -> Option<u8> {
+        let val = Some(1)?;
+        Some(val)
+    }
+    assert_eq!(try_option_some(), Some(1));
+
+    fn try_option_none() -> Option<u8> {
+        let val = None?;
+        Some(val)
+    }
+    assert_eq!(try_option_none(), None);
+
+    fn try_option_ok() -> Result<u8, NoneError> {
+        let val = Some(1)?;
+        Ok(val)
+    }
+    assert_eq!(try_option_ok(), Ok(1));
+
+    fn try_option_err() -> Result<u8, NoneError> {
+        let val = None?;
+        Ok(val)
+    }
+    assert_eq!(try_option_err(), Err(NoneError));
+}
diff --git a/src/libcore/tests/result.rs b/src/libcore/tests/result.rs
index 4c5f19dee12..ce41bde8342 100644
--- a/src/libcore/tests/result.rs
+++ b/src/libcore/tests/result.rs
@@ -8,6 +8,8 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
+use core::option::*;
+
 fn op1() -> Result<isize, &'static str> { Ok(666) }
 fn op2() -> Result<isize, &'static str> { Err("sadface") }
 
@@ -202,3 +204,30 @@ pub fn test_unwrap_or_default() {
     assert_eq!(op1().unwrap_or_default(), 666);
     assert_eq!(op2().unwrap_or_default(), 0);
 }
+
+#[test]
+fn test_try() {
+    fn try_result_some() -> Option<u8> {
+        let val = Ok(1)?;
+        Some(val)
+    }
+    assert_eq!(try_result_some(), Some(1));
+
+    fn try_result_none() -> Option<u8> {
+        let val = Err(NoneError)?;
+        Some(val)
+    }
+    assert_eq!(try_result_none(), None);
+
+    fn try_result_ok() -> Result<u8, u8> {
+        let val = Ok(1)?;
+        Ok(val)
+    }
+    assert_eq!(try_result_ok(), Ok(1));
+
+    fn try_result_err() -> Result<u8, u8> {
+        let val = Err(1)?;
+        Ok(val)
+    }
+    assert_eq!(try_result_err(), Err(1));
+}