Add a FusedIterator trait.

This trait can be used to avoid the overhead of a fuse wrapper when an iterator
is already well-behaved.

Conforming to: RFC 1581
Closes: #35602

src/liballoc/boxed.rs

@@ -61,6 +61,7 @@ use core::borrow;
 use core::cmp::Ordering;
 use core::fmt;
 use core::hash::{self, Hash};
+use core::iter::FusedIterator;
 use core::marker::{self, Unsize};
 use core::mem;
 use core::ops::{CoerceUnsized, Deref, DerefMut};
@@ -529,6 +530,9 @@ impl<I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for Box<I> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<I> {}
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<I: FusedIterator + ?Sized> FusedIterator for Box<I> {}
+
 
 /// `FnBox` is a version of the `FnOnce` intended for use with boxed
 /// closure objects. The idea is that where one would normally store a

src/liballoc/lib.rs

@@ -91,7 +91,7 @@
 #![feature(unsafe_no_drop_flag, filling_drop)]
 #![feature(unsize)]
 
-#![cfg_attr(not(test), feature(raw, fn_traits, placement_new_protocol))]
+#![cfg_attr(not(test), feature(fused, raw, fn_traits, placement_new_protocol))]
 #![cfg_attr(test, feature(test, box_heap))]
 
 // Allow testing this library

src/libcollections/binary_heap.rs

@@ -152,7 +152,7 @@
 #![stable(feature = "rust1", since = "1.0.0")]
 
 use core::ops::{Drop, Deref, DerefMut};
-use core::iter::FromIterator;
+use core::iter::{FromIterator, FusedIterator};
 use core::mem::swap;
 use core::mem::size_of;
 use core::ptr;
@@ -981,6 +981,9 @@ impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T> ExactSizeIterator for Iter<'a, T> {}
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T> FusedIterator for Iter<'a, T> {}
+
 /// An iterator that moves out of a `BinaryHeap`.
 #[stable(feature = "rust1", since = "1.0.0")]
 #[derive(Clone)]
@@ -1014,6 +1017,9 @@ impl<T> DoubleEndedIterator for IntoIter<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> ExactSizeIterator for IntoIter<T> {}
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<T> FusedIterator for IntoIter<T> {}
+
 /// An iterator that drains a `BinaryHeap`.
 #[stable(feature = "drain", since = "1.6.0")]
 pub struct Drain<'a, T: 'a> {
@@ -1046,6 +1052,9 @@ impl<'a, T: 'a> DoubleEndedIterator for Drain<'a, T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T: 'a> ExactSizeIterator for Drain<'a, T> {}
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T: 'a> FusedIterator for Drain<'a, T> {}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T: Ord> From<Vec<T>> for BinaryHeap<T> {
     fn from(vec: Vec<T>) -> BinaryHeap<T> {

src/libcollections/btree/map.rs

@@ -11,7 +11,7 @@
 use core::cmp::Ordering;
 use core::fmt::Debug;
 use core::hash::{Hash, Hasher};
-use core::iter::{FromIterator, Peekable};
+use core::iter::{FromIterator, Peekable, FusedIterator};
 use core::marker::PhantomData;
 use core::ops::Index;
 use core::{fmt, intrinsics, mem, ptr};
@@ -1147,6 +1147,9 @@ impl<'a, K: 'a, V: 'a> Iterator for Iter<'a, K, V> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for Iter<'a, K, V> {}
+
 impl<'a, K: 'a, V: 'a> DoubleEndedIterator for Iter<'a, K, V> {
     fn next_back(&mut self) -> Option<(&'a K, &'a V)> {
         if self.length == 0 {
@@ -1216,6 +1219,9 @@ impl<'a, K: 'a, V: 'a> ExactSizeIterator for IterMut<'a, K, V> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for IterMut<'a, K, V> {}
+
 impl<K, V> IntoIterator for BTreeMap<K, V> {
     type Item = (K, V);
     type IntoIter = IntoIter<K, V>;
@@ -1338,6 +1344,9 @@ impl<K, V> ExactSizeIterator for IntoIter<K, V> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<K, V> FusedIterator for IntoIter<K, V> {}
+
 impl<'a, K, V> Iterator for Keys<'a, K, V> {
     type Item = &'a K;
 
@@ -1362,6 +1371,9 @@ impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for Keys<'a, K, V> {}
+
 impl<'a, K, V> Clone for Keys<'a, K, V> {
     fn clone(&self) -> Keys<'a, K, V> {
         Keys { inner: self.inner.clone() }
@@ -1392,6 +1404,9 @@ impl<'a, K, V> ExactSizeIterator for Values<'a, K, V> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for Values<'a, K, V> {}
+
 impl<'a, K, V> Clone for Values<'a, K, V> {
     fn clone(&self) -> Values<'a, K, V> {
         Values { inner: self.inner.clone() }
@@ -1437,6 +1452,10 @@ 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> {}
+
+
 impl<'a, K, V> Range<'a, K, V> {
     unsafe fn next_unchecked(&mut self) -> (&'a K, &'a V) {
         let handle = self.front;
@@ -1511,6 +1530,9 @@ impl<'a, K, V> Range<'a, K, V> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for Range<'a, K, V> {}
+
 impl<'a, K, V> Clone for Range<'a, K, V> {
     fn clone(&self) -> Range<'a, K, V> {
         Range {
@@ -1574,6 +1596,9 @@ impl<'a, K, V> DoubleEndedIterator for RangeMut<'a, K, V> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, K, V> FusedIterator for RangeMut<'a, K, V> {}
+
 impl<'a, K, V> RangeMut<'a, K, V> {
     unsafe fn next_back_unchecked(&mut self) -> (&'a K, &'a mut V) {
         let handle = ptr::read(&self.back);

src/libcollections/btree/set.rs

@@ -15,7 +15,7 @@ use core::cmp::Ordering::{self, Less, Greater, Equal};
 use core::cmp::{min, max};
 use core::fmt::Debug;
 use core::fmt;
-use core::iter::{Peekable, FromIterator};
+use core::iter::{Peekable, FromIterator, FusedIterator};
 use core::ops::{BitOr, BitAnd, BitXor, Sub};
 
 use borrow::Borrow;
@@ -805,6 +805,8 @@ impl<'a, T> ExactSizeIterator for Iter<'a, T> {
     fn len(&self) -> usize { self.iter.len() }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T> FusedIterator for Iter<'a, T> {}
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> Iterator for IntoIter<T> {
@@ -828,6 +830,8 @@ impl<T> ExactSizeIterator for IntoIter<T> {
     fn len(&self) -> usize { self.iter.len() }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<T> FusedIterator for IntoIter<T> {}
 
 impl<'a, T> Clone for Range<'a, T> {
     fn clone(&self) -> Range<'a, T> {
@@ -847,6 +851,9 @@ impl<'a, T> DoubleEndedIterator for Range<'a, T> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T> FusedIterator for Range<'a, T> {}
+
 /// Compare `x` and `y`, but return `short` if x is None and `long` if y is None
 fn cmp_opt<T: Ord>(x: Option<&T>, y: Option<&T>, short: Ordering, long: Ordering) -> Ordering {
     match (x, y) {
@@ -890,6 +897,9 @@ impl<'a, T: Ord> Iterator for Difference<'a, T> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T: Ord> FusedIterator for Difference<'a, T> {}
+
 impl<'a, T> Clone for SymmetricDifference<'a, T> {
     fn clone(&self) -> SymmetricDifference<'a, T> {
         SymmetricDifference {
@@ -920,6 +930,9 @@ impl<'a, T: Ord> Iterator for SymmetricDifference<'a, T> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T: Ord> FusedIterator for SymmetricDifference<'a, T> {}
+
 impl<'a, T> Clone for Intersection<'a, T> {
     fn clone(&self) -> Intersection<'a, T> {
         Intersection {
@@ -960,6 +973,9 @@ impl<'a, T: Ord> Iterator for Intersection<'a, T> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T: Ord> FusedIterator for Intersection<'a, T> {}
+
 impl<'a, T> Clone for Union<'a, T> {
     fn clone(&self) -> Union<'a, T> {
         Union {
@@ -991,3 +1007,6 @@ impl<'a, T: Ord> Iterator for Union<'a, T> {
         (max(a_len, b_len), Some(a_len + b_len))
     }
 }
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T: Ord> FusedIterator for Union<'a, T> {}

src/libcollections/enum_set.rs

@@ -20,7 +20,7 @@
 
 use core::marker;
 use core::fmt;
-use core::iter::FromIterator;
+use core::iter::{FromIterator, FusedIterator};
 use core::ops::{Sub, BitOr, BitAnd, BitXor};
 
 // FIXME(contentions): implement union family of methods? (general design may be
@@ -266,6 +266,9 @@ impl<E: CLike> Iterator for Iter<E> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<E: CLike> FusedIterator for Iter<E> {}
+
 impl<E: CLike> FromIterator<E> for EnumSet<E> {
     fn from_iter<I: IntoIterator<Item = E>>(iter: I) -> EnumSet<E> {
         let mut ret = EnumSet::new();

src/libcollections/lib.rs

@@ -37,6 +37,7 @@
 #![feature(core_intrinsics)]
 #![feature(dropck_parametricity)]
 #![feature(fmt_internals)]
+#![feature(fused)]
 #![feature(heap_api)]
 #![feature(inclusive_range)]
 #![feature(lang_items)]

src/libcollections/linked_list.rs

@@ -19,7 +19,7 @@ use alloc::boxed::{Box, IntermediateBox};
 use core::cmp::Ordering;
 use core::fmt;
 use core::hash::{Hasher, Hash};
-use core::iter::FromIterator;
+use core::iter::{FromIterator, FusedIterator};
 use core::marker::PhantomData;
 use core::mem;
 use core::ops::{BoxPlace, InPlace, Place, Placer};
@@ -757,6 +757,9 @@ impl<'a, T> DoubleEndedIterator for Iter<'a, T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T> ExactSizeIterator for Iter<'a, T> {}
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T> FusedIterator for Iter<'a, T> {}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T> Iterator for IterMut<'a, T> {
     type Item = &'a mut T;
@@ -801,6 +804,9 @@ impl<'a, T> DoubleEndedIterator for IterMut<'a, T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T> ExactSizeIterator for IterMut<'a, T> {}
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T> FusedIterator for IterMut<'a, T> {}
+
 impl<'a, T> IterMut<'a, T> {
     /// Inserts the given element just after the element most recently returned by `.next()`.
     /// The inserted element does not appear in the iteration.
@@ -908,6 +914,9 @@ impl<T> DoubleEndedIterator for IntoIter<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> ExactSizeIterator for IntoIter<T> {}
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<T> FusedIterator for IntoIter<T> {}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> FromIterator<T> for LinkedList<T> {
     fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {

src/libcollections/str.rs

@@ -23,6 +23,7 @@ use core::str as core_str;
 use core::str::pattern::Pattern;
 use core::str::pattern::{Searcher, ReverseSearcher, DoubleEndedSearcher};
 use core::mem;
+use core::iter::FusedIterator;
 use rustc_unicode::str::{UnicodeStr, Utf16Encoder};
 
 use vec_deque::VecDeque;
@@ -136,6 +137,9 @@ impl<'a> Iterator for EncodeUtf16<'a> {
     }
 }
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a> FusedIterator for EncodeUtf16<'a> {}
+
 // Return the initial codepoint accumulator for the first byte.
 // The first byte is special, only want bottom 5 bits for width 2, 4 bits
 // for width 3, and 3 bits for width 4

src/libcollections/string.rs

@@ -57,7 +57,7 @@
 
 use core::fmt;
 use core::hash;
-use core::iter::FromIterator;
+use core::iter::{FromIterator, FusedIterator};
 use core::mem;
 use core::ops::{self, Add, AddAssign, Index, IndexMut};
 use core::ptr;
@@ -1995,3 +1995,6 @@ impl<'a> DoubleEndedIterator for Drain<'a> {
         self.iter.next_back()
     }
 }
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a> FusedIterator for Drain<'a> {}

src/libcollections/vec.rs

@@ -68,7 +68,7 @@ use core::cmp::Ordering;
 use core::fmt;
 use core::hash::{self, Hash};
 use core::intrinsics::{arith_offset, assume};
-use core::iter::FromIterator;
+use core::iter::{FromIterator, FusedIterator};
 use core::mem;
 use core::ops::{Index, IndexMut};
 use core::ops;
@@ -1845,6 +1845,9 @@ impl<T> DoubleEndedIterator for IntoIter<T> {
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<T> ExactSizeIterator for IntoIter<T> {}
 
+#[unstable(feature = "fused", issue = "35602")]
+impl<T> FusedIterator for IntoIter<T> {}
+
 #[stable(feature = "vec_into_iter_clone", since = "1.8.0")]
 impl<T: Clone> Clone for IntoIter<T> {
     fn clone(&self) -> IntoIter<T> {
@@ -1932,3 +1935,6 @@ impl<'a, T> Drop for Drain<'a, T> {
 
 #[stable(feature = "rust1", since = "1.0.0")]
 impl<'a, T> ExactSizeIterator for Drain<'a, T> {}
+
+#[unstable(feature = "fused", issue = "35602")]
+impl<'a, T> FusedIterator for Drain<'a, T> {}