Use is_empty in range iteration exhaustion tests

src/libcore/ops/range.rs

@@ -262,6 +262,13 @@ impl<Idx: PartialOrd<Idx>> RangeTo<Idx> {
 /// The `RangeInclusive` `start..=end` contains all values with `x >= start`
 /// and `x <= end`.
 ///
+/// This iterator is [fused], but the specific values of `start` and `end` after
+/// iteration has finished are **unspecified** other than that [`.is_empty()`]
+/// will return `true` once no more values will be produced.
+///
+/// [fused]: ../iter/trait.FusedIterator.html
+/// [`.is_empty()`]: #method.is_empty
+///
 /// # Examples
 ///
 /// ```
@@ -329,6 +336,17 @@ impl<Idx: PartialOrd<Idx>> RangeInclusive<Idx> {
     /// assert!(!(3..=3).is_empty());
     /// assert!( (3..=2).is_empty());
     /// ```
+    ///
+    /// This method returns `true` after iteration has finished:
+    ///
+    /// ```
+    /// #![feature(range_is_empty,inclusive_range_syntax)]
+    ///
+    /// let mut r = 3..=5;
+    /// for _ in r.by_ref() {}
+    /// // Precise field values are unspecified here
+    /// assert!(r.is_empty());
+    /// ```
     #[unstable(feature = "range_is_empty", reason = "recently added", issue = "123456789")]
     pub fn is_empty(&self) -> bool {
         !(self.start <= self.end)

src/libcore/tests/iter.rs

@@ -1322,42 +1322,84 @@ fn test_range() {
                (isize::MAX as usize + 2, Some(isize::MAX as usize + 2)));
 }
 
+#[test]
+fn test_range_exhaustion() {
+    let mut r = 10..10;
+    assert!(r.is_empty());
+    assert_eq!(r.next(), None);
+    assert_eq!(r.next_back(), None);
+    assert_eq!(r, 10..10);
+
+    let mut r = 10..12;
+    assert_eq!(r.next(), Some(10));
+    assert_eq!(r.next(), Some(11));
+    assert!(r.is_empty());
+    assert_eq!(r, 12..12);
+    assert_eq!(r.next(), None);
+
+    let mut r = 10..12;
+    assert_eq!(r.next_back(), Some(11));
+    assert_eq!(r.next_back(), Some(10));
+    assert!(r.is_empty());
+    assert_eq!(r, 10..10);
+    assert_eq!(r.next_back(), None);
+
+    let mut r = 100..10;
+    assert!(r.is_empty());
+    assert_eq!(r.next(), None);
+    assert_eq!(r.next_back(), None);
+    assert_eq!(r, 100..10);
+}
+
 #[test]
 fn test_range_inclusive_exhaustion() {
     let mut r = 10..=10;
     assert_eq!(r.next(), Some(10));
-    assert_eq!(r, 1..=0);
+    assert!(r.is_empty());
+    assert_eq!(r.next(), None);
+    assert_eq!(r.next(), None);
 
     let mut r = 10..=10;
     assert_eq!(r.next_back(), Some(10));
-    assert_eq!(r, 1..=0);
+    assert!(r.is_empty());
+    assert_eq!(r.next_back(), None);
 
     let mut r = 10..=12;
     assert_eq!(r.next(), Some(10));
     assert_eq!(r.next(), Some(11));
     assert_eq!(r.next(), Some(12));
-    assert_eq!(r, 1..=0);
+    assert!(r.is_empty());
+    assert_eq!(r.next(), None);
 
     let mut r = 10..=12;
     assert_eq!(r.next_back(), Some(12));
     assert_eq!(r.next_back(), Some(11));
     assert_eq!(r.next_back(), Some(10));
-    assert_eq!(r, 1..=0);
+    assert!(r.is_empty());
+    assert_eq!(r.next_back(), None);
 
     let mut r = 10..=12;
     assert_eq!(r.nth(2), Some(12));
-    assert_eq!(r, 1..=0);
+    assert!(r.is_empty());
+    assert_eq!(r.next(), None);
 
     let mut r = 10..=12;
     assert_eq!(r.nth(5), None);
-    assert_eq!(r, 1..=0);
+    assert!(r.is_empty());
+    assert_eq!(r.next(), None);
 
     let mut r = 100..=10;
     assert_eq!(r.next(), None);
+    assert!(r.is_empty());
+    assert_eq!(r.next(), None);
+    assert_eq!(r.next(), None);
     assert_eq!(r, 100..=10);
 
     let mut r = 100..=10;
     assert_eq!(r.next_back(), None);
+    assert!(r.is_empty());
+    assert_eq!(r.next_back(), None);
+    assert_eq!(r.next_back(), None);
     assert_eq!(r, 100..=10);
 }
 
@@ -1427,10 +1469,11 @@ fn test_range_inclusive_nth() {
     assert_eq!(r, 13..=20);
     assert_eq!(r.nth(2), Some(15));
     assert_eq!(r, 16..=20);
+    assert_eq!(r.is_empty(), false);
     assert_eq!(ExactSizeIterator::is_empty(&r), false);
     assert_eq!(r.nth(10), None);
+    assert_eq!(r.is_empty(), true);
     assert_eq!(ExactSizeIterator::is_empty(&r), true);
-    assert_eq!(r, 1..=0);  // We may not want to document/promise this detail
 }
 
 #[test]
@@ -1514,11 +1557,11 @@ fn test_range_inclusive_folds() {
 
     let mut it = 10..=20;
     assert_eq!(it.try_fold(0, |a,b| Some(a+b)), Some(165));
-    assert_eq!(it, 1..=0);
+    assert!(it.is_empty());
 
     let mut it = 10..=20;
     assert_eq!(it.try_rfold(0, |a,b| Some(a+b)), Some(165));
-    assert_eq!(it, 1..=0);
+    assert!(it.is_empty());
 }
 
 #[test]