From 265dce66b6b1181f4b955032b742c702c753f6c8 Mon Sep 17 00:00:00 2001
From: Scott McMurray <scottmcm@users.noreply.github.com>
Date: Tue, 30 May 2017 09:15:25 -0700
Subject: [PATCH] RangeFrom should have an infinite size_hint

This makes the size_hint from things like `take` more precise.
---
 src/libcore/iter/iterator.rs | 3 ++-
 src/libcore/iter/range.rs    | 5 +++++
 src/libcore/tests/iter.rs    | 1 +
 3 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/src/libcore/iter/iterator.rs b/src/libcore/iter/iterator.rs
index 77cbdb98c8304..85149a0f57078 100644
--- a/src/libcore/iter/iterator.rs
+++ b/src/libcore/iter/iterator.rs
@@ -130,9 +130,10 @@ pub trait Iterator {
     ///
     /// ```
     /// // an infinite iterator has no upper bound
+    /// // and the maximum possible lower bound
     /// let iter = 0..;
     ///
-    /// assert_eq!((0, None), iter.size_hint());
+    /// assert_eq!((usize::max_value(), None), iter.size_hint());
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
diff --git a/src/libcore/iter/range.rs b/src/libcore/iter/range.rs
index e02823fd81280..c0313333ea9ee 100644
--- a/src/libcore/iter/range.rs
+++ b/src/libcore/iter/range.rs
@@ -543,6 +543,11 @@ impl<A: Step> Iterator for ops::RangeFrom<A> where
         mem::swap(&mut n, &mut self.start);
         Some(n)
     }
+
+    #[inline]
+    fn size_hint(&self) -> (usize, Option<usize>) {
+        (usize::MAX, None)
+    }
 }
 
 #[unstable(feature = "fused", issue = "35602")]
diff --git a/src/libcore/tests/iter.rs b/src/libcore/tests/iter.rs
index 4030eaf2b2333..44d5936c63edd 100644
--- a/src/libcore/tests/iter.rs
+++ b/src/libcore/tests/iter.rs
@@ -764,6 +764,7 @@ fn test_iterator_size_hint() {
     let v2 = &[10, 11, 12];
     let vi = v.iter();
 
+    assert_eq!((0..).size_hint(), (usize::MAX, None));
     assert_eq!(c.size_hint(), (usize::MAX, None));
     assert_eq!(vi.clone().size_hint(), (10, Some(10)));