Rollup merge of #42315 - scottmcm:rangefrom-sizehint, r=alexcrichton

RangeFrom should have an infinite size_hint

Before,
```rust
(0..).take(4).size_hint() == (0, Some(4))
```

With this change,
```rust
(0..).take(4).size_hint() == (4, Some(4))
```

1 files changed, 2 insertions, 1 deletions

diff --git a/src/libcore/iter/iterator.rs b/src/libcore/iter/iterator.rs
index 77cbdb98c83..85149a0f570 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")]