Auto merge of #21806 - edwardw:new-range-impl, r=alexcrichton

The new `::ops::Range` has separated implementations for each of the
numeric types, while the old `::iter::Range` has one for type `Int`.
However, we do not take output bindings into account when selecting
traits. So it confuses `typeck` and makes the new range does not work as
good as the old one when it comes to type inference.

This patch implements `Iterator` for the new range for one type `Int`.
This limitation could be lifted, however, if we ever reconsider the
output types' role in type inference.

Closes #21595
Closes #21649
Closes #21672

src/test/run-pass/range-type-infer.rs

@@ -0,0 +1,28 @@
+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// Make sure the type inference for the new range expression work as
+// good as the old one. Check out issue #21672, #21595 and #21649 for
+// more details.
+
+fn main() {
+    let xs = (0..8).map(|i| i == 1u64).collect::<Vec<_>>();
+    assert_eq!(xs[1], true);
+    let xs = (0..8).map(|i| 1u64 == i).collect::<Vec<_>>();
+    assert_eq!(xs[1], true);
+    let xs: Vec<u8> = (0..10).collect();
+    assert_eq!(xs.len(), 10);
+
+    for x in 0..10 { x % 2; }
+    for x in 0..100 { x as f32; }
+
+    let array = [true, false];
+    for i in 0..1 { array[i]; }
+}