fix silent overflows on Step impls

src/libcore/iter/range.rs

@@ -95,11 +95,13 @@ macro_rules! step_impl_unsigned {
             }
 
             #[inline]
+            #[rustc_inherit_overflow_checks]
             fn add_one(&self) -> Self {
                 *self + 1
             }
 
             #[inline]
+            #[rustc_inherit_overflow_checks]
             fn sub_one(&self) -> Self {
                 *self - 1
             }
@@ -166,11 +168,13 @@ macro_rules! step_impl_signed {
             }
 
             #[inline]
+            #[rustc_inherit_overflow_checks]
             fn add_one(&self) -> Self {
                 *self + 1
             }
 
             #[inline]
+            #[rustc_inherit_overflow_checks]
             fn sub_one(&self) -> Self {
                 *self - 1
             }
@@ -215,11 +219,13 @@ macro_rules! step_impl_no_between {
             }
 
             #[inline]
+            #[rustc_inherit_overflow_checks]
             fn add_one(&self) -> Self {
                 *self + 1
             }
 
             #[inline]
+            #[rustc_inherit_overflow_checks]
             fn sub_one(&self) -> Self {
                 *self - 1
             }

src/test/run-fail/iter-step-overflow-debug.rs

@@ -0,0 +1,27 @@
+// Copyright 2016 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.
+
+// compile-flags: -C debug_assertions=yes
+
+use std::panic;
+
+fn main() {
+    let r = panic::catch_unwind(|| {
+        let mut it = u8::MAX..;
+        it.next();
+    });
+    assert!(r.is_err());
+
+    let r = panic::catch_unwind(|| {
+        let mut it = i8::MAX..;
+        it.next();
+    });
+    assert!(r.is_err());
+}

src/test/run-fail/iter-step-overflow-ndebug.rs

@@ -0,0 +1,19 @@
+// Copyright 2016 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.
+
+// compile-flags: -C debug_assertions=no
+
+fn main() {
+    let mut it = u8::MAX..;
+    assert_eq!(it.next(), u8::MIN);
+
+    let mut it = i8::MAX..;
+    assert_eq!(it.next(), i8::MIN);
+}