fix u32 steps_between for 16-bit systems

src/libcore/iter/range.rs

@@ -165,8 +165,16 @@ macro_rules! step_impl_no_between {
     )*)
 }
 
-step_impl_unsigned!(usize u8 u16 u32);
-step_impl_signed!([isize: usize] [i8: u8] [i16: u16] [i32: u32]);
+step_impl_unsigned!(usize u8 u16);
+#[cfg(not(target_pointer_witdth = "16"))]
+step_impl_unsigned!(u32);
+#[cfg(target_pointer_witdth = "16")]
+step_impl_no_between!(u32);
+step_impl_signed!([isize: usize] [i8: u8] [i16: u16]);
+#[cfg(not(target_pointer_witdth = "16"))]
+step_impl_signed!([i32: u32]);
+#[cfg(target_pointer_witdth = "16")]
+step_impl_no_between!(i32);
 #[cfg(target_pointer_width = "64")]
 step_impl_unsigned!(u64);
 #[cfg(target_pointer_width = "64")]

src/test/run-pass/issue-48006.rs

@@ -0,0 +1,23 @@
+// Copyright 2018 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.
+
+#![feature(step_trait)]
+
+use std::iter::Step;
+
+#[cfg(target_pointer_width = "16")]
+fn main() {
+    assert!(Step::steps_between(&0u32, &::std::u32::MAX).is_none());
+}
+
+#[cfg(any(target_pointer_width = "32", target_pointer_width = "64"))]
+fn main() {
+    assert!(Step::steps_between(&0u32, &::std::u32::MAX).is_some());
+}