// Copyright 2014-2015 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.

pub fn cmd(name: &str) -> String {
    if cfg!(windows) {
        format!("{}.bat", name)
    } else {
        name.to_string()
    }
}

// Copyright 2014-2015 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.

#[cfg(not(windows))]
pub fn cmd(name: &str) -> String {
    name.to_string()
}

#[cfg(windows)]
pub fn cmd(name: &str) -> String {
    [name, ".bat"].concat()
}

--- 
+++ 
@@ -8,12 +8,10 @@
 // option. This file may not be copied, modified, or distributed
 // except according to those terms.
 
-#[cfg(not(windows))]
 pub fn cmd(name: &str) -> String {
-    name.to_string()
+    if cfg!(windows) {
+        format!("{}.bat", name)
+    } else {
+        name.to_string()
+    }
 }
-
-#[cfg(windows)]
-pub fn cmd(name: &str) -> String {
-    [name, ".bat"].concat()
-}
Use cfg!() to get type checking everywhere.
