Forbid coercing unsafe functions to closures

Closes #9582

src/librustc/middle/typeck/infer/coercion.rs

@@ -410,7 +410,7 @@ impl Coerce {
         debug!("coerce_from_bare_fn(a={}, b={})",
                a.inf_str(self.get_ref().infcx), b.inf_str(self.get_ref().infcx));
 
-        if !fn_ty_a.abis.is_rust() {
+        if !fn_ty_a.abis.is_rust() || fn_ty_a.purity != ast::ImpureFn {
             return self.subtype(a, b);
         }
 

src/libstd/path/windows.rs

@@ -392,13 +392,13 @@ impl GenericPath for Path {
     #[inline]
     fn filestem_str<'a>(&'a self) -> Option<&'a str> {
         // filestem() returns a byte vector that's guaranteed valid UTF-8
-        self.filestem().map(cast::transmute)
+        self.filestem().map(|t| unsafe { cast::transmute(t) })
     }
 
     #[inline]
     fn extension_str<'a>(&'a self) -> Option<&'a str> {
         // extension() returns a byte vector that's guaranteed valid UTF-8
-        self.extension().map(cast::transmute)
+        self.extension().map(|t| unsafe { cast::transmute(t) })
     }
 
     fn dir_path(&self) -> Path {

src/test/compile-fail/coerce-unsafe-to-closure.rs

@@ -0,0 +1,14 @@
+// Copyright 2014 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.
+
+fn main() {
+    let x: Option<&[u8]> = Some("foo").map(std::cast::transmute);
+    //~^ ERROR: mismatched types
+}