Rollup merge of rust-lang#21404 - japaric:hash, r=alexcrichton

closes rust-lang#21402
cc rust-lang#15294

r? @alexcrichton or @aturon 
cc @ExpHP (btw, this only covers arrays with arity up to 32)

src/libcore/array.rs

@@ -17,6 +17,7 @@
 use clone::Clone;
 use cmp::{PartialEq, Eq, PartialOrd, Ord, Ordering};
 use fmt;
+use hash::{Hash, Hasher, self};
 use marker::Copy;
 use ops::{Deref, FullRange};
 use option::Option;
@@ -32,6 +33,12 @@ macro_rules! array_impls {
                 }
             }
 
+            impl<S: hash::Writer + Hasher, T: Hash<S>> Hash<S> for [T; $N] {
+                fn hash(&self, state: &mut S) {
+                    Hash::hash(&self[], state)
+                }
+            }
+
             #[unstable = "waiting for Show to stabilize"]
             impl<T:fmt::Show> fmt::Show for [T; $N] {
                 fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {

src/test/run-pass/issue-21402.rs

@@ -0,0 +1,18 @@
+// 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.
+
+#[derive(Hash)]
+struct Foo {
+    a: Vec<bool>,
+    b: (bool, bool),
+    c: [bool; 2],
+}
+
+fn main() {}