Support generic associated consts

src/test/compile-fail/associated-const-array-len.rs

@@ -0,0 +1,21 @@
+// 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.
+
+#![feature(associated_consts)]
+
+trait Foo {
+    const ID: usize;
+}
+
+const X: [i32; <i32 as Foo>::ID] = [0, 1, 2]; //~ ERROR E0250
+
+fn main() {
+    assert_eq!(1, X);
+}