add back test for issue rust-lang#6804

Author: arielb1

src/test/compile-fail/issue-6804.rs

@@ -0,0 +1,34 @@
+// 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.
+
+#![feature(rustc_attrs)]
+#![feature(slice_patterns)]
+#![allow(dead_code)]
+#![deny(illegal_floating_point_constant_pattern)]
+
+// Matching against NaN should result in a warning
+
+use std::f64::NAN;
+
+#[rustc_error]
+fn main() {
+    let x = NAN;
+    match x {
+        NAN => {}, //~ ERROR floating point constants cannot be used
+                   //~| WARNING hard error
+        _ => {},
+    };
+
+    match [x, 1.0] {
+        [NAN, _] => {}, //~ ERROR floating point constants cannot be used
+                        //~| WARNING hard error
+        _ => {},
+    };
+}