NaN patterns: indicate that is_NaN is a method

src/librustc/middle/check_match.rs

@@ -119,7 +119,7 @@ pub fn check_arms(cx: &MatchCheckCtxt, arms: &[arm]) {
             for walk_pat(*pat) |p| {
                 if pat_matches_nan(p) {
                     cx.tcx.sess.span_warn(p.span, "unmatchable NaN in pattern, \
-                                                   use is_NaN() in a guard instead");
+                                                   use the is_NaN method in a guard instead");
                 }
             }
 

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

@@ -8,12 +8,12 @@ fn main() {
         NaN => {},
         _ => {},
     };
-    //~^^^ WARNING unmatchable NaN in pattern, use is_NaN() in a guard instead
+    //~^^^ WARNING unmatchable NaN in pattern, use the is_NaN method in a guard instead
     match [x, 1.0] {
         [NaN, _] => {},
         _ => {},
     };
-    //~^^^ WARNING unmatchable NaN in pattern, use is_NaN() in a guard instead
+    //~^^^ WARNING unmatchable NaN in pattern, use the is_NaN method in a guard instead
 }
 
 // At least one error is needed so that compilation fails