Update compiler error 0027 to use new error format.

Author: silenuss

src/librustc_typeck/check/_match.rs

@@ -700,9 +700,11 @@ impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
             for field in variant.fields
                 .iter()
                 .filter(|field| !used_fields.contains_key(&field.name)) {
-                span_err!(tcx.sess, span, E0027,
-                    "pattern does not mention field `{}`",
-                    field.name);
+                struct_span_err!(tcx.sess, span, E0027,
+                                "pattern does not mention field `{}`",
+                                field.name)
+                                .span_label(span, &format!("missing field `{}`", field.name))
+                                .emit();
             }
         }
     }

src/test/compile-fail/E0027.rs

@@ -17,6 +17,8 @@ fn main() {
     let d = Dog { name: "Rusty".to_string(), age: 8 };
 
     match d {
-        Dog { age: x } => {} //~ ERROR E0027
+        Dog { age: x } => {}
+        //~^ ERROR pattern does not mention field `name`
+        //~| NOTE missing field `name`
     }
 }