Fix rustfmt according to review

Author: Nadrieril

Diff for: src/tools/rustfmt/src/patterns.rs

@@ -339,9 +339,9 @@ impl Rewrite for Pat {
                         .max_width_error(shape.width, self.span)?,
                 )
                 .map(|inner_pat| format!("({})", inner_pat)),
-            PatKind::Err(_) => Err(RewriteError::Unknown),
+            PatKind::Guard(..) => Ok(context.snippet(self.span).to_string()),
             PatKind::Deref(_) => Err(RewriteError::Unknown),
-            PatKind::Guard(..) => Err(RewriteError::Unknown),
+            PatKind::Err(_) => Err(RewriteError::Unknown),
         }
     }
 }

Diff for: src/tools/rustfmt/tests/target/guard_patterns.rs

@@ -0,0 +1,12 @@
+#![feature(guard_patterns)]
+
+fn main() {
+    match user.subscription_plan() {
+        (Plan::Regular if user.credit() >= 100) | (Plan::Premium if user.credit() >= 80) => {
+            // Complete the transaction.
+        }
+        _ => {
+            // The user doesn't have enough credit, return an error message.
+        }
+    }
+}