Rework control flow in update_config

Author: kamalmarhubi

src/bin/rustfmt.rs

@@ -114,14 +114,13 @@ fn update_config(config: &mut Config, matches: &Matches) -> Result<(), String> {
     config.verbose = matches.opt_present("verbose");
     config.skip_children = matches.opt_present("skip-children");
 
-    if let Some(write_mode) = matches.opt_str("write-mode") {
-        match WriteMode::from_str(&write_mode) {
-            Ok(write_mode) => config.write_mode = write_mode,
-            Err(_) => return Err(format!("Invalid write-mode: {}", write_mode)),
-        }
+    let write_mode = matches.opt_str("write-mode");
+    match matches.opt_str("write-mode").map(|wm| WriteMode::from_str(&wm)) {
+        None => Ok(()),
+        Some(Ok(write_mode)) => { config.write_mode = write_mode; Ok(()) },
+        Some(Err(_)) => Err(format!("Invalid write-mode: {}",
+                                    write_mode.expect("cannot happen"))),
     }
-
-    Ok(())
 }
 
 fn execute() -> i32 {