Prefer string concat to format
@@ -191,7 +191,7 @@ fn try_save(path: &Path, text: &Rope, encoding: CharacterEncoding) -> io::Result
let tmp_extension = path
.extension()
.and_then(|extension| extension.to_str())
- .map_or_else(|| "swp".to_string(), |extension| format!("{}.swp", extension));
+ .map_or_else(|| "swp".to_string(), |extension| extension.to_string() + ".swp");
let tmp_path = &path.with_extension(tmp_extension);
let mut f = File::create(tmp_path)?;
